Braun, H

Chautard, F

Delahaye, J P

Madsen, J H B

Riche, A

Rinolfi, Louis

CERN Document Server

12/9/94 OCR OutputGeneva, Switzerland17th International Linac Conference, Tsukuba , Iapan, August 21 — 26, 1994results.the main limitations for the CTF. The simulation results are compared with the experimentalSpecial attention has been given to space charge and transverse wake field effects, which areimplemented from 1993 up to now. Simulations are mainly done with the code PARMELA.Here we present the beam dynamics simulations for the different CTF configurationsservice in 1991 with the main objective to study the drive beam generation.(average) accelerating gradient at 30 GI-Iz. The CLIC Test Facility (CTF) was brought intolatter will consist of bunches of high charge and short pulse length in order to get the 80 MV/ mThe CERN Linear Collider (CLIC) requires two beams: the main and the drive beam. TheAbstractA. Riche, L. RinolfiH. Braun, F. Chautard, ].P. Delahaye, ].H.B. Madsen,BEAM DYNAMICS FOR THE CLIC TEST FACILITYC _ T. 5wBSCERN-PS~94-31CLIC Note 243°E“N”S M “‘P’llIlllllIIIIlIlllllllIlllllllllllllllillllCERN LIBRARIES, GENEVACERN - PS DIVISIONCERNEUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHvoltage when it is zero on the photo-cathode. This latter wasFig. 1 CTF line in 1995 OCR Outputof laser pulse hits the photo-cathode minus the phase of RFThe initial phase is defined as the phase where the centreTRS: CLIC Transfer Structure CAS: CLIC Accelerating Structure J;However discrepancies appeared at high charge.SNF: Solenoid LAS: 45rn Accelerating Structure Qi: Quadrupuleseffect and at low charge, both codes gave the same results.MAFIA code was extensively used [4]. Without space chargeQI Q3The RF gun was modelled with PARMELA code, but alsoperformed with TRANSPORT and PARMHA codes [1].TISof TRS (4 mm diameter iris). Several simulations have beenIDGTEI CIIIIIBSQI. °2 Qlexit of the LAS matches the beam emittances to the entrance LAS Il I:*‘•· acm. auuctr 2 2 § EE ;(Q1 to Q4) were not installed. The quadrupole triplet at the5 =that the booster, the bunch compressor and the 4 quadrupolesThe simplified 1993 CTF layout is shown in Fig. 1 exceptwas not possible to compare all parameters with high charge.CTF line in 1993 results were consistent with the simulation results although itox and ex have been measured at 3 nC. The experimentalsimulations for wake fields are performed accordingly.obtained from a bunch uain, at lower charge, and (mm.mrad) 417high charges. However the 30 Gl-Iz power generation is 150428Norm. rms emittance I exbunch measurements characterise the CTF performance at 7.4Charge8.2Qf (nC)performed for a single bunch and comparison with singlec,.· (mrad)Divergence 1.3be implemented in 1995. All PARMELA simulations are¤y(mm) 1.6bunch compressor at ll MeV has been finalised [3]. It will1.8 0.9Transverse size I ¤x(mm)energy up to 80 MeV. Recently the design of a magnetic1514.6FWHH (ps)connected to the travelling-wave section allows to raiseoz (mm)Length 1.86and feeds the RF gun and the booster. The first one1.8Energy dispersion I op (%)travelling wave section [2]. A second klystron was installedMomentum 58p (MeV/c) 57.9which raises the beam energy to ll MeV before thench at the TRS1994, a new 4 cell standing wave cavity (booster) was addedanother 30 GHz CLIC Accelerating Structure (CAS). InRF power 5.85generated and a probe beam to check acceleradon withoo (deg) 4545Initial phaseTransfer Structure (TRS) where the 30 GHz RF power is100100Max. cathode E field I Eo (MV/m)(4 MeV), a long u·avelling·wave section (60 MeV), a CLICRF gunIn 1993, the CTF [1] was mainly composed of an RF gun1010Ernitted charge I Qo (nC)IntroductionFW1-IH (ps)om (ps) 3.8Durationexperimental results.12 10Total (mm)for the CTF. The simulation results are compared with theom (mm)Spot simtransverse wake field effects, which are the main limitationsSpecial attention has been given to space charge andSirnul. I Exper.now. Simulations are mainly done with the code PARME..A.different CTF configurations implemented hom 1993 up toSimulation and Experimental Data for 1993Here we present the beam dynamics simulations for theTABLE 1with the main objective to study the drive beam generation.CLIC Test Facility (CIF) was brought into suvice in 1991between PARELA simulations and experimental results.the 80 MV/m (average) accelerating gradient at 30 GHz. Theused. Table 1 gives a comparison, for a charge of 10 nC.bimches of high charge and short pulse length in order to getsimulations, both Gaussian and uniform distributions werethe main and the drive bmm. The latter will consist oftransverse distribution was not measured and forThe CERN Linear Collider (CLIC) requires two beams:almost all the photo-cathode was illuminated. Howevu the12 mm in diameter. The optics was made in such a way thatAbstractCERN, CH · 1211 Geneva 23H. Braun, F. Chautard, J.P. Delahayc. J.H.B. Madsen, A. Richc, L. RinoltiOCR OutputBEAM DYNAMICS FOR THE CLIC TEST FACILITYtransverse wake potentials of the booster, the LAS and theeffects. To estimate the magnitude of these effects the dipole. OCR Output30 GHz power production is given by transverse wake field also been designed and will be implemented after the firstIn the present layout the most serious limitation for energy up to 20 MeV. Additionally, a spectrometer line hasStructure (TRS). The bunch compressor is designed for anAverage electric field in CAS 73 MV/m get a good transmission up and through the CLIC TransferPeak Electric field in CAS on axis 103 MV/m between 0 and 10 nC. The optimisation is done in order to79 MV/mAverage electric field in ’I`RS study the CTF beam dynamics [3] for charges varyingPeak electric field in TRS on axis 110 MV/m spread due to beam loading. Simulations were performed to30 GI-lz power at TRS 60 MW (peak) foreseen for LAS. The higher gradient will lower the energy2.8 nC/bunchcharge at TRS input input of LAS. The installation of an RF pulse compressor is8 pse- pulse length (FWI-IH) (Fig. 1). Quadmpoles Q1 to Q4 will match the beam at theBunch uain 24 bunches acceleration in the gun and a 3 dipole magnetic chicaneThis compression will be achieved using off cresttoday, are the following: be compressed down to the required pulse length (o s 3 ps).The peak perfomiances, for power generation, achieved pulse (o = 8 ps) and downstream of the booster, bunches willexit, 16 nC at the LAS exit and 7 nC downstream of TRS. the photo-cathode will be illuminated with a longer laserpeak performance, for a single bunch, is 23 nC at the booster accelerating structure. ln order to minimise the first effects,bunch at the charge value used with the bunch vain. The charge effects at low energy and the waketields in the longPARMELA simulations and experimental results for a single The main limitations in the present CTF are the spacemeasurements. Finally there is a good agreement betweenThe measured horizontal emittance is scaled from FWHI-I CTF line in 1995(mm.mrad) 40Norm. rms emittance 42 39 transverse wake fields.Charge 2.8 Fig. 2 Emittance growth from booster to TRS due toQf (nC) I 2.8Divergence Z-uh (mlo,· (mrad) I 1.2o z 4 n • in0.5¤v(mm) I 0.4Transverse size 0.5cx(mm) I 0.2 tor'FWI-IH (ps) I 8Length 1.1cz (mm) I 1.r¤"Energy dispersion cp (%) I 0.4 | <0.2Momentum p(Mev/c) | 81.8 | 80Bunch at the TRS1e°Phase ¤ (d¢z> I 90 I 90mlElectric field on axis E(MV/m) I 70 I 70&•¤ dndd S @1 ¤¤·u¤tur·• quad. trlpht $@1 knumnBmtsrRF power Pr; (MW) | 5.85 I 6Initial phase %(deg) | 45 | 20-50Max. cathode E field E(,(Mv/m) I 100 | 100RF gun ABCI is limited to axially symmeuic suuctures.Sim. I Ex and of RF input/output couplers are not included, sincediscontinuities in the vacuum chamber, like pumping ports,velocity over one cell. Also the contributions ofSimulation and Experimental Data for 1994cannot be applied there due to the large change of particleTABLE 2included in the calculations. The wake potential conceptto those in 1993.explained by the fact that contributions of the RF gun are notresults. The laser pulse and the photo-cathode are identicaltotal emittance (cf. table 2). This discrepancy could maybefor a charge of 2.8 nC and compared to the experimentalthe observed effects, since it xcounts for only one fifth of thelow energy. PARME..A simulations are reported in Table 2However, the computed growth is not sufficient to explainbooster allows the minimisation of the space charge effects atshown (Fig. 2). Note the fast growth in the 30 GHz structure.are not yet installed and are replaced by one solenoid. Theg1·owth of a uain of 24 bunches with 2.8 nC bunch charge isthat the bunch compressor and the 4 quadrupolcs (Q1 to Q4)multibunch waketield effects. The resulting emittanceThe simpliticd 1994 CTF layout is shown in Fig. 1 exceptthe results were put in a self made tracking program forCLIC suucture were computed with the code ABC1 [5] and[5] Y.l·I. Chin, "User’s Guide for ABCI," CERN/SL/94-02(AP) OCR Outputafter compression.the CLIC test Faci1ity“, CERN/PS 93-27(RF). CLIC Note 205.Fig. 4 Longitudinal phase space for 10 nC,[4] S. Liitgert, "MAFIA simulations of the multicell RF gun forFacility", CERN/PS/94-30 (LP). Also CLIC Note 240.[31 F. Chautard, L. Rinolfi, "Bunch compressor for the CLIC Test-I¤ -7A -5 -1.5 ¤ 1.5 I 7.5 10linear collider test facility (CTF)". CERN/PS/94-17 (LP).Wilson, W. Wuench., "Performances obtained with the CERNMadsen, A. Riche, L. Rinolfi, J. Sladen, G. Suberlucq, L[21 R. Bossart, H. Braun, 1.P. Delahaye, K. Geissler, I.C. Godot,J.NIM Sec.A340( l994),pp139-145. Also CERN/PS/93-32 (LP).status and future of the CERN linear collider test facility'[1] J. P. Delahaye, J. Madsen, A. Riche, L. Rinolfi. "PresentReferencesRemmer for their support in computational code facilities.We would like to thank B. Mouton (Orsay) and W.Element=23 Z= 2.5970m Acknowledgementhigh charges and the drive beam generation.tlterefore to take action to reach the CLIC figures for thebefore compression. now possible to understand better the present limitations andFig. 3 Longitudinal phase space for 10 nC, giving a rather good agreement with the experiments, it isWith the different simulations perfomred on the Cl'F,-|¤ -7..5 —$ -1.5 U 25 5 1: IDConclusione,=l77, e,=l30at the entrance of TRSat the exit of the bunch compressor c,=132, ey-60e,=s,.=70.at the exit of the boosterg,.-:%:64.at the exit of the gum:RMS norm. emittances [mmmrad]at the entrance of ’I`RS x’=0.7, y’=0.6at the exit of the bunch compressor x'=2.0, y`=6.8x’=y’=70.at the exit of the boosterx’=y’=3l.at the exit of the gun:RMS transverse divergences [mrad]]Elcment=17 Z= 1.7370m at the entrance of TRS x=l.4, y=l.3at the exit of the bunch compressor x=4.5, y=l.0x=y=4.7at the exit 0f the booster0.88 mm, i.e. the compression factor is 4. x=y=4.5at the exit of the gun:respectively l3° and 3.2° corresponding to 3.6 mm and RMS transverse sizes [mm]and after compression. The beam extents in phase are 1.1at the entrance of TRSFigures 3 and 4 show the longitudinal phase space before 2.6at the exit of the bunch compressorefficiency is kept at its maximum from the RF gun to TRS. 3.6at the exit of the boosterentrance of the bunch compressor. The transmission 1.6at the exit of the gun:spread is 3.6% for a beam extent of l3° at 10 nC at the Momentum spread: 8p/p [%]phase where the RF slope is large. The resulting energy 80at the entrance of TRScrest of the RF where the energy spread is minimum to a llat the exit of the bunch compressorThis correlation is obtained by moving the beam from the llatthe exit oftheboosterbunch have a lower momentum than the ones in the tail. 4.5at the exit of the gun:the energy spread is maximum. Particles in the front of the Momentum: P [MeV/clbetween the phase and the momentum of the bunch such thatPARMELA Output Data for 10 nCthe gun and the booster are chosen to get a good correlationTABLE 3the divergence of the beam induced by the gun. The phase ofbeam at the entrance of the btmch compressor to compensateTable 3 presents the simulation results hom PARMELA.The solenoid is optimised in order to get a convergent

Beam dynamics for the CLIC test facility

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