As the pre-injector of the LHC injector chain, the proton linac at CERN is
required to provide a high-intensity (180mA) beam to the Proton Synchrotron
Booster. The results of measurements at this intensity will be presented.
Furthermore, the linac is now equipped with bunch shape monitors from INR,
Moscow, which have allowed the comparison of the Alvarez tank RF settings with
simulations.Comment: LINAC 2000, TUC14, 3 pages, 5 figure

Feschenko, A.

Hill, C. E.

Liou, A.

Lombardi, A.

Scrivens, R.

Vretenar, M.

English

arXiv

As the pre-injector of the LHC injector chain, the proton linac at CERN is required to provide a high-intensity (180mA) beam to the Proton Synchrotron Booster. The results of measurements at this intensity will be presented. Furthermore, the linac is now equipped with bunch shape monitors from INR, Moscow, which have allowed the comparison of the Alvarez tank RF settings with simulations

Feschenko, A V

Hill, C E

Lombardi, A M

Liou, A

Scrivens, R

Vretenar, Maurizio

CERN Document Server

EUROPEAN ORGANISATION FOR NUCLEAR RESEARCHCERN - PS DIVISIONCERN/PS 2000-053 (PP)TESTS OF THE CERN PROTON LINAC PERFORMANCE FORLHC-TYPE BEAMSC.E. Hill, A. Lombardi, R. Scrivens, M. VretenarCERN, CH-1211 Geneva 23, SwitzerlandA. Feschenko, A. LiouInstitute for Nuclear Research, Moscow, 117312 RussiaAbstractAs the pre-injector of the LHC injector chain, the proton linac at CERN isrequired to provide a high-intensity (180mA) beam to the Proton SynchrotronBooster. The results of measurements at this intensity will be presented.Furthermore, the linac is now equipped with bunch shape monitors from INR,Moscow, which have allowed the comparison of the Alvarez tank RF settingswith simulations.Presented at the XXth International Linac Conference,21-25 August 2000, Monterey, California, USAGeneva, Switzerland18 August 2000TESTS OF THE CERN PROTON LINAC PERFORMANCE FORLHC-TYPE BEAMSC.E. Hill, A. Lombardi, R. Scrivens, M. VretenarCERN, CH-1211 Geneva 23, SwitzerlandA. Feschenko, A LiouInstitute for Nuclear Research, Moscow, 117312 RussiaAbstractAs the pre-injector of the LHC injector chain, theproton linac at CERN is required to provide a high-intensity (180mA) beam to the Proton SynchrotronBooster. The results of measurements at this intensity willbe presented. Furthermore, the linac is now equipped withbunch shape monitors from INR, Moscow, which haveallowed the comparison of the Alvarez tank RF settingswith simulations.1  INTRODUCTIONLinac 2 has been in operation since September 1978and routinely supplies protons during 6700 hours ofoperation per year. The machine consists of aDuoplasmatron proton source at 90 kV, a 750 keV RFQ,and three Alvarez tanks accelerating the beam to 50 MeV.In normal operation a 170 mA proton beam is injectedinto the Proton Synchrotron Booster (PSB) with a pulselength up to 150 µs, at a repetition rate of 0.8 Hz [1].From 2005 onwards, the linac will function as the pre-injector for the Large Hadron Collider (LHC), for which180 mA is desired [2]. This is difficult to achieve becausethe longitudinal beam dynamics are strongly space-chargelimited at the low energy end of tank 1.Within the framework of upgrading towards thisintensity the 750 kV Cockcroft-Walton was replaced withan RFQ in 1993. More recently, three Bunch ShapeMonitors (BSMs) have been installed, to allow the studyof the beam dynamics of the Alvarez tanks.2  HIGH CURRENT TESTSThe optimisation of the linac to produce higher outputcurrents was performed during 1999. A comparison of thereadings of the current transformers along the length ofthe linac, for the high current case and during normaloperation, is given in Figure 1. It is clear that the principlegain in this case was the 32% higher current from thesource. From this higher current, the improvement of 10%was possible at the end of the linac, and the greater lossesin the transfer line (after the linac) led to a finalimprovement at the entrance of the PSB injection line of6%.The large losses from TRA02 to TRA06 are mostly dueto the loss of the H2+ beam at the entrance of the RFQ.The beam parameters were verified with the single-shotemittance measurement and the spectrometer at thebeginning of the PSB injection line. No difference in theemittance or energy spread was seen between the highcurrent case and the normal operation beam.Figure 1. Beam current measured along the proton linac,for the normal operation beam, and during tests of highcurrent. TRA02:After Source, TRA06:after RFQ; TRA10:after accelerator; TRA20-60; transfer line to the PSB. 3  BUNCH SHAPE MONITORSThe principle of the Bunch Shape Monitor (constructedby INR, Troitsk) has been fully described in [3]. In short,a bunched ion beam impinges on a wire target held at highvoltage, releasing secondary electrons that retain theinitial bunch structure of the ion beam. The electrons areswept by a RF deflecting field, which allows the relativeion beam intensity at a given phase to be measured. By re-phasing the RF deflecting field with respect to the linacRF, the ion density distribution can be reconstituted.On Linac 2, three BSMs are now installed (see Figure2). The first two are standard devices placed in the inter-tank sections between tanks 1-2 and 2-3. At the output ofthe linac, the 3D-BSM allows selection of a transverseportion of the beam and the measurement of the bunchshape in a single-shot, by an array of charge collectors.The 3D-BSM was installed in 1996 [4], and the results ofits first measurements on the proton beam are given in [5].TRA02 TRA06 TRA07 TRA10 TRA20 TRA30 TRA40 TRA50 TRA60050100150200250300350Beam current (mA)Current Transformer During High Current Tests During Normal OperationFigure 2. Scheme of the CERN 202 MHz Linac 2 Alvareztanks, with the locations of the three BSMs.The settings of the Alvarez tanks were studied bymeasuring the longitudinal movement of the bunch as afunction of the RF phase and amplitude. By treating onlythe bunch centre, the effects of space charge in thecalculation of the motion of the bunch are avoided. Thebunch motion was calculated using the simulation toolDELTAT, based on the procedures given in [6].The measurements were performed on the linac withthe normal operational beam, in a time window from 25-50 µs after the start of the proton pulse from the source.Measurements have shown that before this time, theproton beam is not well stabilised (due to current variationand the time constant of the RF feedback loops.2.1 Tank 1Measurements at the output of tank 1 have not beencompleted. The wire target of the IT-BSM is held at highvoltage, but the current being drawn is too high for the HTsupply (probably due to small discharges in vacuum). Therectification of this problem requires opening the vacuumof the Alvarez structure, which cannot be performed untilthe winter 2000-01 shutdown.The comparison of the measured bunch position inphase and the simulation is complicated by the degrees offreedom (the unknown RF amplitude and the unknownoffset in the bunch phase). The measured data are shownin Figure 3 along with curves from a simulation, fordifferent RF levels of the tank. Note that the measureddata can be arbitrarily offset vertically. The simulationresults in the same gradient as the measurement, for RFtank levels of 0.95A0 , 1.10A0 and 1.15A0 (where A0 is thenominal RF level). The power requirements to run thetank at 10% higher than the nominal values could not befulfilled by the RF system, so the 0.95A0 line would be themost likely.It is then estimated that the beam enters the tank with aphase of -30o during normal operation, whereas the initialsynchronous phase of the tank is -35o (where 0o is the crestof the RF wave).With no second measurement of the beam of the bunchposition as a function of the RF level, the results are notyet conclusive.2.2 Tank 2With measurements of the bunch position in phase as afunction of the tank 2 RF phase and amplitude, thecomparison of the simulated and measured data is mucheasier. In Figure 4a the measured data are compared to thesimulations using DELTAT. The gradient of the measureddata is very similar to that of the results obtained for aninput phase of –10o, compared to the nominal synchronousphase of –25o.The bunch centre as a function of the tank 2 RF phaseis given in Figure 4b, and is shifted along the x-axis suchthat the nominal phase corresponds to –10o. Thesimulation fits the measured data well.areFigure 3. Measured data for the phase position of thebunch at the output of tank 1 as a function of the RF phaseof tank 1. Curves show simulated bunch position as afunction of the RF phase, for different RF amplitudes.Figure 4. Measured data for the phase position of thebunch at the output of tank 2 as a function of a) the RFamplitude and b) the RF phase. Curves show simulatedbunch phase position.2.3 Tank 3The measurements with the 3D-BSM located after tank3 have concentrated on the longitudinal dynamics, and thetransverse distribution of the beam is not considered here.As the electron bunch is measured with an array oftransverse charge collectors, the resolution during the-80 -60 -40 -20 0 20 40 60-230-220-210-200-190-180-170Nominal Phase Measured Data Sim 0.95A0 Sim 1.0A0 Sim 1.05A0 Sim 1.1A0 Sim 1.15A0Bunch centre (degrees)RF Phase of Tank 1 (degrees)0.900 0.925 0.950 0.975 1.000 1.025 1.050 1.075 1.100 1.125 1.150-230-220-210-200Measured Data φ=-35o φ=-30o φ=-25o φ=-20o φ=-15o φ=-10oBunch centre (degrees)RF Level of Tank 2 (normalised)-40 -35 -30 -25 -20 -15 -10 -5 0 5 10-220-210-200-190 NominaloperatingphaseMeasured Data 0.96A0 0.98A0 1.00A0 1.02A0 1.04A0Bunch centre (degrees)RF Phase of Tank 2 (degrees)measurements reported here is approximately 4.5o, whichis 2 to 4 times lower than the resolution of the BSMslocated between the tanks. Improving the resolutionresults in a narrower total range of phases that can bemeasured.The measurements of the phase position of the bunch asa function of RF amplitude and phase are given in Figure5. The simulations are in good agreement with themeasured data based on an input phase of –40o comparedto a nominal synchronous phase of –25o, and with a RFfield level 6% higher than the nominal value.Figure 5. Measured data for the phase position of thebunch at the output of tank 3 as a function of a) the RFamplitude and b) the RF phase of Tank 3. Curves showsimulated bunch position. 4  CONCLUSIONSIt has been  demonstrated that the CERN lLinac 2 canprovide the 180 mA beam required for the LHC injectorchain. The larger resulting losses in this case mean thatthe beam is not at present used in routine operation at thePS complex.The BSM data compiled for tank 1 are incomplete andrequire the repair of the BSM and the measurement of thebunch phase position as a function of RF amplitude beforefinal conclusions can be drawn.Tank 2 data are in excellent agreement with simulationsof the bunch centre. Tank 3 data shows good agreementwith simulations but with a RF level much higher than thenominal value.This exercise provides an excellent starting point forfurther simulation with a macro-particle code (e.g.PARMILA) to provide more complete understanding ofthe dynamics and limitations of the structure with highercurrents. This should allow the losses at higher currents tobe reduced for routine operation as the LHC preinjector.REFERENCES[1] C.E. Hill, A.M. Lombardi, E. Tanke, M. Vretenar,Present Performance of the CERN Proton Linac,Procs. of the 1998 Linear Accelerator Conf., Chicago,IL, p. 427 (1998).[2] K.H. Schindl, The Injector Chain for the LHC,Workshop on LEP-SPS Performance, Chamonix, Jan.1999, CERN/PS 99-018(DI).[3] Feschenko A.V., Ostroumov P.N., Bunch ShapeMeasuring Technique and Its Application for an IonLinac Tuning, Proc. of the 1986 Linear AcceleratorConference, Stanford, 2-6 June, 1986, pp.323-327.[4] S.K. Esin, V.A. Gaidash, A.V. Feschenko, A.V.Liiou, A.N. Mirzojan, A.A. Menshov, A.V. Novikov,P.N. Ostroumov, O. Dubois, H. Kugler, L. Soby, D.J.Williams, A Three Dimensional Bunch ShapeMonitor for the CERN Proton Linac, Proc. of the1996 Linear Accelerator Conference, Geneva,Switzerland.[5] A.V. Feschenko, A.V. Liiou, P.N. Ostroumov, O.Dubois, H. Haseroth, C. Hill, H. Kugler, A.Lombardi, F. Naito, E. Tanke, M. Vretenar, Study ofBeam Parameters of the CERN Proton Linac Using aThree Dimensional Bunch Shape Monitor, Proc. ofthe 1996 Linear Accelerator Conference, Geneva,Switzerland.[6] K. Crandall, RF Adjustment Techniques UsingRelative Measurements, CERN PS/LR/Note 79-3(1979).0.94 0.96 0.98 1.00 1.02 1.04 1.06 1.08 1.10 1.12 1.14-220-210-200-190-180-170Measured Data φ=-200 φ=-250 φ=-300 φ=-350 φ=-400Bunch centre (degrees)RF Level of Tank 3 (normalised)-80 -70 -60 -50 -40 -30 -20 -10 0-220-210-200-190-180-170 NominaloperatingphaseMeasured Data 1.00A0 1.03A0 1.04A0 1.05A0 1.06A0Bunch centre (degrees)RF Phase of Tank 3 (degrees)

Tests of the CERN proton linac performance for LHC-type beams

As the pre-injector of the LHC injector chain, the proton linac at CERN is required to provide a high-intensity (180mA) beam to the Proton Synchrotron Booster. The results of measurements at this intensity will be presented. Furthermore, the linac is now equipped with bunch shape monitors from INR, Moscow, which have allowed the comparison of the Alvarez tank RF settings with simulations.As the pre-injector of the LHC injector chain, the proton linac at CERN is required to provide a high-intensity (180mA) beam to the Proton Synchrotron Booster. The results of measurements at this intensity will be presented. Furthermore, the linac is now equipped with bunch shape monitors from INR, Moscow, which have allowed the comparison of the Alvarez tank RF settings with simulations.As the pre-injector of the LHC injector chain, the proton linac at CERN is required to provide a high-intensity (180mA) beam to the Proton Synchrotron Booster. The results of measurements at this intensity will be presented. Furthermore, the linac is now equipped with bunch shape monitors from INR, Moscow, which have allowed the comparison of the Alvarez tank RF settings with simulations.As the pre-injector of the LHC injector chain, the proton linac at CERN is required to provide a high-intensity (180mA) beam to the Proton Synchrotron Booster. The results of measurements at this intensity will be presented. Furthermore, the linac is now equipped with bunch shape monitors from INR, Moscow, which have allowed the comparison of the Alvarez tank RF settings with simulations.As the pre-injector of the LHC injector chain, the proton linac at CERN is required to provide a high-intensity (180mA) beam to the Proton Synchrotron Booster. The results of measurements at this intensity will be presented. Furthermore, the linac is now equipped with bunch shape monitors from INR, Moscow, which have allowed the comparison of the Alvarez tank RF settings with simulations

Tests of the CERN Proton Linac Performance for LHC-Type Beams

Abstract

Similar works

Full text

Available Versions

CERN Document Server

CERN Document Server

CERN Document Server