Akai, K

Akemoto, M

Akiyama, H

Araki, S

Hayano, H

Higo, T

Ishihara, N

Kawamoto, T

Kimura, Y

Kobayashi, H

Kubo, T

Kuroda, S

Kurokawa, S

Matsumoto, H

Mizuno, H

Naito, T

Odagiri, J

Otake, Y

Sakai, H

Shidara, T

Shintake, T

Suetake, M

Takashima, T

Takata, K

Takeda, S

Takeuchi, Y

Urakawa, J

Yamamoto, N

Yamaoka, Y

Yokoya, K

Yoshida, M

Yoshioka, M

CERN Document Server

Particle Accelerators, 1990, Vol. 30, pp. 153-159Reprints available directly from the publisherPhotocopying permitted by license only© 1990 Gordon and Breach, Science Publishers, Inc.Printed in the United States of AmericaELECTRON LINAC OF TEST ACCELERATOR FACILITYFOR LINEAR COLLIDERSEISHI TAKEDA, KAZUNORI AKAI, MITSUO AKEMOTO,HIROSHI AKIYAMA, SAKAE ARAKI, HITOSHI HAYANO, TOSHIYASU HIGO,NOBUHIRO ISHIHARA, TAKASHI KAWAMOTO, YOSHITAKA KIMURA,HITOSHI KOBAYASHI, TOMIO KUBO, SHIGERU KURODA,SHINICHI KUROKAWA, HIROSHI MATSUMOTO, HAJIME MIZUNO,TAKASHI NAITO, JYUNICHI ODAGlRI, YUJI OTAKE,HIROSHI SAKAI, TETSUO SHIDARA, TSUMORU SHINTAKE,MASAAKI SUETAKE, TAKEO TAKASHIMA, KOJI TAKATA,YASUKI TAKEUCHI, JYUNJI URAKAWA, NOBORU YAMAMOTO,KAORU YOKOYA, MASATO YOSHIDA, MASAKAZU YOSHIOKA,and YOSHlKAZU YAMAOKA·National Laboratory for High Energy Physics, Tsukuba, Ibaraki 305, Japan*The University of Tsukuba, Tennodai, Tsukuba, Ibaraki 305, JapanAbstract KEK has proposed to build a Test Accelerator Facility (TAF)capable of producing a 2.5 GeV electron beam for the purpose of stimulatingR&D for the JLC (Japan Linear Collider) project. The TAF consists of a 1.54GeV S-band linac, 1.54 GeV damping ring and 1.0 GeV X-band linac. The TAFproject will be carried forward in three phases. Through phase-I and phase-II, the S-band and X-band linacs will be constructed, and the damping ringwill be completed in phase-III. The construction of TAF phase-I has beenstarted, and a 0.3 GeV S-band linac has been almost completed.INTRODUCTIONAs a post-TRISTAN project, KEK has proposed a new project to pursue theenergy frontier physics by using an electron-positron colliding machine. 1-2) Itpresently be considered that the Japan Linear Collider (JLC) project should be startedat the center-of-mass energy around 400 GeV, which seems to be the optimum inorder to start experiment till the end of this century.3-4) At the first stage of JLCproject, the JILC (Japan Intennediate Energy Linear Collider) will be constructed at400 GeV center-of-mass energy, which is two times higher than that of LEP-II. Theenergy can be increased up to 600 GeV by extending the rf power system. At the finalstage of the JLC project, a 1 TeV linear collider will be constructed by extending thetotal length of the linacs.Table 1 shows the design parameters of 400 GeV JILC. It should be noted thatthese parameters are tentatively obtained. The parameters will be changed by thedetailed design studies carried out for each major sub-system, for example the main[1111]/153154/[1112] S. TAKEDA ET AL.linacs, damping rings and final focus systems. The JILC is installed in the straighttunnel with the total length of 10 kIn, which is required to increase the energy up to600 GeV. The multi-bunches of electrons are generated by an rf-gun and they areaccelerated up to 1.54 GeV by an S-band injector linac for a damping ring. Thedamping ring contains 8 bunch trains of 10 bunches each. One bunch train is kickedout every shot, after reducing the beam emittance. The bunches from the dampingring are compressed by the first bunch compressor from 4.5 rom to 350 J.1m. Thebunches are re-accelerated by an S-band preacceleration linac up to 10 GeV and theyare re-compressed to 60 J.1m by the second bunch compressor. The bunches areaccelerated by an X-band main linac up to 200 GeV. The electron and positronbunches are focused by the final focus system and they are collided at the interactionpoint.Table 1. Design parameters of 400 GeV JILCBeam energyLuminosityTotal length of the linacsNumber of particles/bunchRepetition frequency of linacsNumber of bunches/rf pulseNumber of bunches /secRm.s beam size at IPHorizontalVerticalAspect ratioR.m.s. bunch lengthDisruption parameterPinch enhancement factorEL*O'x*O'y * *R= O'x layO'zDx/DyHD200+200GeV3.1 x 1033 cm-2sec-110 kIn1.0 x 1010200Hz10 bunches2000 bunches/sec290nm2.2nm13260 J.1IIl0.103/13.51.5TEST ACCELERATOR FACILITY (TAF)The follOWing theoretical and technical R&D programs have been in progress bythe study group:4) design of linacs and damping rings,5, 14) beam dynamics in linacsand damping rings, studies on the interaction region, such as beam-beaminteractions,6-7) design of final focus system,8-9) high power rf sources to generatehigh accelerating gradients,10-12) accelerating structures capable of producing highgradient of 100 MeV/m,13) beam monitors, controls ,15-16) alignments, 17) intenseelectron and positron sources.As for the linear collider, the beam should stably be accelerated so as to collidethe sub-micron beams at the interaction point. Therefore, the R&D for the stabilityof both the linacs and the damping rings is highly required. The study group hasdecided to construct a test facility as a major R&D program. The proposed TestAccelerator Facility (TAF) consists of a 1.54 GeV S-band linac, 1.54 GeV.dampingring and 1.0 GeV X-band linear accelerator. Therefore the major part of the JILC canbe tested by using the test facility. The S-band linac is an injector of the dampingring, and a high current single bunch and multi-bunches are accelerated up to 1.54ELECTRON LINAC OF TAF FOR LINEAR COLLIDER [1113]/155GeV. The low emittance beam from the ring is compressed by the bunch compressorand it is re-accelerated by the high gradient X-band linac up to 2.5 GeV.The beamfrom the X-band linac will be utilized to test a prototype final focus system.The TAF project will be progressed through three phases. The S-band and X-band linacs will be constructed through phase-I and phase-II, and the damping ringwill be completed in phase-III. Table 2 shows the parameters of the linacs of the TAF.The 0.3 GeV S-band linac is under construction at the TRISTAN Nikko experimentalhall. A new building with an accelerator tunnel has been proposed in order to installlinacs.Table 2. Design parameters of the linacs ofTAFLinacPhaseEb(GeV)Ea(MeV/m)frtlGHz)Prj{MW/structure)Nk(Klystrons)Ns(structures)Ls(m/structure)Ne(electrons/bunch)Single bunchMulti-bunchesS-bandI0.340-502.8562004235x 10101 x 1010II1.5440-502.856200241235x 10101 x 1010X-bamII1.070 - 10011.4245010200.55 x 10101 x 10101.54 GeV 8-BAND INJECTOR LINACThe JILC is composed of the follOWing S-band linacs: two damping ring injectorsof 1.54 GeV each, two pre-accelerating linacs of 10 GeV each, and a 10 - 30 GeV linacfor positron generation. The R&D for the high gradient linacs in S-band frequency isalso required.The JILC is designed to collide the bunches at the repetition rates of 2000 pps.The linacs are operated at 200 Hz and 10 bunches are accelerated per shot. The bunchseparation in a bunch train is chosen as 16 buckets of 11.424 GHz, since the longerbunch separation suppresses the multi-bunch instability. An rf-gun with aphotocathode is a low emittance and high current source, since the emitted electronsare accelerated by high accelerating fields generated in the cavity. The pulsestructure of the emitted beam is detennined by the fine structure pulses of the mode-locked laser. The rf-gun makes it possible to generate multi-bunches with longerbunch separation, since the bunch separation can be tunable by adjusting the mirrorsystem of the laser. The lasertron is a DC-gun with a photocathode and mode-lockedlaser. The large portion of the basic techniques established by the lasertronproJect18) in KEK can be applied to the rf-gun. The rf-gun generates 10 bunches withthe bunch separation of 4 buckets of 2.856 GHz. The number of electrons in a bunch is1 x 1010 for the multi-bunches.The structures of the linac consists of 3 m-Iong constant gradient structures of21C/3 mode. In order to produce the gradient of 40 - 50 MeV/m in a 3 m-Iong structure,the rf power of 200 MW should be. required. The rf power from a pair of two SIAC-156/[1114] S. TAKEDA ET AL.5045 klystrons are combined by a 3db coupler and the rf power of 200 MW, 1 J.1S can beobtained. Table 3 shows the parameters of the 1.54 GeV S-band injector linac.Table 3. Design parameters of 1.54 GeV injector linacBeam final energyRF frequencyAccelerating gradientBunch spacingNumber of bunchesNormalized emittanceRm.s. bunch lengthAccelerating modeStructure lengthAttenuation parameterFilling timeNormalized elastance1.54 GeV Damping RingEfinfrfGacc1bNbyEOo"zLsttfSol.54GeV2.856GHz40- 50 MeV/m4 buckets = 1.4 ns10 bunches1.0x 10-23mm2rc/33.0m0.50600nsec0.8Vm/pCTable 4 shows the parameters of the damping ring design for JILC. Thenonnalized emittance reqUired for the damping ring is 2.5 J..lIIlrad. The requireddamping time should be less than 2.5 msec. In order to achieve these extremely lowemittance and short damping time, the wigglers with the total length of 76 m iscombined to the ring. The 7.6 m-long wiggler unit is composed of the permanentmagnets, and the designed wiggler field is 1.8 Tesla, which seems to be a limit by theconventional permanent magnets.Table 4. Design parameters of the 1.54 GeV damping ringsTypeBeam energyCircumferenceBending magnetBending radiusNormalized emittanceDamping timeRepetition rateRf frequencyRF peak voltageBunch spacingNumber of bunchesNumber of bunch trainBunch currentTotal currentRm.s. bunch lengthEnergy spreadMomentum compaction factorNumber of Fono cells in arcWiggler lengthWiggler fieldEbCEoIbyEOtx/tyfrepfrfVrf1bNbtbIbItoto"z~E/EQpFOnOarc + Wiggler1.54GeV176.0ml.15T4.46m2.1x10-6 rad·m2.5/2.5 msec200Hz1.428GHz0.92MV2 buckets=1.4 ns10 bunches83.35 rnA218 rnA4.5mm0.76 x 10-32.2x 10-35476 m = 7.6 m/unit x 101.8TELECTRON LINAC OF TAF FOR LINEAR COLLIDER [1115]/157The arc is composed of 27 separated function FODO cells since the simple latticemakes it possible to obtain simplicity. The rf-frequency of ring cavities is chosen as1.428 GHz in L-band since the bunch length is 4.5 mm in the ring. The bunchseparation of each bunch is two buckets of the rf-frequency in the ring cavity. Thering contains 8 bunch trains of 10 bunches each. One bunch train is kicked out every5 ms. after the bunches circulate in the ring dUring 16 damping times.In order to decrease jitter. the following two extraction systems are designed: adouble kicker system and a feed-folWard system. The extraction kicker consists of apair of two kickers driven by the same pulser. The systematic error due to the jitter ofthe kicker-pulser will automatically be cancelled by two kickers. For random errorcorrection. the bunches are monitored by a position monitor installed at the exit ofthe extraction kickers. The random error between bunches in a bunch train iscorrected by the additional kicker installed at the injection part of thepreaccelerator linac. For the feed-foIWard system. the longer beam line is requiredin order that the control signals can catch up the bunches.1.0 GeV X-band LlnacThe tentative parameters of the 1.0 GeV X-band linac are listed in Table 5. Thestructure is a conventional 21C/3 mode. constant gradient disk-loaded structure. Acold model has been tested and prototypes of the structure for high-power test will beconstructed. The other type of structures are also studied to investigate thepossibility of these structures. for example damped cavities of higher order modesand the structures of the other modes.The rf sources for X-band klystrons are under developing. A 20 MW X-bandklystron so called XB-50 is under progress and the design work of a 50 MW X-bandklystron (XB-65) has been started.Table 5. Design parameters of X-band linac.Beam final energyBeam injection energyRF frequencyAccelerating gradientBunch spacingNumber of bunchesAccelerating modeStructure lengthAttenuation parameterFilling timeTAF PHASE-I LINACEfinEinjfrfGacctbNbLs'ttf2.5GeVl.54GeV11.424GHz100 MeV/m16 buckets=1.4 ns10 bunches21C/30.866 m (99 cell)0.5090nsecPhase-I linac is constructed at TRISTAN Nikko experimental hall. The rf-gunis under developing and a 240 kV thermionic gun is utilized as an electron source forthe phase-I linac. The linac consists of three subharmonic bunchers. prebunchers.158/[1116] S. TAKEDA ET AL.1W buncher and accelerating structures. The rf power from a pair of two SlAC-5045klystrons is fed into one accelerating structure. The following gradient will beobtained in the structures: 100 MeV1m in 0.6 m-Iong structure, 70 MeV1m in 1.5 m-long structure, and 50 MeV1m in 3 m-Iong structures. The pulsed electron beam fromthe gun is compressed by three sub-hannonic bunchers to generate a high currentsingle bunch. The single bunch is utilized for the wake field experiments and R&D forthe beam monitors. The rf frequencies of the SHB are 119 MHz, 238 MHz and 476MHz respectively. The number of electrons up to 1 x 1011 can be produced in a singlebunch.The requirement for the support and alignment system of the TAF differs fromthe ones for the accelerators in routine use. The components of the test acceleratorshould be easily replaced for the experiments. The support system of the phase-Ilinac consists of a 9 m long and 0.7 m wide table made of SUS-316L. The flatness ofthe table surface is adjusted and it is evaluated to be 36 J.1.m/9m. The components,such as electron gun, beam monitors, structures can be aligned within 50 J.1.m byputting on the table. The large components such as Helmholtz coils , Q-magnets andenergy analyzer magnet can be aligned within 100 JIDl.Figure 1. The Test Accelerator Facility (TAF)10I20I30I 40I SOm 60I70 80 90 100m1.5 GeV S-band Linac 1.0 GeV X-band Llnac..... TranapoItLlnl15.8 m 21.8 m 15.8 mELECTRON LINAC OF TAF FOR LINEAR COLLIDERFigure 2. TAF phase-I linac[1117]/159SHI SH8 SH8 Eleclron(471 MHz) (231 MHz) (11. MHz) Gunlunche, P,.bunch.,. I -\ ,R ft\~ M;ft!R RR,ft M~ ~ R!R ~ ft RR,~ RACKNOWLEDGEMENTo, 5000,A number of contributions to this conference contain more specific and detailedreports on the various aspects of the Test Accelerator Facility.REFERENCES1. Y. Kimura and K. Takata, Proc. 6th Symposium on Accelerator Science andTechnology (held at INS, 1987) p.313.2. Y. Kimura, Proc. European Particle Accelerator Conference (held at Rome,1988) to be published.3. S. Takeda, "Japan Linear Collider", Proc. of this conference.4.. K. Takata, Proc. of this conference.5. K. Yokoya, "Design parameter of the Japan Linear Collider", LC Note LC-89-44,unpublished, in Japanese, KEK, 19896. K. Yokoya, "Electron Energy Spectrum and Maximum Disruption Angle underMulti-Ph"()t~nBeamstrahlung", SIAC-PUB-4935 (March, 1989)7. K. Hirata; K. Oide and B. Zotter, "Synchrotron-Radiation Limit of theLuminosity in TeV Linear Colliders" CERN/LEP-TH/89-34 (April, 1989)8. K. Oide, "Final Focus 'System forTLC", SLAC-PUB-4806 (November, 1988)9. S. Kuroda et al., "On a Measurement of Strength of Final Focusing QuadrupleMagnet fora LinearCollider" , Proc. of this conference.10. H. Mizuno et al., "X-band Klystron Diode Test for Japan Linear Collider (JLC)",Proc. of this conference.11. H. Matsumoto et al., "RF High Gradient Experiment of an S-band 0.6 m Disk-Loaded Structure", Proc. of this conference.12. J. Kishiro et al., "A Test Stand of Microwave Free Electron Laser at KEK", Proc.of this conference.13. T. Higo et al., "X-band Accelerating Structure for Japan Linear Collider", Proc.of this conference.14. S. Kuroda et al., "1.54 GeV Damping Ring Designs of the Test AcceleratorFacility for Linear Collider", Proc. of this conference.15. H. Hayano et al.. "Fast RF Stabilization System for Test Accelerator Facilityfor Linear Collider", Proc of this conference.16. J. Urakawa et al., "Control System of the Test Accelerator Facility for Line~Collider", Proc. of this conference.17. N. Ishihara et al., "A Test Facility of Super-Accurate Alignment System for aLinear Col1ider", Proc. of this conference.18. M. Yoshioka, "Lasert:ron: A Pulsed rf Source Using a Laser-TriggeredPhotocathode", J. J. ofApp. Phys. 28, No.6, 1989, p.1079.

Electron Linac Of Test Accelerator Facility For Linear collider

Electron Linac Of Test Accelerator Facility For Linear collider

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