Status of KEKB B-Factory

K. Akai, N. Akasaka, A. Enomoto, J. Flanagan, H. Fukuma, Y. Funakoshi, K. Furukawa, S. Hiramatsu, K. Hosoyama, T. Ieiri, N. Iida, T. Kamitani, S. Kato, M. Kikuchi, E. Kikutani, H. Koiso, S.-I. Kurokawa, M. Masuzawa, T. Matsumoto, S. Michizono, T. Mimashi, T. Nakamura, Y. Ogawa, K. Ohmi, Y. Ohnishi, S. Ohsawa, N. Ohuchi, K. Oide, E. A. Perevedentsev*, K. Satoh, M. Suetake, Y. Suetsugu, T. Suwada, M. Tawada, M. Tejima, M. Tobiyama, N. Yamamoto, M. Yoshida, S. Yoshimoto, F. Zimmermann**
KEK, BINP(*), CERN(**)

The status of the KEKB B-Factory, after EPAC, will be reported. The topics are (1) luminosity performance, (2) LER blowup and the effect of solenoid, and (3) roadmap for the design luminosity.

HIGH LUMINOSITY POLARIZED PROTON COLLISIONS AT RHIC

Thomas Roser
Brookhaven National Laboratory Collider-Accelerator Department

The Brookhaven Relativistic Heavy Ion Collider (RHIC) provides the unique opportunity to collide polarized proton beams at a center-of-mass energy of up to 500 GeV and luminosities of up to 2x10^32 cm^-2 s^-1. Such high luminosity and high energy polarized proton collisions will open up the possibility of studying spin effects in hard processes. However, the acceleration of polarized beams in circular accelerators is complicated by the numerous depolarizing spin resonances. Using a partial Siberian Snake and a rf dipole that ensure stable adiabatic spin motion during acceleration has made it possible to accelerate polarized protons to 25 GeV at the Brookhaven AGS. After successful operation of RHIC with gold beams polarized protons from the AGS have been successfully injected into RHIC and accelerated using a full Siberian Snakes built from four superconducting helical dipoles. A new high energy proton polarimeter was also successfully commissioned. Operation with two Snakes per RHIC ring is planned for next year.

RHIC commissioning with Au ions

Dejan Trbojevic
Collider Accelerator Department, Brookhaven National Laboratory

The Relativistic Heavy Ion Collider (RHIC) had been successfully put into operation and provided collisions of the fully stripped gold ions at a beam energy of 65 GeV/nucleon during summer 2000. All four experiments "STAR", "PHENIX", "PHOBOS", and "BRAHMS" collected more than 3 inverse micro barn of data. We present details of both the gold beam commissioning as well as from the collision run. We will show measurements of betatron and dispersion functions that are, after corrections, in excellent agreement with prediction. Diagnostic results from tune meter, wall current monitor, chromaticity and decoupling measurements, ionization beam profile monitor, Schottky monitors, etc. will also be shown. Operational experience for establishing gold ion beam stores with optimized luminosity will be discussed as well as plans for future runs and possible future machine upgrades.

e+e- FACTORIES - THE NEXT GENERATION

David Rice
CORNELL UNIVERSITY Ithaca, NY USA

Through most of the history of electron-positron colliding beam storage rings, realized performance has lagged significantly behind design performance figures. Design parameters were met or exceeded only after significant modifications of the machines. With the latest generation of electron positron factories we are beginning to see design parameters achieved in the original configuration of the machine. This change reflects the tremendous knowledge accumulated over years of studies and experience with these machines. The next generation of lepton factories will reach a luminosity beyond 10E35 /cm2/sec. The designs must take into account effects which are just at their thresholds in present machines. New techniques to reach high space charge density at the interaction point and large collision currents will play critical roles in these colliders. The experience over the past few years gives good confidence that, carefully planned, these machines will achieve design luminosity.

STATUS OF DAFNE

Miro Preger, for the DAFNE Commissioning Team
INFN-LNF, Frascati, Italy

DAFNE is a double ring electron-positron collider, designed to run with high luminosity at the energy of the Phi resonance (1.02 GeV c.m.). After storing the first beam in fall 1997, the collider was commissioned without solenoidal detectors until the end of 1998, reaching a single bunch luminosity of 1.6x10^30 cm^-2 s^-1 with 20 mA in each beam, corresponding to a beam-beam tune shift of 0.03. A longitudinal bunch-to-bunch feedback has been implemented, allowing the storage of more than 0.5 A in 30 bunches for both electrons and positrons. The KLOE detector, embedded into a superconducting solenoid with strong longitudinal integrated field (2.4 Tm to be compared to a magnetic rigidity of 1.7 Tm) compensated by two other solenoids of opposite field, was installed in winter 1999 and commissioning resumed with a careful correction of the coupling effects. After the installation of the detector, however, the single bunch peak luminosity does not exceed 5x10^29 cm^-2 s^-1, corresponding to tune shifts of the order of 0.015, with a typical luminosity lifetime of half an hour. Particular effort has been dedicated to the reduction of background in the experiment, which led to the possibility of injecting the beams in interaction without switching off data acquisition. The total stored current has reached more than 1 A in each beam, while a transverse feedback system has been realized to counteract vertical instabilities occurring during injection. The collider is now running in the multibunch mode forKLOE data taking with peak luminosity up to 1.5x10^31 cm^-2 s^1 and integrated luminosity larger than 0.5 pb^-1 per day. A discussion of the problems connected with single bunch luminosity and multibunch dynamics, together with the developments foreseen to improve the performance of the collider, is presented.

STATUS REPORT AND FUTURE PLANS FOR THE PEP-II B FACTORY

Alan S. Fisher
Stanford Linear Accelerator Center for the PEP-II Group

The PEP-II B Factory at SLAC has been in operation with the BABAR detector since the summer of 1999. The peak currents and luminosity have steadily increased through the end of the 2000 run on 31 October. By that time, 0.75 A of electrons (the design current) routinely collided with 1.4 A of positrons in 657 bunches, to give a peak luminosity of 2.5E33. We delivered an integrated luminosity of up to 160/pb per day and 900 per week; BABAR has logged a total of 23.5/fb. Three days of machine development at the end of the run raised the peak luminosity to 3.1E33, exceeding the design goal of 3.0. BABAR logged data for an hour starting with a peak of 3.0. Next, we achieved the design value for the positron current, 2.15 A, operating without collisions. The major limitation has been beam-size growth in the low-energy (positron) ring due to electron clouds and multipactoring. Since the arcs benefit from antechambers and a TiN coating with low secondary emission, our efforts have concentrated on adding solenoid windings to the straights. Each straight wound allowed higher LER current without blow-up and a consequent increase in luminosity. Measurements of the bunch-by-bunch luminosity have shown that the effect becomes significant by about the tenth bunch in a train, but clears after a short gap. Careful control of the fill pattern has thus been essential in raising luminosity. When the 2001 run begins in February, we will add a third LER RF station, to collide with more LER current and more bunches, and also reduce beta_y* from 12.5 to 10 mm, with the goal of reaching a luminosity of 5E33 by year's end. In 2003, we plan to add the fourth LER and sixth HER RF station to reach 1E34.

Higher-Order Multipole Analysis of Beam-Induced Electromagnetic Fields Using a Stripline-Type Beam Position Monitor

Tsuyoshi Suwada
Accelerator Laboratory High Energy Accelerator Research Organization (KEK) 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan

A measurement of multipole moments of an electromagnetic field generated by single-bunch electron beams with a pulse width of 10 ps was performed by using beam-position monitors (BPMs) at the KEKB injector linac. A theoretical multipole analysis agrees well with the experimental results within the measurement errors. The measurement enables one to measure the transverse spatial profile of charged beams; especially, the variations of the higher-order moments were well consistent with those measured by wire scanners. The result also shows that the electromagnetic response of the BPM can be well treated as an electrostatic potential problem in which image charges are induced by a line charge on a conducting round duct. This report describes in detail an experimental multipole analysis for single-bunch electron beams by using stripline-type beam-position monitors with four electromagnetic pickups.

RESISTIVE WALL AND BEAM BREAKUP MULTIBUNCH INSTABILITIES IN BEAM WITH LONG GAPS

H. Fukuma
High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba-shi, Ibaraki-ken 305-0801, Japan
D. Pestrikov
Budker Institute of Nuclear Physics, 630090 Novosibirsk, Russian Federation

In circular accelerators and storage rings weak, but long-range wake fields close the feedback coupling of multibunch oscillations in a beam which has a long bunch gap containing no bunches. Even if the leading perturbation of the coherent oscillations occurs due to a strong wake with the memory shorter than the gap, the effects of these weak, but long-range wakes eliminate a possibility of the beam breakup multibunch instabilities in circular machines because the oscillations are expressed by well defined eigenfunctions which are exponential functions of time. We discuss main features of resulting multibunch modes and their relation to conventional beam breakup instabilities.

TRANSVERSE MULTIBUNCH COHERENT MODES OF BEAM WITH A GAP

H. Fukuma
High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba-shi, Ibaraki-ken 305-0801, Japan
D. Pestrikov
Budker Institute of Nuclear Physics, 630090 Novosibirsk, Russian Federation

In the multibunch beam with a uniform filing pattern, coherent oscillations are described by the eigensolutions of multibunch modes that have constant amplitudes along the beam. A gap without bunches in the beam introduces an obstacle for the propagation of these coherent oscillations. If the memory of wakes is longer than the length of the gap, the interaction of bunches is still described solving the eigenvalue problem. However, due to this obstacle the energy of coherent motion is accumulated towards the end of the bunch train, thus the amplitudes of the multibunch eigensolutions are amplified along the train. Such an amplification of the amplitudes along the train can simulate beam breakup instabilities. Even if the oscillations are damped using a conventional bunch by bunch feedback system, this amplification of oscillations can limit the beam performance in high current operation of accelerators.

Effects of tune modulation on the long-term stability

Eun-San Kim and Moohyun Yoon
Pohang Accelerator Laboratory, POSTECH, San 31,
Hjoja Dong,
Pohang, Kyungbuk, Korea, 790-784

The combined effects of beam-beam interaction and a tune modulation are investigated in terms of the long-term stability in electron collider rings. The tune modulation by the power supply ripples is considered. The transverse tunes are sinusoidally modulated at different amplitudes and frequencies of the ripples. It is shown that choices of synchrotron tune affect the beam blowup through the beam-beam interaction. It is shown that the combined effects of beam-beam interaction and a tune modulation result in beam blowup in electron collider rings.

STUDY OF VERTICAL BEAM BLOW-UP IN KEKB LOW ENERGY RING

H. Fukuma, K. Akai, N. Akasaka, A. Enomoto, J. W. Flanagan, Y. Funakoshi, K. Furukawa, S. Hiramatsu, T. Ieiri, N. Iida, S. Kato, M. Kikuchi, E. Kikutani, H. Koiso, T. Mitsuhashi, M. Masuzawa, T. Matsumoto, T. Mimashi, T. Nakamura, Y. Ogawa, K. Ohmi, Y. Ohnishi, S. Ohsawa, N. Ohuchi, K. Oide, K. Satoh, M. Suetake, Y. Suetsugu, T. Suwada, M. Tawada, M. Tejima, M. Tobiyama, N. Yamamoto, M. Yoshida, S. Yoshimoto, F. Zimmermann*
High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba-shi, Ibaraki-ken 305-0801, Japan

*visiting from CERN, Switzerland

A blow-up of the vertical beam size in single beam and multibunch operation is observed in the KEKB positron ring (LER). At present the blow-up is the most serious problem limiting the luminosity of KEKB. The beam size starts to increase at a threshold beam current which depends almost on the charge density of the beam. Observations by fast gated camera show the beam size increases along the train of the bunches until it saturates. Based on speculation that the blow-up is caused by the electrons which are generated by the synchrotron radiation hitting the vacuum ducts, small permanent magnets (C-yokes) were attached on the vacuum ducts to sweep out the electrons. Although the C-yokes were effective for the long bunch spacings, they were not effective for the short bunch spacing in which the LER is operated in luminosity run. To remove the electrons in more efficient way, solenoids are being installed in this summer shut down. This paper describes the experimental study of the vertical beam blow-up emphasizing the effect of the solenoids.

Wake field and transverse mode coupling instability caused by electron cloud

K. Ohmi
KEK
F. Zimmermann
CERN
E. Perevedentsev
BINP

In positron and proton storage rings, electrons produced by photo-emission, ionization and secondary emission accumulate in the vacuum chamber for multi-bunch operation with close spacing. A positron or proton bunch passing through this `electron cloud' experiences a short-range wake field. This wake field can cause a transverse mode coupling instability, if the electron-cloud density exceeds a threshold value. We study the electron-cloud induced wake field using analytic and simulation approaches, evaluate theoretical expressions for the transverse mode coupling instability based on the linearized Vlasov equation, and examine the dependence of the instability threshold on chromaticity.

Lattice Diagnostics in the KEKB Colliding Rings

H. Koiso, N. Akasaka, H. Fukuma, Y. Funakoshi, Y. Ohnishi, K. Oide

The KEKB rings have been operated with low-beta optics of by*=0.7 cm. Systematic correction of beam-optical functions is important to realize stable operation at high luminosity. The beta function, dispersion, x-y coupling are measured at beam position monitors over the rings and are corrected effectively by using two kinds of tuning knobs: fine adjustment of power supplies of magnets and local orbit bumps at the sextupoles. As a result of the corrections, the vertical-to-horizontal emittance ration is reduced to 1% in both rings at low beam currents. In this paper, recent results and improvements on the optics corrections are discussed.

MEASUREMENTS OF BETATRON TUNE ALONG BUNCH TRAIN IN THE KEKB LOW ENERGY RING

Takao Ieiri, Hitoshi Fukuma, Takashi Kawamoto and Makoto Tobiyama
KEK, Accelerator Laboratory

A fast gate module has been developed in the KEKB, which can pick up
a signal of one bunch in multi-bunched beam. We have measured bunch-by-bunch betatron tunes along a bunch train using the gate module in the low-energy positron ring. The characteristics of the measurement system are described. We can estimate the electron density from the tune shift, since electrons produced by photo-emission and/or secondary emission and attracted by successive positron bunches would result in shifting a coherent betatron tune of positron bunches. The estimated electron density from the tune shift is compared with the simulation[1]. A relation between the tune shift and enlarged vertical beam size[2] is discussed. [1] K. Ohmi and F. Zimmermann, KEK preprint 2000-19 (2000). [2] H. Fukuma et.al., EPAC 2000, Vienna (2000).

Injection in the storage ring VEPP-2000

Boris I. Grishanov and Fedor V. Podgorny
The Budker Institute of Nuclear Physics 630090 Novosibirsk, Russian Federation

In the spring of 1999 the decision was taken on the modernization of the VEPP-2M complex to increase the luminosity and the maximum achievable energy of up to 2 GeV. This will to essentially improve the experiments on the collider. The new project was named VEPP-2000. Engineering aspects of injection at VEPP-2000 are considered in this report. The energy of injection is 900 MeV. The scheme of injection with a prekick of a stored beam is used. As the collider has got one ring, both the electron and the positron beams co-exist and simultaneously move in counter directions. The kickers operate in a traveling wave mode and affect the counter moving particles only. Every kicker has one asymmetrical 50-Ohm strip lines with a unipolar feed. The geometrical aperture of the vacuum chamber is 34 x 70 sq. mm. The plates of the kickers are located inside the bending magnets and are 1400 mm long. Such tiny sizes of the chamber cause additional difficulties with ensuring both the placement and the electric strength of the plates in the chamber. The present report describes the feed circuit of the kickers. The generators form pulses in the traveling wave mode with an amplitude of up to 60 kV, 80 ns pulse duration (FWHM) and 60 ns raise/fall time at a repetition rate of up to 1 Hz. The circuit is constructed on the basis of a step artificial line with a pulse hydrogen thyratron as the switchboard.

HIGH-INTENSITY, TWO-BUNCH ACCELERATION FOR DOUBLING POSITRON PRODUCTION AT THE KEKB LINAC

Yujiro Ogawa, Atsushi Enomoto, Kazuro Furukawa, Hitoshi Kobayashi, Toshihiro Matsumoto, Satoshi Ohasawa, Tsuyoshi Suwada
High Energy Accelerator Research Organization (KEK)

Rapid injection of positrons into the KEKB ring is one of the most critical issues affecting the accumulation of integrated luminosity. The KEKB linac has until now injected single-bunch positron beams with charge of about 0.4 nC into the KEKB ring, requiring several minutes of injection time. In order to make this positron injection time as short as possible, we have introduced a high-intensity, two-bunch acceleration scheme in the primary electron beam for positron production, which could eventually double the positron intensity and halve the injection time. The bunch separation has been determined to be 96.29 ns, taking account of the SLED pulse width at the linac as well as the common frequency (10.385 MHz) of both the linac (2856 MHz) and the ring (508.887 MHz). First beam test results are reported.

High-power test stand for the ARES input coupler

Fujio Naito, Hiroshi Sakai, Shin-ichi Yoshimoto and Hajime Mizuno
KEK

A small cylindrical cavity is being used for the high-power conditioning (800 kW (CW), 509 MHz) of the input coupler developed for the ARES cavity of KEKB factory. Two couplers are set facing their loops each other at the center of the cavity. The gap distance between the loops is about 2 mm. Since the coupling between loops is very large, an rf loss in the cavity could be suppressed to very low levels. Thus the cooling system and the rf tuning system for the cavity became very simple. The design considerations and the RF characteristics of this high-power test system will be presented.

On the UHF high-power input coupler with a cylindrical ceramic wall

Hiroshi Sakai, Shin-ichi Yoshimoto, Fujio Naito and Hajime Mizuno
KEK

The UHF input coupler developed for the old TRISTAN electron-positron collider at KEK was analyzed with RF simulation code HFSS. To increase the maximum RF power, the rectangular waveguide part of the coupler was redesigned with the iris like structure and this iris like structure that is set at the rectangular waveguide side helped to achieve the lower and more uniform field on the ceramic surface. The RF measurement result of this developed coupler will be reported. The high-power test results on the old and the newly developed couplers will be presented.

HIGH POWER INPUT COUPLER OF SUPERCONDUCTING CAVITY FOR KEKB

Y. Kijima , The graduate university for advanced studies S.Mitsunobu , T.Furuya
KEK, High energy accelerator reseach organization
T.Tanaka
Furukawa Electric Co.

The added four superconducting cavities ware installed in the KEKB HER ring in August 2000. The input coupler is the key component of the superconducting cavity for high current operation. We conditioned the input coupler for four cavities up to 300kW of input power, while applying a DC bias voltage of up to ±2kV on the inner conductor. This RF aging with bias voltage was found to be effective in suppressing multipacting. We will present the multipacting process and the beam operation of the input coupler for the superconducting cavities.

DETECTION OF PHOTOELECTRON CLOUD IN POSITRON RING AT KEKB

K. Kanazawa, T. Murakami, Y. Ohnishi, M. Tanaka, M. Tejima
KEK

We have developed photoelectron detector and observed photoelectron cloudin the positron ring at KEKB. The detector system comprises two electrodes, one is a collector with a readout electronics and the other is a suppressor can provide electric field, and mesh-shield connected to the ground in the vacuum chamber. Photoelectron effect causes beam instability or vertical beam-size blow up is very serious for the high beam-current positron ring. We measured the amount of photoelectron and the behavior of decay for various beam current and bunch-filling patterns.

Bunch length measurement and the beam signal observation through high power RF waveguide system

Toshihiro Mimashi and Hajime Mizuno
KEK Accelerator Department
Hong Bo
IHEP Accelerator Department

Bunch length is measured using the beam induced signal in the RF cavity of KEKB Low energy ring. The beam signal propagates to the klystron gallery through the waveguide and is extracted with the small antenna. Since the bare spectrum of the bunch is observed up to 30GHz, the spectrum between 5 GHz and 30GHz is taken and fitted to calculate the bunch length. The measured bunch length is consistent with the design value and other bunch length measurement. The synchrotron oscillation and the vertical betatron oscillation side-band peaks are also observed by this system.

HIGH CURRENT AND HIGH POWER APPLICATION OF SUPERCONDUCTING CAVITIES FOR KEKB

Shinji Mitsunobu, Kazunori Akai, Eiji Ezura, Takaaki Furuya, kenji Hosoyama
KEK
Yuuko Kijima
Mitubishi Electric Co.
Richard Noer
Carleton College
Tsuyoshi Tajima
LosAramos National Lab.

KEKB is an asymmetric electron-positron collider at 8x3.5 GeV, which aims to provide electron-positron collision at a center of mass energy of 10.58 GeV. For 8 GeV high energy ring, four superconducting cavities have been used to accelerate high current of more than 500 mA. At the summer shutdown of 2000, fore more superconducting cavities have been installed to increase current up to 1.1 A. The cavity is single cell and has large diameter beam pipe to damp beam induced higher order mode power. The operation results of large application of superconducting cavity for high power and high current will be shown.

PROBLEMS AND IMPROVEMENTS OF THE MOVABLE MASK SYSTEM FOR KEKB

Yusuke Suetsugu, Nobumasa Akasaka, Tatsuya Kageyama, Yasunao Takeuchi, Kotaro Sato and Ken-ichi Kanazawa
KEK, Accelerator Lab.

The movable mask is a device that cuts of spent electrons/positrons near the beam orbit and reduces background of the detector. For the KEKB (KEK B-factory), sixteen movable masks had been installed for each ring. The originally designed masks, however, had severe troubles of heating, arcing and vacuum leaks. Several kinds of new masks had been designed partially employing RF technologies in dealing with HOM and were installed to the ring step by step. The latest masks are working almost as expected now. Here the problems of movable mask in each stage and countermeasures to them are reported. The structure of the latest movable masks and their status are also presented.

RF conditioning and operation of the co-axial input coupler for KEK-B ARES cavities

H.Mizuno, H.Sakai, M.Yoshimoto and F.Naito
KEK

The UHF high power coaxial ceramic window was developed for the KEK-B accelerating cavity system “ARES”. Total 26 couplers are under operation in the KEK-B electron and positron storage rings. RF driving power reached up to 300Kw on each coupler. Considering the over coupled condition without beam (Beta=3.0), the high power test must be carried up to 800kW . All couplers arrived to KEK, were tested up to 800kW at the test station. After the RF conditioning process up to 600kW at the test station, couplers were set in B-factory HER and LER. Last 1-year operation of KEK B-ring, couplers were successfully operated at the peak RF power of 300kW each. Some detail of the coupler test station that applies the low loss cavity with two couplers is also reported.

The klystron output impedence survey by irisis set in the waveguide system

H.Mizuno, S.Tokumoto, S.Matsumoto, Y.Ching, and K.Ohya
KEK

The load impedence of the output cavity of the X-band PPM klystron was adjusted by changing the position of each iris that were located at the downstream of the output ceramic windows. The load impedence of the output cavity changed with the factor factor 4. This load impedence change was measured as the small signal output power change, while the input power was kept constant. Under the small signal condition, the RF current at the output cavity was kept constant, and the output power was considered proportional to the output load impedence. The saturated output power measurements with various output load impedence demonstrated that the present cavity had the lower impedence than the best matching. Also the measured power difference between two output waveguides were explained as the load impedence difference between two ports due to the existance of reflection on each waveguide. Some details of this measurement are reported.

Beam Size Feedback System at KEKB

N.Iida, Y.Funakoshi, H.Koiso, M.Masuzawa and K.Oide
KEK

KEKB B-Factory is one of the second generation electron and positron colliders. The energies of the two beams are 3.5 GeV(positron) and 8 GeV(electron). In the usual beam operation, the LER (Low Energy Ring) beam is weaker than the HER (High Energy Ring) beam. We found that the LER vertical beam size can be shrinked by intentionally making the HER beam size bigger and then luminosity got higher when the LER beam is blown up due to the beam-beam effect. By making use of this mechanism, we have constructed a feedback system which keeps the beam size ratio of the two beams at some optimum values where the luminosity is maximum. We found that the feedback is a very useful tool for increasing the luminosity.

TWO-BUNCH BEAM GENERATION FOR KEKB

S. Ohsawa, M. Ikeda, A. Shirakawa, and K. Furukawa
High Energy Accelerator Research Organization (KEK) Tsukuba, Ibaraki, 305-0801 Japan

Two-bunch beams have been required to reduce injection times into KEKB rings. Especially for the LER it is being inevitable to increase positron intensity as the stored beam increases. Two-bunch beam acceleration is one of the methods to meet the requirement. In order to accelerate and accumulate the beams successfully, it is at least necessary to satisfy the following conditions: 1) each bunch length should be as short as the present single bunch, that is less than 10 ps, and 2) their time interval should be 97.29 ns that is a period of the common operation frequency between the linac and KEKB rings. Wake field effects are strong for high intensity beams. In normal acceleration sections beam energy of each bunch is thought to be controllable by means of changing acceleration timing with respect to RF pulses. In the bunching section, however, this technique is not useful. To obtain independent operation freedom we developed a system that produces a two-pulse b! eam from an electron gun each of which intensity and timing are independently changeable. Beam test results are presented as well as the system configuration and performance.

OPERATION SURVEILLANCE NETWORK IN THE KEKB LINAC PRE-INJECTOR

M. Ikeda, A. Shirakawa, K. Furukawa, and S. Ohsawa
High Energy Accelerator Research Organization (KEK) Tsukuba, Ibaraki, 305-0801 Japan

Fundamental characteristics of electron beams are determined in the pre-injector. Therefore high stability is required for each devise that comprises of the pre-injector, especially in high intensity beam acceleration. An operation surveillance network has been constructed and under operation. It is constantly monitoring many kinds of quantities concerning to beams such as beam timings, intensities and jitters, RF phases, high/low voltages, and room and water　temperatures. With other monitors such as RF monitors and BPM’s, it became easy to find changes. This network is useful to maintain stable operation. The present status will be given.

BEAM-BEAM EFFECT AT THE KEKB

Yoshihiro Funakoshi, John Flanagan, Haruyo Koiso, Mika Masuzawa, Kazushi Ohmi, Yukiyoshi Ohnishi, Katsunobu Oide and Masafumi Tawada
High Energy Accelerator Research Organization (KEK), Accelerator Laboratory

The KEKB is an energy asymmetric e+ - e- double-ring collider. Phenomena related to the beam-beam interaction are much more complicated and richer than conventional single ring colliders. Beam-beam tunings, which include detections and corrections of machine imperfections and choices of machine parameters such as beam emittances, have played an important role to raise the luminosity. This report summarizes experiences on beam-beam effects at the KEKB.

MULTI-TIER ACCELERATOR CONTROL SYSTEM AT KEK 8-GEV e-/e+ LINAC

Kazuro Furukawa and Norihiko Kamikubota
High Energy Accelerator Research Organization (KEK)

KEK 8-GeV linac injects electron and positron beams into the storage rings at B-factory (KEKB), Photon Factory (PF) and PF-AR. Because of frequent switching between these beam modes, a reliable beam operation of the linac is crucial. For this end a multi-tier control system has been developed and used. The lower-layer servers abstract hardware characteristics and the upper-layer server represents the property of accelerator equipment and the beam to the operation software. It also provides the interface to the downstream storage rings, which are operated by different control systems. The network and computer systems employ high-availability technologies in order to increase the reliability. Using these control services many pieces of operation software have been developed. They all provide essential functions to maintain the stable operation of the linac.

STATUS REPORT OF THE PEP-II Lower pressure HER vacuum chamber

S. DeBarger, S. Metcalfe, J. Seeman, M. Sullivan, U. Wienands, D. Wright
Stanford Linear Accelerator Center (SLAC), CA 94025 Accelerator Group

This new vacuum chamber is being installed from 12 to 21 meters upstream of the BaBar detector in the PEP-II High Energy Ring (HER) to reduce lost particle backgrounds. The backgrounds from HER now dominate the backgrounds in the BaBar detector and the present vacuum pressure is one nanoTorr. The new chamber will increase the pumping significantly by adding 18x 2000 l/s titanium sublimation pumps in addition to 5x 400 l/s Ion pumps, and is expected to reduce the pressure by about a factor of five. Features of the chamber include improved water cooling, improved vacuum conductance through copper RF screens featuring over 15,000 small square holes and the ability to sublime titanium while the beam is still on.

STATUS REPORT OF THE PEP-II Movable Collimators

S. DeBarger, S. Metcalfe, C. Ng, J. Seeman, M. Sullivan, U. Wienands
Stanford Linear Accelerator Center (SLAC), CA 94025 Accelerator Group

Three movable collimators have been manufactured for installation in the PEP-II LER and HER beamlines upstream of BaBar to improve backgrounds in BaBar by a factor of 2. Each collimator has a pair of horizontally opposed, water cooled jaws with RF finger seals all around the edge of the jaws ・these seals are the only sliding parts inside the vacuum chamber. Each jaw travels independently through a distance of 16.5mm (LER) and 21mm (HER) and is supported above the collimator from motorized slideways with position feedback. The larger HER collimator has a titanium sublimation pump incorporated into the underside of the collimator, pumping through RF screens in the bottom of the chamber. Water cooled fixed ramps protect the leading and trailing edges of the jaws.

THE TESTA CRYOGENIC ACCELERATOR MODULES

C. Pagani, D. Barni, M. Bonezzi, P. Pierini
INFN Milano-LASA, Milano, Italy
R. Bandelmann, G. Grygiel, K. Jensch, R. Lange, A. Matheisen, W.-D. Moeller, H.-B. Peters, B. Petersen, J. Sekutowicz, D. Sellmann, S. Wolff, K. Zapfe
DESY, Hamburg, Germany

The design of TESLA, that is the superconducting option for the next generation e+e- TeV Collider, is in its final stage and takes advantage of the experience gained through the TESLA Test Facility (TTF), in operation at DESY in the framework of a wide International Collaboration. The 32 km long TESLA needs for acceleration more than 21,000 Nb 9-cell superconducting cavities at 1.3 GHz. These cavities, individually equipped with a Ti helium vessel, RF couplers, tuner and magnetic shielding, are assembled, for operation at 2 K, in groups of 12 in16 m long cryomodules. To minimize the static losses, 2 thermal shields are used, at 5-8 K and 40-80 K respectively, and the 2 K helium gas return line acts as supporting beam for the active elements. Static losses at 2K as low as 0.2 W/m, together with the respect of the required alignment tolerances, have been proven at TTF. About one third of the cryomodules, with increased length, will include the required superconducting quadrupoles and steering coils, while just one tenth of them will be equipped with cryogenic valves and instrumentation for cool down and warm up purposes. This paper presents details of the design, construction and assembly of the TESLA cryomodules which are based on the outstanding results obtained with the 12 m long cryomodules of TTF.

The Cryogenic System of TESLA

Siegfried Wolff, for the TESLA Collaboration
DESY

The Tera-eV Energy Superconducting Linear Accelerator (TESLA) is a 32 km long superconducting linear collider of 500 GeV (upgradeable to 800 GeV) centre of mass energy, presently in the planning phase at DESY. It will consist of about 21000 superconducting RF 9-cell cavities of pure Niobium, each of about 1 m length, cooled in a 2.0 K helium bath and operated at 1.3 GHz with 5 Hz beam repetition rate. The cavities, equipped with their individual helium vessels made from titanium, will be assembled in about 16 m long cryostats (cryomodules) with thermal radiation shielding at 5-8 K and 40-80 K. Part of the cryomodules will also be equipped with superconducting quadrupoles and steering coils. The roughly 1800 cryomodules, arranged in 12 underground accelerator sections (cryogenic units) of about 2.5 km length, will be cooled from 7 cryogenic halls distributed along the whole length of the collider. The first part of the collider, declined by 8 milliradian before becoming horizontal, will also be used as an accelerator for a Free Electron Laser (FEL), a brilliant X-ray facility with a wavelength down to 0.1 nm. The total design refrigeration capacity will be about 30 kW at 2 K, 52 kW at 5-8 K and 565 kW at 40-80 K. A proposal for approval of the project including the Technical Design Report (TDR) and cost estimates is being prepared. The paper will present the cryogenic system starting with the design of the cryomodules, followed by a description of the cryogenic distribution within the cryo-units and a description of the layout of the cryogenic plants.

Photon colliders: current and future projects

Valery Telnov
Institute of Nuclear Physics, Novosibirsk

High energy photon colliders based on backward Compton scattering of laser light is a very natural additional option for e+e- linear colliders. It is considered now for current LC project: NLC, JLC, TESLA, CLIC. The expected number of interesting events in gamma-gamma collisions will be not less than in e+e- collisions. Photon colliders are the best for study of many physics phenomena. The luminosity at photon colliders in the current designs is determined by ``geometric luminosity'' of ee collisions. Having beams with smaller emittances one can obtain more than one order higher luminosity. Especially attractive is a Higgs factory (if the Higgs with mass 100-200 GeV is really exist). In this talk we discuss current projects of photon colliders, accelerator problems for the Higgs (WW and other) factories, problems of multi-TeV photon colliders.

RECENT PROGRESS IN THE ACCELERATOR TEST FACILITY AT KEK

Kiyoshi Kubo for ATF Collaboration
KEK, Accelerator Laboratory

The Accelerator Test Facility (ATF) at KEK is a test accelerator for future linear colliders. Its purpose is to test the feasibility of the production of multibunch beams with extremely low transverse emittances. It consists of a high gradient S-band linac, a beam transport line, a damping ring and an extraction line. Until this summer the main target had been to produce low emittance beams with single bunch operation. We confirmed the small horizontal emittance, 1.4 nm-rad[1], which agrees well with the design value. On the other hand, producing and measuring the low vertical emittance have not been easy. Our target is 1% of the horizontal emittance which corresponds to the typical beam size of about 8 micron. We will report tuning of the damping ring for the low vertical emittance and the emittance measurement in the damping ring and in the extraction line. From November 2000, multibunch operation will be another main task of ATF. A bunch train consists of 20 bunches is produced, accelerated in the linac, injected in the damping ring and extracted to the extraction line. Uniformity of bunch to bunch population, bunch to bunch energy difference, flatness of the kicker strength for injection and extraction, beam loading in the damping ring RF cavities and bunch by bunch instrumentation will be main issues. Technical development and experimental results of the multibunch operation will be reported.

Developments on Computation and Measurements of HOM In X-Band Accelerator Structure

Wei Shi,Lin Yuzheng,Xiao Liling,Liang Yuzhong
Department of Engineering Physics,Tsinghua University

A 2.5D RF cavity code is developed with the quadratic vector finite elements method, which can precisely evaluate all the eigenfrequencies and fields for symmetric cavities. Additionally, the singular points are also considered, which efficiently improve the precision of the results. It is used to compute high order modes (HOM) in accelerator cavities of next linear collider. Expected results are available. Meanwhile, a perturbation method is improved on the measurements of X-Band detuned structure of KEK. A metallic cage made by sputtering silver film onto a thin nylon thread through a specially designed fixture is used as perturbing object. This type of perturbation object has high sensitivity and high resolution. With this method, the longitudinal electric fields of TM110 modes in an X-Band 30cm structure are measured.

STATUS OF THE X-BAND RF POWER SOURCE DEVELOPMENT FOR JLC

Yong Ho Chin, Mistuo Akemoto, Pavel Jogolev, Shuji Matsumoto, Hajime Mizuno, Yuichi Morozumi, Keiji Ohya, Koji Takata, Nobu Toge, Shuichi Tokumoto, and Seiya Yamaguchi
KEK, Tsukuba, Japan
Vladimir Balakin, Sergey Kazakov, Anderei Larionov, Vladimir Teryaev, Vladimir Vogel
BINP, Protvino, Russia
Karen Fant, Chris Nantista, Sami Tantawi, Arnold Vlieks
SLAC, USA

In this paper, we summarize the status of X-band RF power source development for the Japan Linear Collider (JLC) project. The periodic permanent magnet (PPM) klystrons are under development in the two-year/two-stage project with Toshiba. The goal is to produce 50MW output power at 1.5 micro-sec pulse length at the first klystron and then to advance to 75MW at the second one. The high power testing of the first klystron was carried out successfully and its goal was well achieved. The multi-mode RF windows have been high power tested at KEK and SLAC. The window with smaller diameter (53mm) achieved a circulation power of 80MW with 1.5ms duration at 30Hz repetition. It was not destroyed during the testing. As for the modulator, the SI-thyristor solid state switches were tested successfully. KEK is developing the multi-mode 2x2 DLDS (Delay Line Distribution System) power distribution system, in which the stability of linearly polarized TE12 mode in a long (up to 160m) waveguide is the key for low loss power transport. The experiment was carried out successfully in the ATF linac tunnel in collaboration with SLAC using a specially installed 55m long waveguide. Details of these developments and measurement results are presented.

A Shaky Road to Subnanometer Beams. NLC Ground Motion, Vibration and Stabilization Studies.

Andrei Seryi
Stanford Linear Accelerator Center

Ground motion and vibration are major concerns for the next generation of high energy accelerators, particularly for e+e- linear colliders like the NLC. This has led to a renewed interest worldwide in modeling and measuring these effects. The 22nd Advanced ICFA Beam Dynamics Workshop on Ground Motion in Future Accelerators was held recently at SLAC. This paper summarizes the results from that workshop and presents the comprehensive model of ground motion being developed for the NLC. The model is compared with recent measurements and the implications for a multi-TeV collider are discussed.

Next Linear Collider Layout

Nan Phinney
SLAC for the NLC Design Group

The layout of the Next Linear Collider (NLC) has been revised to provide greater physics capabilities and to make the design more cost effective. The injector complex has been centralized to reduce cost and provide more flexibility for future upgrade scenarios, such as two-beam acceleration. The basic rf unit for the main linacs uses a solid-state modulator to drive 8 70 MW klystrons with a 3 microsecond pulse length. The rf power is distributed with a multi-mode Delay Line Distribution System (DLDS) to 16 girders of accelerating structures. This configuration improves the AC to rf efficiency while reducing the number of modulators and klystrons required by a factor of two. Using a new compact design for the final focus, the NLC now has two different Interaction Regions (IR), one for high energy (250-1000 Gev cms) and one for low energy (90-350 Gev cms). The high energy IR has minimum bending to support an eventual upgrade to 3-5 Tev cms. The low energy IR is optimized for the precision studies at the Z-pole, Top and possibly Higgs threshold. The design allows for beam to be shared between the two IRs and the possibility of 180 hz operation is under study. The present design provides flexibility for a variety of upgrade and staging scenarios from initial operation at low energy to a future extension to multi-Tev.

Post-Linac Collimation for Future Linear Colliders: Challenges and Solutions

P. Tenenbaum for the NLC Collimation Task Force
SLAC, NLC Project

The post-linac collimation system for a high-energy, high-luminosity linear collider must remove high-amplitude particles which would cause unacceptable detector backgrounds, while simultaneously preserving the quality of the beam. It must also protect the final focus and detector from mis-steered or off-energy bunch trains without being destroyed. These tasks are made more difficult by the high power density and low repetition rate of the beam, as well as the beam-dynamics consequences of small-aperture collimators. We describe the obstacles to successfully achieving the goals described above, and detail some solutions which permit an acceptable compromise design for the collimation system, with examples from extant linear collider projects. We discuss the ongoing experiments to clarify significant remaining unknowns, in particular the measurements of transverse wakefields of longitudinally-tapered collimators.

Cavity R&D for TESLA

Lutz Lilje
DESY -FDET- for the TESLA Collaboration

The talk will review the cavity research and development which was essential to achieve the performance goals of a Q0 of 10^10 at an accelerating gradient of 23,5 MV/m for TESLA500. Results from the 1,3 GHz nine-cell superconducting niobium cavities will be shown. For TESLA800 the specifications are a Q0=5*10^9 for the accelerating gradient of 35 MV/m. It will be shown that this is achieved regularly in electropolished one-cell cavities. First promising results on nine-cell cavities are shown. Very interesting results on the cavity production with hydroforming and spinning will be shown. For TESLA800 it is necessary to increase the fill factor of the linac. This achieved via the superstructure concept. First results on the superstructure cavities will be shown.

Achievements and future plans of CLIC Test Facilities

Hans-H. Braun
CERN, Geneva, Switzerland

CTF II has been originally designed to demonstrate the feasibility of two beam acceleration with high current drive beams and a string of 30 GHz CLIC accelerating structure prototypes (CAS). This goal has been achieved in 1999 and the facility has been modified to focus on high gradient testing of CAS's and 30 GHz single cell cavities (SCC). With these modifications it is now possible to provide 30 GHz RF pulses of more than 150 MW and a pulse-length adjustable from 2-15 ns. While the SCC results are promising, the testing of CAS's revealed problems of RF break-down and related surface damage for relative low accelerating gradients. As a consequence a new R&D program has been launched to advance the understanding of RF break-down processes, to improve the material and surface properties of the CAS's and to optimise the structure geometries. In parallel to these activities the construction of a new facility named CTF3 has started. CTF3 mainly serve two purposes. The first is the demonstration of the CLIC drive beam generation scheme. CTF3 will accelerate a 1540 ns long electron pulse of 3.5 A in a fully beam-loaded S-band linac. The linac beam pulse is compressed in isochronous rings to 140 ns pulse- length, 35 A beam current and a micro-bunch repetition rate of 15 GHz. The second purpose of CTF3 is to test CAS's with nominal CLIC parameters, in particular with the nominal pulse-length. For that reason the drive beam extracted from the combiner ring is transported through a string of 30 GHz power extraction cavities feeding a string of CAS's. The 30 GHz acceleration is measured with a probe beam provided by a small, separate S-band linac.

Final-focus schemes for CLIC at 3 TeV

H. Burkhardt, S. Fartoukh, F. Zimmermann
CERN, SL Division, 1211 Geneva 23, Switzerland

We discuss benefits and drawbacks of different final-focus
schemes for CLIC at 3 TeV CoM energy, by examining tolerances, tunability and potential background for a conservative 3-km long final-focus system [1] and for shorter advanced designs [2,3]. [1] F. Zimmermann, R. Assmann, G. Guignard, D. Schulte, O. Napoly, "Final-Focus System for CLIC at 3 TeV", Proc. EPAC 2000, p. 519. [2] S. Fartoukh and J.B. Jeanneret, "Using microwave quadrupoles to shorten the CLIC beam delivery section", Proc. EPAC 2000, p. 480. [3] P. Raimondi and A. Seryi, "A Novel Final Focus Design for High Energy Colliders", Proc. EPAC 2000, p. 492.

Multi-bunch generation by thermionic gun

KURIKI Masao, HAYANO Hitoshi, and NAITO Takashi
KEK, Accelerator lab.

KEK-ATF is studying the low-emittance multi-bunch electron beam for the future linear collider. In ATF, thermionic gun is used to generate 20 bunch electron beam. Due to a distortion on gun emission and beam loading effect in the bunching system, the intensity for each bunch is not uniform by up to 40 % at the end of the injector. We have developed a system to correct the gun emission by precisely controlling the grid voltage with a function generator. For the beam loading effect, we have introduced an amplitude modulator on Sub Harmonic Buncher, SHB RF. An uniform multi-bunch beam will be obtained by these modifications.

The TESLA Cryogenic Distribution System

Siegfried Wolff, Holger Lierl, Bernd Petersen
DESY
Hans Quack
TU Dresden

The Tera-eV Energy Superconducting Linear Accelerator (TESLA), a 32 km long superconducting linear electron/positron collider of 500 GeV (upgradeable to 800 GeV) centre of mass energy, presently in the planning phase at DESY, will consist of about 1800 cryomodules, each containing 12 superconducting RF 9-cell cavities of pure niobium. About 800 cryomodules also contain a superconducting quadrupole magnet and one or two dipole correction coils. The cavities, operated at 1.3 GHz with 5 Hz beam repetition rate, as well as the magnets have to be cooled in a 2.0 K superfluid helium bath. They are housed in individual helium vessels made from titanium. The cryomodules are equipped with thermal radiation shielding at 5-8 K and 40-80 K.
The 32 km long chain of cryomodules is split into 12 cryogenic units of about 2.5 km length. Each unit is supplied with helium from one end by a refrigerator. Part of the 2.2 K, 1.2 bar helium stream from the refrigerator is expanded in a Joule-Thomson valve into a two-phase supply line at every 10th cryomodule. The liquid fraction is filling the helium vessels whereas the vapour returns at ~ 31 mbar pressure to the refrigerator through a 300 mm diameter gas return pipe inside the cryomodules. The paper describes the layout of the cryogenic distribution, the cooling scheme and the different operating modes, presents the overall heat load budget including safety margins and discusses the consequences of an energy upgrade.

The TESLA Cryo-Plants

Hans Quack
TU Dresden
Holger Lierl, Bernd Petersen, Siegfried Wolff
DESY

The Tera-eV Energy Superconducting Linear Accelerator (TESLA) is a 32 km long superconducting linear electron/positron collider of 500 GeV centre of mass energy (upgradeable to 800 GeV), presently in the planning phase at DESY. About 21000 superconducting RF 9-cell cavities, made of pure Niobium and operated at 1.3 GHz with 5 Hz beam repetition rate, have to be cooled with superfluid helium at 2 K. The cavities are assembled in groups of 12 into about 16 m long cryo-modules. A fraction of cryomodules also contains superconducting quadrupoles and correction dipoles. The roughly 1800 cryomodules are arranged in an underground accelerator tunnel in 12 about 2.5 km long cryo-units. Except for the 2 first cryo-units every 2 cryo-units will be supplied from one refrigerator in a refrigerator hall above ground. The first two cryo-units, which are used also for a Free Electron Laser, a brilliant X-ray facility of a wavelength down to 0.1 nm, have individual refrigerators in individual refrigerator halls. The design refrigeration capacity of each of the 7 refrigerators for 500 GeV will be about 4.2 kW at 2 K, 7.4 kW at 5-8 K and 80.7 kW at 40-80 K. More than 70% at 2 K are dynamic loads from the RF. The paper will concentrate on the technology of large helium refrigerators, plant size, reliability and redundancy, and will discuss a model refrigerator as well as the layout of the refrigerator halls including the possible upgrade for 800 GeV operation.

DEVELOPMENT OF 200 KeV POLARIZED ELECTRON SOURCE

K.Wada, M.Yamamoto, T.Nakanishi, S.Okumi, T.Gotou, K.Togawa, C.Suzuki, F.Furuta, T.Nishitani, J.Watamabe, S.Kurahashi and N.Miyamoto
Department of Physics, Nagoya University, chikusa-ku, Nagoya 464-8602, Japan
H.Matsumoto, Y.Takeuchi, M.Yoshioka
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan

A 200 keV polarized electron source with a load lock system was designed to satisfy the requirements of JLC. The components of this system were already constructed. The performances of dark current reduction and clean surface preparation of superlattice photocathode will be reported.

New concept of NLC positron source

Victor P. Belov, Vladimir N. Karasyuk, Valery V. Kobez, Gennady S. Krajnov, Pavel V. Martyshkin, Mikhail V. Petrichenkov, Gregory I. Silvestrov, Alexander N. Skrinsky, Tamara V. Sokolova and Tatiana A. Vsevolozhskaya
Budker Institute for Nuclear Physics, Novosibirsk, Russia

The project of new system for positron generation at NLC is presented, based conceptually on the use of target of liquid lead, fast pumped through, so that the exchange of target matter takes place during one cycle by operation at 120 Hz repetition rate. By this the problem of target survival under up to 250 J/g specific energy deposition is solved together with the problem of removal of 40 kW power, released in the target. Positron collection is fulfilled with the cone shape magnetic concentrator with pulsed field up to 13T. The target end is put in the concentrator aperture to be disposed at the field maximum. An analysis of collection efficiency is presented in dependence on magnetic field, target position, electron beam size and so on, together with the thermal regime and mechanical stresses analysis in target material and in the outlet window, made of diamond- like material cNB. The design is described of the target station with three automatically removable targets.

Development of High Power X-band Semiconductor Microwave Switch for Pulse Compression Systems of Future Linear Colliders

Fumihiko Tamura and Sami G. Tantawi
SLAC

We describe the development of semiconductor X-band high-power RF switches as a mean of high-power RF pulse compression systems for future linear colliders. The switch consists of two 3-dB hybrids and several active modules. Each module is composed of several active elements. The active elements consist of symmetrical three-port tee-junctions and an active waveguide window in the symmetrical arm of the tee-junction. We present the design methodology and the architecture of the whole switch systems. We state the scaling laws that govern the relation between the power handling capability and the number of elements. We designed and built these active waveguide windows. The waveguide window is a silicon wafer with an array of four hundred PIN/NIP diodes covering the surface of the window. This waveguide window is located in an over-moded TE01 circular waveguide. The results of high power RF experiments of the active waveguide window are presented. The experiment is performed at power levels of a few megawatts at X-band. Finally, we discuss further improvement of the active window. These should improve switching speed and high power handling capabilities.

Conceptual Design of JLC Bunch Compressor System

Toshiyuki OKUGI, Kiyoshi KUBO and Masao KURIKI
Accelerator Laboratory, High Energy Accelerator Research Organization (KEK)

The requirement of the JLC bunch compressor system is to compress the bunch from a few mm to 80-150 micron after the damping ring, keeping the small emittance. The present JLC design is required to change the bunch length from 80 to 150 micron rms. at the entrance of the main linac. Therefore, bunch compressor system was redesined to change the final bunch length more flexibly. Furthermore, the emittance dilution was calculated with a tracking code. The main source of the horizontal emittance dilution is the aberation of dispersive system in the bending system by coherent radiation. Vertical emittance dilution is generated by the wake field in the accelerating structures. With the new design, the final bunch length can be changed from 80 to 150 micron with 10% of the emittance dilution for both horizontal and vertical plane in the bunch compressor system.

Performance Study of Double Kicker System in ATF

Takayuki Imai
Science University of Tokyo
Hitoshi Hayano,Junji Urakawa and Nobuhiro Terunuma
KEK

KEK/ATF is an accelerator test facility for an injector part of a future electron-positron linear collider.The key technology in the part is to generate ultra-low emittance multi-bunch beam and to supply stable beam to the main linac for high luminosity. A double kicker was developed in ATF for stable beam extraction from damping ring.The system consists of one pulse power supply and two identical kicker magnets. The kick angle variation of the first kicker in damping ring is compensated with the second one separated by phase advance pi in the extraction line. In this paper, the performance study of the system is described by the analysis of the orbit measurement in the extraction line using strip-line BPMs, wire scanners and cavity BPMs in a single bunch operation. The performance study result for the multi-bunch beam extraction will also be presented.

Processing Studies of X-Band Accelerator Structures at the NLCTA

Chris Adolphsen, William Baumgartner, Keith Jobe, Rod Loewen, Doug Mccormick, Marc Ross, Tonee Smith and Juwen Wang
SLAC
Toshiyasu Higo
KEK

In the current design of the NLC, the linacs will contain roughly 5000, 1.8 m long X-Band accelerator structures that will accelerate beams of electrons and positrons to 250 GeV. These structures will be powered with 170 MW, 380 ns long rf pulses that will produce an average unloaded gradient of 72 MV/m in the structures. As part of the R&D effort for the NLC, a number of prototype structures have been built and rf processed at the Next Linear Collider Test Accelerator (NLCTA) at SLAC. Here it was found that the net rf phase advance through the structures increased by roughly 10 degrees per 500 hours of operation at gradients of 40 MV/m to 75 MV/m. The phase changes occurred mainly in the front ends of the structures where the rf group velocity is highest (the cell irises are heavily pitted here as well). To understand this phenomenon, a series of structures with different group velocities and lengths will be processed to compare performance. In addition, efforts are being made to reduce contaminates in future structures and to find methods of processing that yield less damage. This paper presents results from these studies.

Collective Beam-Beam Effects in Hadron Colliders

Jack Shi and Lihui Jin
Department of Physics & Astronomy The University of Kansas Lawrence, KS66045

The strong-strong beam-beam effects in hadron colliders were studied on LHC including multipole field errors in the lattice and beam-beam interactions at two high-luminosity interaction points. The study was conducted with tracking of one million particles over 100 thousand turns by using the particle-in-cell method. It was found that when the beam-beam parameter exceeds a threshold, a beam-beam instability characterized by an unstable oscillation of beam centroids and an enhanced beam-size growth occurs. After the onset of the beam-beam instability, the transverse-phase-space area nearby origin (closed orbit) becomes unstable for beam centroids and two initially centered counter-rotating beams develop a spontaneous unstable off-center oscillation. The dynamics of the unstable beam-centroid oscillation has typical characteristics of chaotic transport in phase space. A study of the dynamics of beam tune spread calculated during the self-consistent beam-beam simulation showed that after the onset of the beam-beam instability, particles in beam cores cross the 2nd-order difference resonance, which drives particles from the beam core to beam tails and results in the enhanced beam-size growth. Such the beam-beam instability could be effectively suppressed by an elimination of the centroid motion with feedback. The study also showed that the actual beam tune spread due to beam-beam interactions of hadron beams deviates significantly from that calculated with strong-weak beam-beam tracking. The beam-beam linear tune shift or tune footprint calculated with the assumption of Gaussian distribution of beams may therefore not be good indicators for the beam-beam instability of hadron beams.

VLHC Based on a Cooled Iron Intermediate Field Superconducting Magnets

Alexander D. Kovalenko
Joint Institute for Nuclear Research, Laboratory of High Energies

New approach to the VLHC design is considered. The magnets are based on a superconducting single layer winding at T=4.5K and iron yoke/shield at T=50-80K. The experimental results obtained at the Laboratory of High Energies of JINR in this direction are presented. The essential features of the modified Nuclotron-type and cosine theta magnets are analized. The other key problems of the VLHC conctruction are also discussed.

PERFORMANCE OF THE LHC PRE-INJECTORS

M. Benedikt, R. Cappi, M. Chanel, R. Garoby, M.Giovannozzi, S. Hancock, M. Martini, E. Metral, G. Metral, K. Schindl, J.L. Vallet.
CERN, Geneva, Switzerland

The LHC pre-injector complex, comprising Linac 2, the PS Booster and the PS, has undergone a major upgrade in order to meet the very stringent requirements of the LHC. Whereas bunches with the nominal spacing and transverse beam brightness were already available from the PS in 1999, their length proved to be outside tolerance due to a debunching procedure plagued by microwave instabilities. An alternative scenario was then proposed based on a series of bunch-splitting steps in the PS. The entire process has recently been implemented successfully, and beams whose longitudinal characteristics are safely inside LHC specifications are now routinely available. Variants of the method also enable bunch trains with gaps of different lengths to be generated. These are of interest for the study and possible cure of electron cloud effects in both the SPS and LHC. The paper summarizes the beam dynamics issues that had to be addressed to produce beams with all the requisite qualities for the LHC.

Coherent beam-beam effects in the LHC

Werner Herr, Hans Grote and Maria-Paz Zorzano
CERN
Yuri Alexahin
DUBNA

In the Large Hadron Collider (LHC) two proton beams of similar intensities collide in several interaction points. It is well known that the head-on collision of two beams of equal strength can excite coherent modes whose frequencies are separated from the incoherent spectrum of oscillations of individual particles. This can lead to the loss of Landau damping and possibly to unstable motion. The beam-beam effect in the LHC is further complicated by a large number of bunches (2808 per beam), a finite crossing angle and gaps in the bunch train. The coherent beam-beam effects under various conditions and operational scenarios are studied analytically and with multiparticle simulations. We give an overview of the studies and present proposals to overcome these difficulties together with possible side effects.

Studying rigid bunch oscillations in the LHC with strong-strong beam-beam interactions for many bunches

Hans Grote
CERN, SL Division

In part of the straight sections of the LHC the two beams share a common beam tube. Therefore the bunches cross each other not only at the interaction point, but as well at many places on either side, with a typical transverse separation of 10 times the transverse beam size. These "parasitic" encounters lead to orbit distortions and tune shifts, in addition to higher order effects. Since the string of bunches from the injection machine contains gaps, not all possible 3564 "buckets" around the machine are filled, but only 2808. This in turn causes some bunches to not always encounter bunches in the opposite beam at one or several parasitic collision points (so-called "pacman" bunches), or even at the head-on interaction point ("super-pacman" bunches). With a special program self-consistent orbits in the LHC have been calculated for the first time with the full beam-beam collision scheme. All ca. 6000 bunches are then tracked for 10000 turns with different initial conditions. Results comprise closed orbit off-sets, higher-mode spectra, and energy spreading between bunches.

Status Report for RUN II at Fermilab

Ioanis Kourbanis
FNAL

Ongoing upgrades for the Tevatron together with the operation of the new Main Injector and the Recycler Ring will allow an unprecedented Luminosity. The status of the various pre-injectors, the Tevatron itself and plans for future upgrades to allow a final integrated Luminosity of 15 inverse Femtobarn will be presented.

THE LARGE HADRON COLLIDER - PRESENT STATUS AND PROSPECTS

Lyndon R. Evans
European Organization for Nuclear Research (CERN), DG

The Large Hadron Collider (LHC), due to be commissioned in 2005, will provide particle physics with the first laboratory tool to access the energy frontier above 1 TeV. In order to achieve this, protons must be accelerated and stored at 7 TeV, colliding with an unprecedented luminosity of 1034 cm-2 s-1. The 8.3 Tesla guide field is obtained using conventional NbTi technology cooled to below the lambda point of helium. Considerable modification of the infrastructure around the existing Large Electron Positron (LEP) collider tunnel is needed to house the LHC machine and detectors. The project is advancing according to schedule with most of the major hardware systems including cryogenics and magnets under construction. A brief status report is given and future prospects are discussed.

Simulation of a Realistic RF System with Beam in a Synchrotron

Joachim Tuckmantel
CERN, SL-HRF

Due to heavy beam loading with gaps in the new Large Hadron Collider (LHC), RF and beam are intimately linked as a complex system with fast transients and the details of the RF system and its limitations play a decisive role. With analytical methods overall system stability of such a system is difficult to assess and the definition of RF components is delicate. Therefore the author has written a simulation program modeling RF feedback with its loop-delay, transmitter power limitation and limited amplifier bandwidth as well as one-turn-delay feedback and longitudinal damping of freshly injected batches. The program was applied to the LHC with its double RF system and its beam with bunch trains and sub-trains. Development of all RF and beam quantities is displayed graphically online at regular intervals. These frames are saved in parallel and can be assembled to produce a realistic movie as would be seen operationally in future on a color multi-trace scope in the LHC control room.

Test results of the LHCIRQ 1-m model magnets, quench and mechanical performance

T. Nakamoto, T. Ogitsu, Y. Ajima, E. Burkhardt, N. Higashi, M. Iida, N. Kimura, H. Ohhata, N. Ohuchi, T. Shintomi, K.Sugita, K. Tanaka, A. Terashima, K. Tsuchiya, and A. Yamamoto
High Energy Accelerator Research Organization (KEK)

A development of 70 mm aperture superconducting quadrupole magnets for LHC low-beta insertion is under way at KEK. The development is a part of the collaboration between KEK and CERN for LHC, and sixteen 6-m long magnets will be installed in the insertion region of the LHC. After the R&D of the three 1-m long model magnets, the fourth 1-m model magnet was produced, in order to confirm the performance of the final cross section. The fifth, identically designed, model magnet was also built at a company to confirm the technical transfer to the company. These magnets were tested at KEK cryogenics science center using a vertical cryostat. The magnets were connected in series and excited simultaneously. Quench performance, mechanical behavior and field quality were measured. The paper reports the quench performance and mechanical behavior. The field quality will be reported in the other paper submitted in the same conference.

Field quality of the LHC-IRQ 1-m model quadrupole magnets developed at KEK

N. Ohuchi, Y. Ajima, Y. Hirano, T. Nakamoto, T. Ogitsu, T. Shintomi, K. Tsuchiya and A. Yamamoto
High Energy Accelerator Research Organisation (KEK)

As a part of the collaboration program between CERN and KEK, sixteen 6-m long superconducting quadrupole magnets will be constructed for the interaction region of LHC. During the R&D process of these magnets, five 1-m model quadrupoles have been constructed. The field measurements were performed at 1.9 K with the rotating harmonic coils: 200 mm and 600 mm long harmonic coils for the integral field and a 25 mm long harmonic coil for the fine field profile along the magnet ends. After the magnetic field measurements of the first two models, the magnet cross section was optimised and redesigned to satisfy the requirement for field harmonics by the beam optics study. The successively fabricated three models, one of which was made for technical transfer to a company, have shown field harmonics within the required tolerance and their reproducibility. In this paper, we will summarise the magnetic field quality among these five magnets.

AN ENERGY-RECOVERY ELECTRON LINAC-ON-PROTON RING COLLIDER

Lia Merminga, Geoffrey A. Krafft and Valeri A. Lebedev
Jefferson Laboratory, Accelerator Physics Department

Electron-proton colliders with center of mass energies between 14 GeV and 100 GeV and luminosities at the 10e33 level have been proposed recently as a means for studying hadronic structure. Electron beam polarization appears to be crucial for the majority of experiments. Two accelerator design scenarios have been examined in detail: colliding rings and recirculating linac-on-ring. Although the linac-on-ring scenario is not as well understood as the ring-ring scenario, comparable luminosities appear feasible, while the linac-on-ring option presents a significant advantage with spin manipulations. Rf power and beam dump requirements make the linac-on-ring option viable only if the electron linac recovers the beam energy, a technology demonstrated at Jefferson Lab's IR FEL, with cw current up to 5 mA and beam energy up to 50 MeV. Based on extrapolations from actual measurements and calculations, energy recovery is expected to be feasible at higher currents (a few hundred mA) and higher energies (a few GeV) as well. We begin with a brief overview of Jefferson Lab's experience with energy recovery and summarize its benefits. Luminosity projections for both scenarios based on fundamental limitations are presented next. The feasibility of an energy recovery electron linac-on-proton ring collider is investigated and three conceptual point designs are shown. Accelerator physics issues are discussed and a list of required R&D for the realization of such a design is presented.

Future HERA High Luminosity Performance

Georg H. Hoffstaetter and Ferdinand Willeke
DESY Hamburg, Germany

The interaction regions of the HERA e-p collider are being equipped with new quadrupole and dipole magnets to allow for smaller beta functions at the two interaction points (IPs). This is expected to decrease the beam cross section at the IP and thus increase the luminosity by a factor of 4 to a nominal value of 7 times 10 to the 31 per square centimeter and s. However, in order to achieve this high luminosity the beam-beam tune shift values of the e-beam have to be increased, the emittances of the e-beam have to be decreased, and the vertical beta function of the protons have to become comparable to the proton bunch length. This implies different beam dynamical conditions compared to the year 2000 operating conditions. In a series of machine experiments, the beam-beam limits of the two HERA beams have been explored. The new low emittance optics has been implemented and tested with a polarized positron beam. Based on these experiences, the performance limitations of the HERA e-p collider after the luminosity upgrade will be discussed.

NEUTRINO FACTORY AND MUON COLLIDER COLLABORATION R&D ACTIVITIES

Michael S. Zisman, for the Neutrino Factory and Muon Collider Collaboration
Center for Beam Physics Accelerator & Fusion Research Division Lawrence Berkeley National Laboratory Berkeley, CA 94720 U.S.A.

The Neutrino Factory and Muon Collider Collaboration (MC) comprises about 140 U.S. and non-U.S. accelerator and particle physicists. The MC is carrying out an R&D program aimed at validating the critical design concepts required for the construction of such machines. At present, the primary thrust of the R&D program is toward the issues critical to a Neutrino Factory facility. The main activities of the MC include a Targetry program, a MUCOOL program, a component development program, and a theory and simulation effort. The Targetry program is aimed at investigating the lifetime performance and muon yield of selected targets in a realistic configuration (including a 20-T solenoidal field) exposed to a MW-level proton beam from the AGS at BNL. The MUCOOL program is aimed at developing and testing the components required to construct a muon cooling channel (high-gradient RF cavities, liquid-hydrogen absorbers, solenoidal focusing magnets), with the ultimate goal of an experimental demonstration of muon cooling. Additional activities include development of a high-gradient superconducting RF cavity operating at about 200 MHz, diagnostics to monitor and control the beam, and an induction linac module with internal superconducting solenoid coil. Complementary theory and simulation efforts in support of the experimental effort are a key part of the R&D program, and have led to the existence of new simulation tools (e.g., ICOOL) and new analytic approaches to solenoidal focusing optics. Lastly, the MC has participated in several feasibility studies for a complete Neutrino Factory facility, with the aim of identifying any additional R&D activities needed to prepare a Zeroth-order Design Report (ZDR) in about three years and a Conceptual Design report (CDR) about two years thereafter. In this paper, the R&D goals in each area will be indicated, and the present status and future plans of the R&D program will be described.

STATUS REPORT ON THE SIX-MONTH STUDY ON HIGH ENERGY MUON COLLIDERS

Bruce J. King
Brookhaven National Laboratory, Center for Accelerator Physics (on behalf of the study participants)

The six-month study to examine the feasibility of high energy muon colliders is nearing completion. A progress report on the study is presented. The structure and parameters of the study are reviewed and the areas of significant progress and results so far are reported.

CURRENT ACTIVITIES FOR A NEUTRINO FACTORY AT CERN

R. Garoby for the Neutrino Factory Working Group
CERN, Geneva, Switzerland

Development is necessary in a large number of technologies before a Neutrino Factory complex can be built. In the case of the CERN project, and with the help of other laboratories, work has started for the proton driver, the target and the focusing, cooling, acceleration and storage of muons. The subjects under investigation and the status of the studies are described.

Linear Beam Dynamics of Transverse and Longitudinal Ionization Cooling

Emittance Exchange between Transverse and Longitudinal Phase Space by Bunch Stacking

Yasuo Fukui
UCLA, Physics and Astronomy Dept.

The emittance exchange scheme between the longitudinal phase space and the transverse phase space was demonstrated in simple models with a precision particle tracking simulation, in order to obtain the high intensity cooled muon beam for the neutrino factory and the mu+mu- collider. The mini muon bunches after the pion production target, the muon phase rotation channel, the bunching section, and the ionization cooling section, are placed together in time by using numerous delay channels, and they are stacked together in the longitudinal phase space. By stacking N mini muon bunches, we obtain the longitudinal phase space reduction of 1/N in maximum, which then be converted into the increased muon transverse phase space by a factor N in minimum by the 6 dimensional phase space conservation. The emittance exchange is a key element to obtain the 10E-5 to 10E-6 phase space cooling in the 6 dimensional muon phase space for the mu+mu- collider, and it can be a key element to reduce the cost of the neutrino factory.

Polarization of the High Intensity Muon Beam for the Neutrino Factory

Yasuo Fukui
UCLA, Physics and Astronomy Dept.
Richard C. Fernow, and Juan C. Gallardo
Brookhaven National Laboratory, Center for Beam Physics

The muon polarization of the high intensity muon beam source for the neutrino factory was simulated from the pion production target to the end of the ionization cooling channel with the spin tracking along the muon source channel. The range of the muon polarization and its correlation to the particle arrival time are given with models of the feasibility studies for the neutrino factory. The muons are 100 % polarized in the rest system of the charged pions which are generated in the interaction of high intensity protons in a target. Because of the Lorenz boost with the pion in the laboratory system, average polarization of the muons obtain non-zero average value, if we capture all the muons in the pion decay. In a process of the pion capture with a field decreasing solenoid and the phase rotation with induction linac channels or RF cavity channels, the energy width of the pions and muons are minimized, and a part of the muons in the pion decay is accepted into the bunching and the ionization cooling channel. The muon polarization was tracked through the electro-magnetic fields and through absorbers of the ionization cooling. The strength of the muon polarization and its correlation to the particle arrival time is a figure of merit parameter besides the ratio of the number of muons at the end of the ionization cooling channel to the number of primary protons into a target, in the design of the muon beam source for the neutrino factory.

Toward Neutrino Factory -- FFAG accelerators for muon beam acceleration

Yoshiharu Mori, Shinji Machida, Kiyomi Koba, Takeichiro Yokoi
KEK
Y. Iwashita
Kyoto University

Muon acceleration and storage for Neutrino Factory require new ideas and R&Ds in many fields of accelerators. As a possible alternative to a "conventional" scheme of acceleration of muon beams with staged accelerators of high frequency linacs, we have proposed the entire accelerator chain replaced with a Fixed Field Alternating Gradient (FFAG) machine. Because of a huge acceptance and ultra-high gradient of low frequency rf, the FFAG option　simplifies the whole layout and becomes cost effective. In this scheme, the elements like a transverse and longitudinal cooling and a matching section between adjacent machines could be eliminated. In this paper, we will show the conceptual design of a Neutrino Factory and other facilities, for example PRISM, based on a FFAG machine. In addition, ongoing R&Ds essential to realize those facilities such as a low frequency rf cavity with ultra-high gradient, a proof of principle model of the FFAG acceleration, and high field kickers will be presented.

STATUS REPORT ON STUDIES FOR NEUTRINO FACTORIES AND MUON COLLIDER

Alessandra M. Lombardi
PS division CERN

The physical and technical issues will be summarised and the results from theoretical studies and experimental activities presented. Possible R&D programmes towards the realisation of Neutrino Factories and Muon Colliders will be discussed.

Beam-beam interaction in a muon collider ring

Eun-San Kim and Moohyun Yoon
Pohang Accelerator Laboratory, POSTECH, San 31, Hjoja Dong,
Pohang, Kyungbuk, Korea, 790-784

The effect of a beam-beam interaction in a muon collider ring is investigated by a weak-strong model. In the degign of the muon collider ring, the slippage factor is approximately 0.000001. This may lead to an increase in the energy spread due to the beam-beam interaction. Through the simulation, we have investigated parametric dependencies of the induced energy spread due to the beam-beam interaction. Beam-beam effects on the transverse beam size are also shown.

Comparison of cooling channels for a neutrino factory

Eun-San Kim and Moohyun Yoon
Pohang Accelerator Laboratory, POSTECH, San 31, Hjoja Dong,
Pohang, Kyungbuk, Korea, 790-784

Parameters and performances of transverse muon cooling channels are compared:(1) FOFO, (2) DFOFO, (3) Super-FOFO and (4) Alternating solenoid cooling channels. Transverse cooling results are also compared with those of analytical method, which show good agreements. We also show the results on fundamental design for emittance exchange.

High Frequency Phase-Energy Rotation for Muons

David Neuffer
Fermilab
Robert Palmer
BNL

An alternative scenario for bunching and phase-energy rotation of muons from a proton source target is presented. It consists of a drift section, a variable frequency 300 to 200 MHz bunching section and a fixed frequency (~200 MHz) z-dE rotation section. The total rf required for the system is quite modest, and performance can be similar to that of induction linac + buncher systems developed for muon storage ring neutrino factory studies.

Quantum Mechanical Treatment of Transit-Time Optical Stochastic Cooling of Muons

A.E. Charman
Department of Physics, U.C. Berkeley
J.S. Wurtele
Department of Physics, U.C. Berkeley Center for Beam Physics, Lawrence Berkeley National Laboratory

Fast stochastic cooling (i.e., on microsecond time-scales) would be desirable in certain applications, for example, to boost final luminosity in the proposed muon collider, where the short particle lifetime severely limits the time available to reduce beam phase space. But fast cooling requires very high-bandwidth amplifiers so as to limit the incoherent heating effects from neighboring particles. A method of transit-time optical stochastic cooling has been proposed which would employ high-gain, high-bandwidth, solid-state lasers to amplify the spontaneous radiation from the charged particle bunch in a strong-field magnetic wiggler. This amplified light is then fed back onto the same bunch inside a second wiggler, with appropriate phase delay to effect cooling. But before amplification, the usable signal from any one particle is quite small, on average much less than one photon for each pass through the wiggler, suggesting that the radiation must be treated quantum mechanically, and raising doubts as to whether this weak signal even contains sufficient phase information required for cooling, and whether it can be reliably amplified to provide cooling on each pass. A careful treatment of the dynamics, where the radiation and amplification processes are treated quantum mechanically, indicates that fast cooling is in principle possible, with cooling rates which essentially agree with a simple classical calculation, provided that the effects of the unavoidable amplifier noise arising from quantum mechanical uncertainty are included. Thus, quantum mechanical uncertainties do not present any insurmountable obstacles to optical cooling, but do establish a lower limit on cooling rates and achievable emittances.

The resonant multi-gap funnelling and de-funneling systems

Yu.Senichev and W.Braeutigam
FZJ, Juelich, Germany

At present the ESS super-conducting option is under consideration, where the linear accelerator is divided into two main parts: the low energy part up to 100 MeV and the high energy super-conducting part from 100 MeV to 1333 MeV. The only change of frequency just after the funnelling allows to fill each separatrix in the accelerator, which results in the smaller number of particles in each bunch and makes easier to fulfil the particles losses requirements. Simultaneously the funneling helps to reach the required beam intensity for ESS of 107 mA in peak per micro pulse. Two identically bunched beams have to be merged into a single beam with double intensity. We propose the resonant method of the beams funnelling based on the multi-gap deflector working on mode. It is different from another method by the higher efficiency. We have analysed, designed and compared four types of different H-cavities, which would provide the effective resonant merging of beams. Additionally, instead of the pulse dividing method into two rings (or more for multi-purposes facilities) this device can be used to split the beam after acceleration into two or three beams and to deliver them to different facilities simultaneously. At present we make the real cavity to demonstrate this method.

Space Charge Compensation in High-Intensity Proton Rings

V.Shiltsev, et.al
FNAL, Beams Division

We propose to use negatively charged electron beams for compensation of space-charge effects in low-energy high-intensity proton rings. This presentation describes the idea and present results of recent R&D on the subject.

FFAG carbon synchrotron with high field permanent magnets

Masayuki Kumada and Yasuo Hirao
National Institute of Radiological Sciences

A spiral type FFAG synchrotron has a merit of using high field static magnet and its compactness. To achieve higher field stronger than that of conventional magnets, permanent magnets of more than 3 Tesla are designed and manufactured. Its test results and a conceptual design for FFAG synchrotron are reported.

Control of Coherent Instabilities by Linear Coupling

R. Cappi, E. Metral, D. M・l
CERN, Geneva, Switzerland

One of the main challenges involved in the design of high energy colliders is the very high luminosity necessary to provide significant event rates. This imposes strong constraints to achieve and preserve beams of high brightness, i.e. intensity to emittance ratio, all along the injector chain. Amongst the phenomena that can blow-up and even destroy the beam are transverse coherent instabilities. Two methods are widely used to damp these instabilities. The first one is Landau damping by non-linearities. The second consists in using an electronic feedback system. However, non-linearities are harmful to single- particle motion due to resonance phenomena, and powerful, wideband feedback systems are expensive. It is shown in this paper that linear coupling is a third method that can be used to damp transverse coherent instabilities. The theory of collective motion is outlined, including the coupling of instability rise/damping rates, chromaticity and Landau damping. Experimental results obtained at the CERN PS are reported, which are important for its role as LHC injector. Stabilization by coupling explains (at least in part) why existing high intensity accelerators and colliders work best when adjusted to be relatively close to a coupling resonance. This method could be profitably used in the design of new machines.

Positron-Production Experiment by 8-GeV Channeling Electrons in Crystal Tungsten at the KEKB Injector Linac

T.Suwada, S.Anami, A.Enomoto, K.Furukawa, K.Kakihara, T.Kamitani,Y.Ogawa, S.Ohsawa, T.Oogoe
Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
H.Okuno
Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
T.Fujita, K.Umemori, K.Yoshida
Hiroshima Synchrotron Radiation Center, Hiroshima University, 2-313 Kagamiyama, Higashi-Hiroshima 739-8526, Japan
R.Hamatsu, K.Sasahara
Department of Physics, Tokyo Metropolitan University, 1-1 Minami-Ohsawa, Hachioji-shi, Tokyo 192-0397, Japan
V.Ababiy , A.P.Potylitsin, I.E.Vnukov
Nuclear Physics Institute, Tomsk Polytechnic University, 634050, P.O.Box 25, Tomsk, Russia

An experiment to study the positron production efficiency by 8-GeV electrons hitting an axially-oriented tungsten monocrystalline target has been carried out by using single-bunch beams with a pulse width of 10 ps from the KEKB injector linac. Two kinds of targets are tested in this experiment: (1) a 2.2-mm-thick crystal tungsten, a combination of the crystal and an amorphous tungsten (5.0 and 10.0 mm thick). The experimental setup was constructed in front of a beam dump of the beam-energy-analyzer line in the linac end station. Positrons emitted from the target in the forward direction are momentum-analyzed by a magnetic spectrometer in the momentum range of 10-30 MeV/c and are detected with a 3-mm-thick acrylic Cherenkov counter and a lead-glass calorimeter. Since the produced positrons are also shortly bunched, the number of positrons per bunch are measured as a pulse charge from each detector. The positron yields have been measured for each target as a func! tion of rotational angles of a goniometer. For the 2.2-mm-thick crystal target, five-times enhancement of the positron yield have been observed when the crystal axis <111> is oriented to the incident electron beam. Also for the combined-type target, the positron yield enhancement up to about 90% is measured. This paper describes the first results of this series of experiments together with some simulation results which take into account the channeling radiation and coherent bremsstrahlung processes in crystal.

INTENSITY DOUBLER: A PROPOSAL FOR A MAJOR UPGRADE OF THE KEK 12GEV-PS

Ken Takayama, Dai Arakawa, Yoshio Arakida, Susumu Igarashi, Yoshiro Irie, Masahiko Uota, Tadamichi Kawakubo, Junichi Kishiro, Hikaru Sato, Yoshito Shimosaki, Masashi Shirakata, Takeshi Toyama, Eiji Nakamura, Katsumi Marutsuka, Isao Yamane
High Energy Accelerator Research Organization (KEK),Accelerator Laboratory
Koichiro Nishikawa and Makoto Sakuda
High Energy Accelerator Research Organization, Institute of Particle and Nuclear Studies
Masaharu Numajiri
High Energy Accelerator Research Organization, Applied Research Laboratory

A proposal for a major upgrade of the KEK 12GeV-PS is presented. The proposal involves a combination of beam stacking in a 500MeV accumulator ring (AR) and acceleration of a super-bunch in the 12GeV main ring (MR), referred to as the Intensity Doubler　(ID). A super-bunch is created in the AR by barrier-bucket stacking of 12 bunches injected from the booster ring (BR), and is transferred to the MR in one turn. By introducing the AR in the 12GeV-PS accelerator complex, it is possible to reduce the present injection time of about 500msec and increase the machine duty-cycle. Super-bunch acceleration is achieved by rapidly switching induction units. Through the final two years of the K2K experiment, the ID could supply proton beams that would be two times higher than the present levels in terms of averaged intensity. The scheme is based on the concept of induction synchrotron [1]. If the ID is realized, it would be the first demonstration of induction synchrotron. Quite unique features of super-bunch acceleration such as bunch-stacking in the barrier bucket or transition crossing avoiding tilt in the phase-space are reported with actual parameters of the KEK-PS. [1] K.Takayama and J.Kishiro, Induction Synchrotron, Nucl. Inst. Meth. A451/1, 304 (2000)

X-ray Free Electron Lasers based on the TESLA Linear Accelerator

J. Rossbach
Deutsches Elektronen-Synchrotron DESY Notkestrasse 85 D 22607 Hamburg

Superconducting linacs are considered the optimum accelerators to drive Free Electron Lasers at wavelengths in the Angstrom range. Thus, within the proposed TESLA project, a combined use of the superconducting linac is foreseen to accelerate beams for both high-energy e+/e- collisions and for driving an Angstrom FEL user facility. The paper summarizes the accelerator and FEL physics issues of the proposed TESLA FEL facility. Challenges and perspectives are discussed on the background of the present state-of-the-art FELs based on the Self-Amplified Spontaneous Emission principle.

PROGRESS IN CRYSTAL EXTRACTION AND COLLIMATION

Valery M. Biryukov
IHEP, Protvino (Russia)

Recent IHEP Protvino experiments show efficiencies of crystal-assisted slow extraction and collimation in the order of 70-80%, at the intensities of the channeled beam on the order of 1.e12. The obtained experimental data well follows the theory predictions. We compare the measurements against theory and outline the theoretical potential for further strong improvement in the efficiency of the technique. This success is important for the efficient use of IHEP accelerator and for implementation of crystal-assisted collimation at RHIC and slow extraction from AGS onto E952, now in preparation. Future applications, spanning in the energy from order of 1 GeV (scraping in SNS, slow extraction from COSY) to order of 1 TeV and beyond (scraping in Tevatron, LHC, VLHC), can benefit from these studies.

High Energy Laser-Plasma Accelerator Developments at JAERI-APR

H. Kotaki, T. Hosokai, S. Kanazawa, M. Kando, S. Kondo, H. Kotaki, T. Yokoyama (JAERI), H. Nakanishi, K. Nakajima(KEK)

Recently there has been tremendous world-wide progress on ultrahigh field particle acceleration deriven by ultraintense laser pulses in plasmas, demonstrating electron acceleration up to the order of 100 MeV with the accelerating gradient of the order of 100 GeV/m. The next step of laser-plasma accelerator developments has been focused on the injection of ultrashort electron bunches into a correct acceleration phase and on the optical guiding of ultraintense ultrashort laser pulses in underdense plasmas for the next generation high energy accelerator development. A proposal of laser-plasma accelerator developments has been presented to accomplish high energy gains of the order of GeV in a cm-scale length with high quality electron beam injection. The GeV laser acceleration research has been conducted at JAERI-APR using the 100TW, 20 femtosecond laser system and the high quality electron beam injectors consisting of the photocathode RF gun and the 150 MeV microtron. A femtosecond electron bunch injection with femtosecond synchronization will be generated by bunch slicing technique with the laser-electron beam interaction in an undulator, based on the inverse free electron laser acceleration mechanism. A GeV beam will be accelerated by 70 GeV/m laser wakefields generated in a 3 cm capillary plasma waveguide. The recent achievements of the laser acceleration research project at JAERI-APR is reported.

High- Energy Laser Ponderomotive Acceleration

Igor V. Smetanin
P.N. Lebedev Physics Institute & Accelerator laboratory, KEK
Christopher D. Barnes,
Stanford University
Kazuhisa Nakajima,
Accelerator Laboratory, KEK

Current progress in high-power femtosecond laser technique has renewed the interest in laser ponderomotive acceleration (LPA). Conventional LPA theories assume the vacuum laser-particle interaction, in which the group velocity of laser pulse is equal to the vacuum speed of light c, and result in the particle energy gain increasing with laser peak intensity. However, in real experimental schemes the gas jet is usually used as a target, and the group velocity has to be less than c. It leads to the natural limit in energy gain with an increase in peak intensity, when the particle acquire velocity close to that of the laser pulse. In this report, we propose a new regime of laser ponderomotive acceleration of particles, which is realized when the group velocity of high-power laser pulse is less than the vacuum speed of light. The physical mechanism of this regime is just the elastic scattering of the particle by the ponderomotive potential in the reference frame moving with the laser pulse. The regime proposed has a number of distinctive features, which make it quite different than conventional vacuum LPA. We show that in this regime, the energy gain is determined by the particle initial energy and pulse group velocity only, and does not depend on laser intensity. The maximum energy gain, 2(\gamma^2-1) for particle initially at rest, is for the direction of laser pulse propagation, \gamma is the Lorentz factor corresponding to the pulse group velocity. The energy gain and the acceleration process are insensitive to the phase of injection Laser intensity determines the probability for the particle to be reflected from the leading edge of the pulse, and, thus, the number of particles captured in the acceleration regime. To estimate it, we use the solution of Klein - Gordon equation. We show that the probability scales as ~ (a_0/\gamma)^4, a_0 is the laser peak normalized amplitude, when the particle energy in the moving frame is well above the potential barrier, and rapidly grows up to unity at energies below the barrier. Estimates show that the regime proposed is a promising technique for compact high energy laser acceleration. To get 1TeV electrons, the laser group velocity Lorentz factor should be \gamma ~ 10^3. At the laser pulse intensity ~10^21W/cm^2 and wavelength of ~1micron (i.e., normalized amplitude is ~30) we have the reflection probability ~10^{-6} which corresponds to ~10^3 particles at 10^19 cm^{-3} the plasma density in a focus of ~10 microns waist.

VERY LOW OUTPUT-IMPEDANCE RF SYSTEM FOR A PROTON SYNCHROTRON

Toshiyuki Oki, Yoshiro Irie and Susumu Takano
KEK

The very low output-impedance RF system is required for a high intensity proton synchrotron in order to cancel the beam loading. A grounded-cathode scheme, having dual resonant circuits, can provide such system. The one resonant circuit comprises a parallel tuned circuit between grid and ground, and the other a feedback loop between plate and grid. The model system has been tested using the Eimac 3CW40,000H3 triode as a final tube. By choosing the appropriate resonant frequencies, the output impedance is obtained as a few tenths of ohms and the voltage gain 6-10 over the frequency range of 2.5-8.5 MHz. Stability of the system is also discussed.

EVALUATION OF COPPER SURFACE FOR X-BAND ACCELERATOR STRUCTURES

Toshiyasu Higo, Kenji Saito, Yoshio Saito and Nobukazu Toge
KEK, Accelerator Research Laboratory
Yoshisato Funahashi, Nobuteru Hitomi, Yasuo Higashi, Toshikazu Takatomi and Yuichi Watanabe
KEK, Mechanical Engineering Center
Shinichi Kobayashi
Saitama University, Electrical and Electric Systems Engineering

It was found recently that 1-2m long X-band accelerator structures suffered from a severe frequency change during a few thousand hours operation at an accelerating field over 50MV/m. The frequency change comes from the erosion of copper surface around a high field region. We started analysing the copper surface equivalent to recent X-band structures and trying to find a cure to suppress the erosion. This microscopic approach complements the macroscopic approach where the electrical design of the structures is modified to suppress the breakdown damage. The surface characteristics are measured with using SEM etc. and the test pieces through various processes are compared with among themselves to study the direction of the possible cures.

Non-destructive Single Pass Monitor of Longitudinal Charge Distribution

P.A. BAK, N.S. DIKANSKY, E.A. GOUSEV, M.B. KORABELNIKOV, P.V. LOGATCHEV, S.V. SHIYANKOV, A.S. SIGANOV, A.A. STAROSTENKO, A.R. FROLOV
BINP, Novosibirsk, Russia

First experimental tests of a single pass non-destructive monitor of the linear charge density in an intense relativistic bunch have been held at the Budker INP in Novosibirsk. The method is based on the scanning of deflections of a thin, low current and continuous electron beam in the electromagnetic field of an intensive relativistic bunch. The data processing after such measurements results in the instantaneous linear charge distribution of the tested bunch. The probe beam-with particle energies within the range 20-100 kV-was injected in the vacuum chamber of the accelerator in the direction perpendicular to the motion of the tested intensive relativistic bunch. This type of an electron beam probe is suitable for both circular and linear accelerators with sort intense particle bunches.

Design and Test of a Fast Feedbacksystem for Orbit Correction at TTF and the TESLA Linear Collider

Klaus Balewski, Hans-Thomas Duhme and Jens Klute
DESY
D. Keese (DESY), C. Magne (Saclay), F. Obier (DESY), I. Reyzl (DESY), J. R・mler (DESY), M. Schroeder (DESY)

To achieve high luminosity in the TESLA Linear Collider feedback systems will be needed to provide orbit corrections within the bunch train. A prototype of the complete vertical feedback system has been installed in the TESLA Test Facility at DESY. The use of digital signal processing techniques led to a fast and highly flexible solution for the controller function. Additional features such as data logging and analysis allow to adjust the feedback parameters easily and to controll the performance of the whole system. An overview of the feedback will be presented as well as the results of first measurements.

Permanent Magnets for the 500 MeV Accumulator Ring of the Intensity Doubler Project in KEK-PS

E. Nakamura, K. Egawa, S. Igarashi and K. Takayama
High Energy Accelerator Research Organization (KEK), Accelerator Department
K. Ogata
Tokin Corporation

A 500 MeV accumulator ring (AR) is proposed as a part of the Intensity Doubler (ID) Project in KEK-PS. The AR will be installed in the same tunnel of the 12 GeV main ring. A total amount of 112 permanent magnets are required for the AR and beam transport lines from the booster ring and into the main ring; 88 gradient magnets, 12 quadrupoles, 8 bending magnets and 4 Lambertson magnets, with a wide mechanical aperture of a +/-50 mm transverse good field region and one or two meters long. The field is shaped by precision iron pole pieces. The temperature dependence of the ferrite is crucial to control the beam orbit in the actual tunnel environment with a variation of +/-3 degrees at least. The use of Ni(30%) Fe(70%) alloy operating near its Curie point is expected to compensate a gap field degradation due to the temperature variation. A prototype gradient permanent magnet one-meter long with a 70 mm center gap height is assembled to investigate its field per! formance and defects to be solved. The field is driven by strontium ferrite permanent magnets. In the conference, field measurement results will be presented and interested issues such as multipole components in field and a temperature compensation will be discussed.

Status of Beam-Beam Compensation with Electron Beams in Tevatron

V.Shiltsev, et.al
FNAL, Beams Division

We report recent progress in the compensation of beam-beam effects in the Tevatron collider with use of electron beams. The first "proof-of-principle" experiment should demonstrate the betatron tune shift of -0.01 by a single electron lens with electron beam radius 3 times larger than rms pbar beam size.

VEPP-4M OPERATION IN THE LOW-ENERGY RANGE

VEPP-4M Team
BINP, Novosibirsk

The possibility of effective operation of the modified e+e- collider VEPP-4M with the new detector KEDR in the low-energy range of 1-1.8 Gev is discussed. This energy range is unusual for the facility but it is of interest for measuring the total cross section of the e+e- annihilation into hadrons and studying the J/Psi physics. We plan to perform in the nearest future an experiment on the high precision measurement of the tau lepton mass in the vicinity of the threshold of its production (1.78 GeV) using the method of the resonance depolarization. Preliminary experimental data on the luminosity optimization at low energies are given and analyzed. The most important for VEPP-4M problems related with luminosity, such as the single-beam effect of vertical oscillations self-excitation depending on the beam current and length, the parasitic synchro-betatron resonances, stability and reproducibility of the operation regimes (residual fields and calibration errors), the variant of the betatron coupling localization at the KEDR section with a longitudinal magnetic field due to the use of two skew quads instead of compensating solenoids, the application of two dipole wiggler magnets of a 1.8 Tesla field for raising the peak luminosity due to the beam "blow-up" and increase in radiation damping decrements are under consideration.

Measurements of intra-beam scattering at low emittance in the Advanced Light Source

Dennis Atkinson, John Byrd, John N Corlett, Hiroshi Nishimura, David Robin, Stefano De Santis, Christoph Steier, Andrej Wolski, Ying Wu
Lawrence Berkeley National Laboratory
Scott Anderson, Karl Bane, Tor Raubenheimer, Marc Ross, John Sheppard, Tonee Smith
Stanford Linear Accelerator Laboratory

The beam emittance at the interaction point of linear colliders is expected to be strongly influenced by the emittance of the beams extracted from the damping rings. Intra-beam scattering (IBS) potentially limits the minimum emittance of low-energy storage rings, and this effect strongly influences the choice of energy of damping rings. Theoretical analysis suggests that the NLC damping rings will experience modest emittance growth at 1.98 GeV, however there is little experimental data of IBS effects for very low-emittance machines in the energy regime of interest. The Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory is a third-generation synchrotron light source operating with high-intensity, low-emittance beams at energies of approximately 1 - 2 GeV, and with emittance coupling capability of 1% or less. We present measurements of the beam growth in three dimensions as a function of current, for normalized natural horizontal emittance of approximately 3 - 10 mm-mrad at energies of 1 - 1.5 GeV, values comparable to the parameters in an NLC damping ring. Using a dedicated diagnostic beamline with an x-ray scintillator imaging system, measurements of the transverse beamsize are made, simultaneously with bunch length measurements using an optical streak camera. Emittance growth as a function of bunch current is determined, and compared with theoretical estimates. By varying parameters such as coupling, energy, RF voltage, and momentum compaction, we separate impedance driven effects from the IBS, and derive emittance growth from IBS alone.

Flip-flop Instability of Colliding Bunches with Round Cross Sections

D.V. Pestrikov
Budker Institute of Nuclear Physics, 630090 Novosibirsk, Russian Federation

Selfconsistent beam-beam interactions of colliding bunches can change their transverse sizes due to the so-called flip-flop instability. This instability may result in a proportional increase in the horizontal and vertical sizes of a bunch conserving its aspect ratio, or in an increase with the variation of the aspect ratios of colliding bunches. Within the framework of a simplified model calculating the so-called dynamic beta-functions at the interaction point, we discuss the flip-flop instability of colliding bunches with variations of the beam aspect ratios. These calculations show that, even for symmetrical unperturbed lattice conditions of colliding bunches, the flip-flop instabilities conserving the bunch aspect ratios and that changing the aspect ratios of colliding bunches occur within different and non-intersecting stopbands in the working plane of betatron tunes. In particular, this effect can limit the beam-beam performance of the colliding bunches with round cross sections.

Halo-formation and Equilibrium in High Intensity Hadron Rings: A Role of Nonlinear Parametric Resonances Excited by Intrinsic Beam-Core Oscillations

Yoshito Shimosaki
Kyushu University, Department of Applied Quantum Physics and Nuclear Engineering
Ken Takayama
KEK, Accelerator Laboratory

The emittance growth and halo formation for a beam of a 2-D Gaussian distribution in a realistic focusing channel were examined by means of macro-particle simulations [1] and the isolated nonlinear resonance theory. The nonlinear resonance driven by parametric interactions between a core oscillation and highly nonlinear motions of an individual particle has been proved to be a major cause responsible for emittance growth and halo-formation [2]. Halo has been identified as the outer edge of resonance islands. In addition, a speculation can be evaluated from the simulation results that the beam distribution arrives at an equilibrium state through some transient state after injection. According to the speculation [3], the injected particles are remarkably perturbed by the nonlinear resonance induced by mismatched core-oscillation and redistributed through the so-called nonlinear filamentation; eventually the phase-space structure is largely smeared out. Then, the! distribution is subject to the parametric nonlinear resonance induced by the intrinsic core-oscillation that is uniquely determined from the lattice. At last stage the distribution arrives at an equilibrium state. In the conference a whole story will be clearly demonstrated by the aid of computer simulations and a newly developed resonance theory. [1] Y. Shimosaki and K. Takayama, Proc. of EPAC, Vienna, Austria, 2000, p1330 [2] Y.Shimosaki and K.Takayama,Phys. Rev. E 62, 2797-2803 (2000). [3] Y.Shimosaki and K.Takayama, Phys. Rev. E, to be submitted.

Current Status of 1.2 GeV Booster Electron Synchrotron and Implementation for Nuclear Study at Tohoku University

H. Hama, F. Hinode, O. Konno, A. Kurihara, A. Miyamoto, M. Mutoh, M. Nanao, M. Oyamada, Y. Shibasaki, K. Shinto, S. Takahashi
Laboratory of Nuclear Scienece, Tohoku University 1-2-1 Mikamine, Taihaku-ku, Sendai 982-0826, Japan

A 1.2 GeV booster electron synchrotron with combined use of pulse-beam stretcher (STB ring) was commissioned and became routinely operational recently at LNS, Tohoku University. Energy ramping from the injection energy of 200 MeV to 1.2 GeV takes 1 s, and the flat-top duration is able to be arbitrarily extended, which means a beam storage mode is also available. At the present accelerated/stored beam has been utilized for study of nucleon resonance in nuclear matter by means of Bremsstrahlung photons produced from an internal target wire. The photon energy is tagged by a counter array mounted in a bending section where the magnet is used as an energy analyzer for scattered electrons. Because of finite energy range of the tagging counter, the booster has to be operated with various flat-top energies to shift the photon energy range. Deviation of the beam orbit depending on the flat-top beam energy is a critical issue to maintain an identical experimental condition. The betatron tunes at different flat-top energies should not be changed in order to keep same phase advances from sources of COD. Furthermore, because the target wire is located at a non-dispersion free section, the dispersion function should remain the same as well if the beam energy is deviated from the central energy. Prior those careful machine tuning, beam diagnostics is in progress. Currently achieved performance of the STB ring and latest progress will be reported.

Measurements of Slow Ground Motion for FNAL Future Colliders

V.Shiltsev, et.al
FNAL, Beams Division

Slow ground motion may significantly deteriorate operation of large colliders, including proposed future FNAL accelerators, Very Large Hadron Collider (VLHC) and NLC. We report results and conclusions of our 1.5 year long experimental studies of slow ground motion at FNAL and in deep Illinois dolomite mine. We aslo present plan of future studies.

Effect of the Space Charge Fields on Landau Damping of Dipole Transverse Coherent Oscillations

D.V. Pestrikov
Budker Institute of Nuclear Physics, 630090 Novosibirsk, Russian Federation

Without external non-linear fields the space charge fields of an intense beam do not affect its dipole transverse coherent oscillations. However, an interference of, for example, a cubic nonlinearity of the lattice focusing and of nonlinear space charge fields of such a beam changes the betatron tune distributions in the beam and hence, changes the Landau damping of its dipole coherent oscillations. For conventional coherent instabilities, which occur outside the lattice resonance stopbands, this interference changes the shape of the stability diagram of dipole coherent oscillations. This effect can be used to determine the Laslett tine shift of intense beam measuring the stability diagram of its dipole transverse coherent oscillations, or the response functions of these oscillations.

Characteristics of Russian Cryogenic Temperature Sensors under Magnetic Fields

Yuri A. Dedikov and Gennadi A. Kytin
National Scientific and Research Institute for Physical and Technical and Radiotechnical Measurements - VNIIFTRI, Mendeleyevo, Moscow Region, Russia
Yuri P. Filippov and Asiya K. Sukhanova
Joint Institute for Nuclear Research - JINR, Dubna, Moscow Region, Russia

The report presents the results of our activity during many years in the field of cryogenic thermometry and metrology applied to superconducting installations operating in the magnetic field - accelerators and detectors, in particular. Four types of Russian commercially available cryogenic resistive temperature sensors were investigated in the ranges from 1.5 K to 300 K and up to 10 T. They are platinum (PRT), rhodium-iron (RIRT), carbon-glass (CRT) and carbon TVO-resistors. The CRT and TVO sensors with negative temperature coefficient have shown minimal values of the temperature shift of several percent due to magneto-resistance, dR. An important advantage of both carbon sensors is that their readings practically do not depend on the orientation in the magnetic field. The expressions to calculate the temperature shift, dT, for them due to the magnetic field, B, are given. The magneto-resistance of the PRT and RIRT sensors with positive temperature coefficient is significantly larger than for CRT and TVO at low temperatures. However, the way to determine the values of dT(B, T) for RIRT and PRT with the accuracy of 0.02 K or better is possible even for low temperatures. Two approaches to calculatedT(B, T) are described: individual calibration in the magnetic field and approximate method. The first one provides the accuracy about 0.01 K for dT(B, T). The second method is based on the average experimental data dR/R(B, T) obtained for several temperature sensors of each type, and it allows one to find the value of dT(B, T) with the accuracy better than 0.03 K. The corresponding equations are valid for RIRT sensors in the ranges (3 - 80) K and (0 - 7) T. The behavior of PRT sensors in the magnetic field can be described by another expression: the deviations of the dT-values from the experimental points do not exceed 0.02 K for the ranges (30 - 190) K and (0 - 7) T. The influence of orientation of the PRT and of the RIRT sensors in the magnetic field is described as well. The corresponding equations for TVO and CRT sensors are valid for (1.5 - 4.2) K and up to 10 T, and (2 - 80) K & (2 - 8) T, correspondingly.

EXPERIMENTAL VERIFICATION OF SELF-AMPLIFIED SPONTANEOUS EMISSION IN THE FAR-INFRARED REGION

R. Kato, R. A. V. Kumar, T. Igo, M. Kuwahara, T. Konishi, M. Fujimoto, Y. Nakamura, S. Isaka, S. Mitani, S. Okuda, S. Suemine and G. Isoyama
Institute of Scientific and Industrial Research, Osaka University

We have been conducting experiments to generate Self-Amplified Spontaneous Emission (SASE) in the far-infrared region and to measure its characteristics, using the high intensity single bunch beam accelerated with the L-band linac at the Institute of Scientific and Industrial Research (ISIR), Osaka University. High-intensity infrared-light was observed when the single-bunch electron beam with a peak current higher than 1 kA passed through a 32-period planar wiggler with the period length of 6 cm and that it was concluded to be due SASE, judging from the intensity variation with the K-value of the wiggler. We have measured wavelength spectra of SASE in the far-infrared region. SASE emitted in the wiggler by the single bunch beam of 12 MeV energy was guided through an evacuated optical transport line to the measurement room, and then measured in the wavelength region between 100 and 200 um using a grating monochromator and a liquid-He-cooled Ge:Ga detector. Some of the measured spectra show a few broad peaks. We are checking reproducibility of the experiments and analyzing the measured data. We will report results of these experiments and analysis.

Design of Dipole Magnet for the 3-GeV Proton Synchrotron of the JAERI/KEK Joint Project

Norio Tani, Taihei Shimada, Fengqing Zhang, Hiromitu Suzuki and Hideaki Yokomizo
Japan Atomic Energy Research Institute (JAERI), Accelerator Group
Toshikazu Adachi and Yoshiro Irie
High Energy Accelerator Research Organization (KEK), Accelerator

The 3-GeV synchrotron proposed in the JAERI/KEK Joint Project [1] is a rapid-cycling synchrotron (RCS), which accelerates a high-intensity proton beam from 400-MeV to 3-GeV at a repetition rate of 25-Hz. The 3-GeV synchrotron is used to produce pulsed spallation neutrons and muons. It also works as an injector for a 50-GeV synchrotron. The magnets for the 3-GeV synchrotron are required to have a large aperture in order to realize the large beam power of 1-MW. There are many problems in a rapid-cycling magnet with the large aperture. Therefore, a prototype dipole magnet has been constructed and investigated. This paper reports the result of the preliminary test about the prototype dipole magnet.
[1] Y. Yamazaki, Y. Mori, M. Mizumoto, H, Yokomizo, “High-Intensity Proton Accelerators for the JAERI/KEK Joint Project”, EPAC 2000.

High pulse and average power low-induction load

Boris I. Grishanov and Fedor V. Podgorny
Lab. 5-0 of BINP, Novosibirsk

A high pulse and average power low-induction load with a built-in divider is described in this report. The load has a nominal resistance of 25 Ohm and is designed to operate with a repetition rate of up to 50 Hz at a pulse duration (FWHM) of 100 ns, a rise/fall time of 50 ns and a pulse amplitude of up to 50 kV. In this mode the dissipated energy is equal to about 10 J per pulse and average power is up to 500 W. At such a short pulse mode there is practically no heat removing from the load resistant layer during one pulse. Therefore the absorbing resistor should have large heat capacity of the conducting layer. To fit this condition the resistor is realized as a package of resistive rings connected in series, a number of insulating spacers and two terminal connectors. This construction is placed in a cylindrical insulating tube connected to a water-cooling system. The design of the load provides for a radial pumping of a coolant between conducting rings. The resistant element has external diameter of 50 mm and a length of 250 mm. The resistor can be used as an absorbing load and as a block element in high-voltage engineering.

A High Efficiency Long Pulse Multi Beam Klystron for the TESLA Linear Collider

A. Beunas, G. Faillon
Thomson TTE, France
S. Choroba, A. Gamp
DESY, Germany

The Tesla linear collider requires 600 pieces of 10MW L-Band klystrons operating at a pulse duration of 1.5ms and a repetition rate of up to 10Hz with an efficiency in the order of 70%. Since these performances are not achievable with a single beam klystron, a multi beam klystron (MBK), which uses many low perveance electron beams in parallel in one vacuum envelope, was developed by THOMSON TUBES ELECTRONIQUES (TTE). The advantage of this solution is the low voltage required and the high efficiency compared with a single beam klystron. THOMSON TTE has developed and manufactured the TH1801. This MBK is in operation at the Tesla Test Facility at DESY, where it was tested at full pulse duration of 1.5ms. It reached 10MW at 117kV and 131A with an efficiency of 65%. This paper reports on the tubes, the test results and the operation experience of the TH1801 multi beam klystrons built until now.

A NEW PROJECT IN LEBRA AT NIHON UNIVERSITY

I.SATO, I.KAWAKAMI, K.SATO, Y.MATSUBARA, K.HAYAKAWA, T.TANAKA, Y.HAYAKAWA, Y.NAKAZAWA, K.YOKOYAMA, K.KANNO, T.SAKAI, K.ISHIWATA, Y.NAKAMURA, H.INOKAWA
Laboratory for Electron Beam Research and Application in Atomic Energy Research Institute of Nihon University Narashinodai 7-24-1,Funabashi-chi, Chiba-ken ,274-8501 Japan

In Laboratory for Electron Beam Research and Application (LEBRA), a study for a variable wavelength source of directional X-ray has been continued several years before. Monochromatic and directive X-rays are emitted from a crystal irradiated by electron beam with high energy. This brilliant source is expected to have a fine performance by high-energy linac for FEL with excellence in quality. The study was promoted to put the source to practical use and was proposed as a new project for five years plan in December of 1999. The project makes full use of the 125 MeV linac for FEL and is in order to advancing interdisciplinary researches covered with physics, chemistry, biology, engineering and medical science. The project was also programmed to construct such equipment as a parametric X-ray source, beam lines of FEL, experimental devices for X-ray powder diffraction and protein structure analysis. The government at the fiscal year 2000 authorized the construction budget including a new experiment building. The project has been in progress by a collaboration of the whole college in Nihon University, other colleges and laboratories. The building and the main equipment for application research are under construction and intend to complete by the end of this fiscal year.

On the Modernization of SP-94 Magnet for np Experiment at LHE JINR with Polarized Neutron Beam of Multi-GeV Energies

I.P.Yudin, S.A.Dolgiy, E.P.Zhidkov, I.V.Zaitsev, E.A.Matyushevsky, G.P.Nikolaevsky, A.A.Nomofilov, R.V.Polyakova, V.Yu.Prytkov, A.Yu.Starikov, L.N.Strunov, V.I.Sharov, T.V.Shavrina
Joint Institute Of Nuclear Research, Dubna

By upgrading the iron yoke the deflecting power of SP-94 magnet is increased. One of the possible variants of mathematical model for SP-94 magnet in DELTA-SIGMA experiment at LHE JINR, is proposed By means of calculations the detailed map of the magnet's field was obtained. The problem of achieving uniform field in maximal part of the magnet's aperture via applicable ferromagnetic bars, was considered. The result of magnet field measurement was given for some reper points of the aperture.

CALCULATIONS OF THE SPACE-CHARGED BEAM OPTICS BY THE GREEN' FUNCTION METHOD

I.P. Yudin, V.V. Andreev
Joint Institute For Nuclear Research, Dubna 141980, Moscow Region, Russia

We describe the procedure within the transfer matrix formalism to obtain the solution of nonlinear equations of charge particle motion with space charge by the Green' function method.

A second feasibility study of a muon storage ring neutrino source

Robert B Palmer and Satoshi Ozaki
Brookhaven National Lab
Michael Zisman
Laurence Berkeley National Lab

This second feasibility study of a muon storage ring neutrino source was sponsored by the director of Brookhaven Lab. It was undertaken by the Muon Collider Collaboration with contributions from members from many institutions. The study had three components: 1) Simulations of a generic conceptual design; 2) Engineering and comparative cost determinations; and 3) Brookhaven Lab site specific considerations. The study differed from the first feasibility study, sponsored by the Fermilab director in 1999, in being for a lower energy (20 GeV instead of 50 GeV), higher intensity (by the use of liquid metal targets and other advances), and in the details specific to the use of an upgraded AGS as proton driver, and its location at BNL.

Technical and Physics Issues for Future HE Accelerators

Eric R. Colby
Stanford Linear Accelerator Center

The construction of a 5 TeV electron-positron collider poses a Herculean challenge, both technically and economically. With modern RF techniques the accelerating sections alone would stretch more than 100 km for each of the electron and positron linacs. Clearly, advances in accelerating gradient must be made if such a machine is to be affordable and reliable. Research on exploring improvements to existing microwave accelerators and exploring new acceleration concepts is therefore of critical importance to the future of accelerator-based high energy physics. The physical acceleration mechanism and significant technical challenges of high frequency (10 GHz to 400 THz) acceleration by coherent radiation coupling in metallic, plasma, and dielectric structures will be discussed in brief together with recent experimental results. Emphasis will be on key technical issues which must be resolved before each of these acceleration methods can become viable candidates for a collider.

Luminosity Limitations at Hadron Colliders

Frank Zimmermann
CERN, SL Division

I discuss fundamental luminosity limitations at hadron colliders, addressing beam-beam interaction, crossing angle, bunch length, intrabeam scattering, dynamic aperture, heat load, luminosity lifetime, synchrotron radiation damping, and the option of flat-beam collisions. Parameters of operating or past colliders - the Tevatron, RHIC, and the CERN SPS -, are compared with those of the LHC and then further extrapolated to a VLHC and an LHC upgrade.

Longitudinal phase space disruption in bunch compressors

Philippe Piot and Torsten Limberg
Deutches Elektronen Synchrotron-DESY HAMBURG GERMANY

It is now well-established that high-charge (nC-level) ultra-short (ps-level) bunches, such as the one required in the foreseen next generation of linear collider, can self-interact via radiative fields as they undergo curved trajectories, e.g. in magnetic bunch compressors. The two main consequences of this self-interaction is (1) an energy redistribution within the bunch, (2) a potential transverse emittance dilution in the bending plane. In this paper after briefly discussing some theoretical aspects of the phenomenon, we report on recent experimental results obtained at the Tesla Test Facility and compare them with numerical simulations using the program TraFiC4 [1]. [1] M. Dohlus, A. Kabel, T. Limberg, Nucl. Intr. Meth. A 445, pp. 338-342 (2000)

PLASMA ACCELERATORS CHARACTERIZED BY RF LINAC TERMINOLOGY

Atsushi Ogata
AdSM, Hiroshima University

Plasma accelerators are described by using RF linac terminology such as shunt impedance, filling time, transit time factor, quality factor etc.. It is shown that the beatwave accelerator has more similarity to RF linacs than wakefield accelerators, because it is regarded as a driven oscillator system. In the wakefield acceleators driven by single beams or single laser pulses, the shunt impedance is of limited use and the filling time is no use. The factors which deteriorate the quality factor in these acceleraotrs are discussed.

Laser Acceleration: status and outlook

W. P. Leemans
Lawrence Berkeley National Laboratory

Acceleration of particles with high power lasers using plasmas will be discussed. With the advent of high peak power ultra-short pulse laser systems, significant progress has been made on demonstrating the generation of multi-GV electric field gradients in plasmas and the trapping and acceleration of electrons in these fields to multi-MeV energies (> 100 MeV). By tightly focusing (5 - 10 micron) high power laser beams (multi-TW) into high density plasmas (> 10^19 cm^-3), high amounts of electrons per bunch (> 5 nC) have been accelerated in distances typically on the order of a mm, with beam divergence angles on the order of 10 mrad. However, due to the inherent lack of control in the present regime of laser wakefield acceleration experiments, beams with 100 % energy spread are produced. Despite this large "longitudinal" emittance, using high repetition rate lasers (10 Hz), nuclear activation experiments have been performed with gaseous targets, demonstrating that sufficiently high fluxes of high energy electron beams can now be produced. As a means of reducing the energy spread, experiments are underway on laser triggered electron trapping in the plasma waves through optical manipulation of plasma electrons by additional laser beams. To increase the net beam energy gain, development of optical guiding structures is being pursued to extend the acceleration distance from mm to cm. An overview of progress and challenges will be presented towards the controlled acceleration of electrons Recent results on laser driven proton acceleration will also be discussed.

Luminosity Limitations in e+/e- Linear Colliders

Tor O. Raubenheimer
Stanford Linear Accelerator Center

Electron-positron linear colliders provide a route to high energy lepton collisions. However, to attain the desired luminosity in such a facility requires colliding high power beams with very small spot sizes. In this paper, we will review the beam dynamics as well as the technical limitations that determine the luminosity in electron-positron linear colliders. We will discuss the situation for the current generation of colliders with center-of-mass energies around 500 GeV as well as future generations with much higher and possibly much lower center-of-mass energies.

Very Large Hadron Collider Studies

J. Strait
Fermilab, for the VLHC collaboration

Hadron colliders are the means by which particle physics expands the energy frontier. Studies and R&D are under way at many laboratories to develop accelerator designs and technologies that will be necessary to allow the construction of hadron colliders with greater reach than the Tevatron and the LHC. As an example that illustrates the range of accelerator physics and technology issues being studied, we will present a concept that uses first low-field and later high-field magnets in the same large-circumference tunnel. Such an approach spreads out the cost while providing unique opportunities at each stage for frontier high-energy physics, and an ultimate energy that cannot be reached by any other accelerator. The magnets and their programs under way to develop them will be discussed, along with the effects of synchrotron radiation, ground motion and other accelerator physics issues. Design concepts and preliminary specifications will be presented for both the initial low-field and ultimate high-field stages.

OBSERVATION OF COHERENT SYNCHRO-BETATRON BEAM-BEAM MODES AT VEPP-2M

I.N. Nesterenko, E.A. Perevedentsev and A.A. Valishev
Budker Institute of Nuclear Physics, Novosibirsk, 630090, Russia

An experimental evidence is presented of the coherent synchro-betatron beam-beam modes in the spectrum of coherent dipole oscillations observed at the VEPP-2M collider. The measured current-dependent behavior of the mode spectrum is in good agreement with predictions of our theoretical models, taking full account of the finite length of colliding bunches. Potential effect of the synchro-betatron modes on the beam-beam blowup is discussed.

STATIC SYNCHRO-BETATRON BEAM-BEAM EFFECT CAUSED BY CROSSING ANGLE

E.A. Perevedentsev
Institute of Nuclear Physics, Novosibirsk, 630090, Russia

Beam-beam collision with a crossing angle results in a static head-tail deformation of colliding bunches, proportional to the crossing angle and dependent on the bunch length, synchrotron and betatron tunes, and the beam-beam parameter. Because of residual x-y coupling at the interaction point, this deformation is not confined to the crossing plane. Nonlinearity of the beam-beam kick leads to enhancement of the effective emittances in the both transverse planes, which is detrimental to the luminosity, especially for flat colliding beams. The static head-tail deformation effect is strongly reduced by setting the collider working point well apart from the integer resonances, which in practice means that both betatron tunes should be slightly above a half-integer, and reasonably far from the main coupling resonance.

Plasma Focusing of High Energy Density Electron and Positron Beams

Johnny S.T. Ng
Stanford Linear Accelerator Center, Accelerator Research Department A

The plasma lens was proposed as a final focusing mechanism to achieve high luminosity for future high energy linear colliders. Previous experiments to test this concept were carried out with low energy density electron beams. In this talk, we present results from the SLAC E-150 experiment on plasma focusing of 29 GeV electron and, for the first time, positron beams. The experiment was carried out at the SLAC Final Focus Test Beam facility, with 1.5x10**10 particles per bunch, bunch length of 0.7 mm, and beam cross-section of 7 microns by 3 microns. The plasma lens was created from beam-induced as well as laser-induced ionization of a pulsed neutral gas jet. The synchrotron radiation induced by the strong bending of the beam particles inside the plasma lens was observed for the first time. The effective critical energy was determined to be approximately 5 MeV, corresponding to a bending field strength of 1 Mega-Tesla / m. Results on laser- and beam-plasma interactions are also presented.

Enhanced radiative ion cooling

Evgueni G. Bessonov
Lebedev Physical Institute RAS, High Energy Physics Department

A two-dimensional scheme for enhanced laser cooling of both nonfully stripped (atomic transitions) and fully stripped (nuclear transitions) ions is discussed. Coupling of horizontal and vertical betatron oscillations leads to a three-dimensional ion cooling [1].

Heavy Ion Colliders - The Next Generation

Fulvia Pilat
Brookhaven National Laboratory

High luminosity will extend the physics reach of Heavy Ion Colliders beyond the present quark-gluon plasma (QGP) production capabilities, into the domain of hard scattering quarks and gluons in a QGP, and into the detection of rare processes. After a review of the physics potential of Heavy Ion Colliders, the luminosity limitations of such machines will be discussed, with particular emphasis on the intra beam scattering (IBS) mechanism. Plans are being developed for a staged luminosity upgrade of RHIC: initially, the luminosity will be optimized by increasing focusing and number of bunches, but a luminosity increase of over a factor ten will require higher bunch intensities and lower emittances, the latter only achievable by electron cooling of the RHIC beams at top energy. Electron cooling at RHIC is feasible and a design for the electron beam based on a recirculation linac already exists. The Heavy Ion option of the LHC is also actively studied and planned at CERN, with the goal of a high energy Heavy Ion Collider coming on line in the second half of this decade. Challenges and features of this machine, including luminosity optimization, and recent developments, are reviewed and discussed.

Muon Colliders: Conception and Some Distinguished Features of Physics Potential

Feodor F. Tikhonin
Institute for high Energy Physics Protvino, Moscow region, RUSSIA

Recently, the possibility of building $\mu^+\mu^-$ colliders has received considerable attention. At these machines, unlike an electron-positron collider, the process of resonant Higgs boson production is possible. However the idea of "Higgs factory", unfortunately, fails, if the value of Higgs boson mass $m_H \geq 2m_W$. Under these circumstances the process $\mu^+ \mu^- \, \to \, \gamma H^0$ would be grately helpful. It receives tree level contributions on an equal foot with the one-loop contributions (with heavy particles in loops). Both contributions are of comparable magnitude, but former dominates at the c.m. energies $ m_H < \sqrt{s} < 2m_H $ while latter dominates in the region where $\sqrt{s} > 2m_H$. So, the unique possibility appears for probing anomalous Higgs couplings through the sole process $\mu^+ \mu^- \, \to \, \gamma H^0$ with leptons and, for example, with t-quarks Also, QED corrections to the process considered have been calculated at the one - loop level and in the Leading Logarithm Approximation. Calculations show, that the cross-section is drastically affected by both types of radiative corrections in the vicinity of "dangerous" point $ \sqrt{s} \simeq m_H $ only. Away this point radiatevly corrected cross-section differs from that of tree level by percentage only. Also related process $f^+ f^- \, \to \, Z^0 H^0$ (f - fermion) is discussed briefly. For the case of finite initial masses it exhibits the most deep and fine properties of Electroweak Theory, concerning high energy behaviour of tree amplitudes (saving the unitarity condition). Only two examples considered show, that the Muon colliders will deliver an excellent opportunity for the particle physics investigations.

WAVEGUIDE LASER WAKEFIELD ACCELERATION

Konstantin V. Lotov
Budker Institute of Nuclear Physics

The recently proposed scheme of laser pulse guiding in a narrow plasma-filled solid waveguide is discussed. The advantage of this wakefield acceleration scheme is that it enables to suppress the driver diffraction and control the driver trajectory perfectly. The wakefield wavelength in this case is determined by the density of the inner plasma and can be made large enough to provide effective wave generation. Parameters of the waveguide which provide the maximum energy gain of accelerated particles at given length and peak power of the driver are analyzed in the approximation of relativistically weak drivers. PIC simulations confirm that the wakefields inside the waveguide are regular and acceptable for acceleration even in a strongly nonlinear regime.

PROPOSAL ABOUT HIGH-CURRENT POLARIZED ELECTRON SOURCE WITH LONG LIFETIME ON THE BASE OF SECONDARY-EMISSION MAGNETRON INJECTION GUN

Sergiy.A. Cherenshchykov
Kharkiv Institute of Physics and Technology

Many years ago polarized electrons from the secondary emission were obtained from different materials by several authors. The secondary emission magnetron injection gun is a high current (the current up to 200 A and more) and durable (the lifetime is more than 100,000 hours) electron source with the cold (the temperature varies from 0 K to the melting point) cathode. The gun is novel universal electron source for charged particle accelerators. This gun is based on an unconventional principle. The principle consists in the self-sustained secondary emission multiplication in crossed fields. It can be expected that the beam from the secondary emission injection magnetron gun may be polarized. The possibility of creation polarized electron source on the similar principle is discussed. The main expected advantage is unlimited lifetime times at ordinary vacuum in high current (up to any hundred amperes) pulse mode. Expected level of polarization is up to 50% or more over.

TECHNICAL IMPLEMENTATION OF THE FEASIBILITY STUDY-II DESIGN

Michael S. Zisman
Center for Beam Physics Accelerator & Fusion Research Division Lawrence Berkeley National Laboratory

An updated Feasibility Study of a high-performance Neutrino Factory has been undertaken by BNL and the Neutrino Factory and Muon Collider Collaboration (MC). In this paper we describe the technical implementation of the facility described in the paper by R. Palmer (WE-02). The target system comprises a mercury-jet target immersed in a 20-T magnetic field provided by a superconducting solenoid having a hollow-conductor magnet insert. The 20-T field is smoothly reduced to 1.25 T over the next 18 m. Phase rotation is accomplished by a series of induction linac modules having superconducting solenoid focusing. Following the phase rotation, the beam is bunched at 201 MHz with a buncher section containing both 201- and 402-MHz cavities. After bunching, the beam enters a cooling channel having 201 MHz RF cavities with Be windows interspersed with liquid-hydrogen absorbers. At the end of the cooling channel, the beam is optically matched into a superconducting linac, with solenoidal focusing, that increases the beam energy to about 2 GeV, followed by a 4-turn recirculating linear accelerator that brings the beam to 20 GeV. To produce the neutrino beam, the 20 GeV muons are stored in a racetrack shaped storage ring, with one straight section oriented toward a detector some 3000 km distant from the ring. Details of the various proposed components will be described, along with an indication of R&D activities that need to be addressed to proceed with a facility design.

HIGH-RESOLUTION GRADIENT MAGNETOMETER

I. Bolshakova, R. Holyaka
Magnetic Sensor Laboratory, Lviv Polytechnic National University
M. Kumada
National Institute of Radiological Sciences

The present work is devoted to one of essential problems of modern magnetometry measurement of magnetic field distribution in space-limited objects, foremost in small gaps of strong magnets. Distinctive features of this problem is minimal dimensions of operating gaps of the magnets (units of millimeters), considerable values of magnetic fields (up to 4 T), non-uniform magnetic field with complex form of its distribution (for instance, caused by special constructions of magnet concentrator and yoke), strict requirements to the resolution and flexibility of measurement instruments etc. Taking into account that each specific problem like this one has also the whole number of its own features, the problem of field mapping in small gaps of magnets could be solved within the scope of separate R&D projects only.