The CERN Proton Synchrotron started up in 1959, accelerating only protons from a 50 MeV Linac. Since then, it has evolved into a complex of nine machines, delivering in 1995 interleaved beams of protons, anti-protons, electrons, positrons and lead ions of various energies and intensities. It operates for about 7000 hours per year, sending beams to the SPS, to LEP via the SPS, and to four experimental facilities respectively supplied by the PSB, LEAR, LIL and the PS itself. Numerous original beam manipulation techniques are regularly applied and new ones are currently being implemented and tested to adapt the PS complex to its future role as the proton and ion injector for LHC. This paper summarizes the present status and describes the foreseeable future over the next twenty years

Simon, Daniel Jean

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 THE CERN PS COMPLEX : A VERSATILE PARTICLE FACTORYD.J. SIMON, for the PS StaffCERN, Geneva, SwitzerlandABSTRACTThe CERN Proton Synchrotron started up in 1959,accelerating only protons from a 50 MeV Linac. Sincethen, it has evolved into a complex of nine machines,delivering in 1995 interleaved beams of protons, anti-protons, electrons, positrons and lead ions of various en-ergies and intensities. It operates for about 7000 hoursper year, sending beams to the SPS, to LEP via the SPS,and to four experimental facilities respectively suppliedby the PSB, LEAR, LIL and the PS itself. Numerousoriginal beam manipulation techniques are regularly ap-plied and new ones are currently being implemented andtested to adapt the PS complex to its future role as theproton and ion injector for LHC. This paper summarizesthe present status and describes the foreseeable futureover the next twenty years.1. GENERAL DESCRIPTIONThirty seven years after its construction, the 200 m di-ameter combined function PS machine remains the heartof the PS Complex (fig. 1) [1]. With 3 RF systems (9.5,114 and 200 MHz), 4 injection and 4 extraction chan-nels, it routinely processes five types of particles (p+, p-,e+, e-, Pb53+) at momenta ranging from 0.6 to 26 GeV/cand at intensities between 108 and 2.5x1013 particles perpulse (ppp).The rest of the complex consists of:- Linac 2, producing protons from a duo-plasmatronsource followed by a 750 keV RFQ and 3 Alvarez tanksoperating at 200 MHz. Proton pulses are delivered at 50MeV every 1.2 s, with a length from 10 to 150 µs and anintensity of up to 180 mA,- Linac 3 [2], the last born of the PS machines, whichuses one 101 MHz RFQ accelerating Pb27+ ions up to 250keV/u, followed by a cascade of three IH structures (oneat 101 MHz, the other two at 202 MHz). The Pb27+ ionsare injected from an ECR source running in after-glowmode. After stripping by a carbon foil at the exit of thelinac, 25 µA of 4.2 MeV/u Pb53+ ions are routinely deliv-ered in 400 µs pulses.- The PS Booster (PSB), an assembly of four verticallystacked synchrotrons of 50 m diameter which acceleratethe linac beams respectively up to 1.69 GeV/c for protonsand 0.43 GeV/c/u for Pb53+.- The Antiproton Accumulation Complex (AAC) [3],made of the antiproton accumulator (AA), supplementedin 1987 with a collector (AC). Nine stochastic coolingsystems are used in each ring.- A 78.54 m circumference Low Energy Antiproton stor-age Ring (LEAR) [4]. It is equipped with six stochasticcooling systems, an electron cooler, a gas-jet target, andboth fast and ultra-slow extraction systems.- The LEP Pre Injector (LPI), consisting of a double 100Hz Linac (LIL-V and LIL-W) which sequentially pro-vides e- or e+ beams at 500 MeV to a 125 m long, race-track-shaped accumulator (EPA). LIL uses 16 travelingwave accelerating sections powered by five 3 GHzklystrons, 4 of which benefit from energy doublers calledLIPS.PSFigure 1. General map of the PS ComplexBeamLabelUser Particle Inj./ejmomentum[GeV/c]Inten-sity[ppp]RFharm.NrNo  ofbunchesεx , εy[µm](1)ε//[eVs]Bunchlength[ns]Inj./ej.straightsectionPeculiaritiesSFT SPS p+ 1.69 / 14 2.5101320,420420x5 11 / 7 0.1 5 42 / 16 Highest intensity beam, 5turn extractionSPP SPS-LEPe+ 0.5 / 3.5 2 1011 8 +2408 0.05 /0.01(2)0.01 4 92 / 16 Robinson wiggler tochange Je & JxSPN SPS-LEPe- 0.5 / 3.5 2 1011 8 +2408 0.05 /0.01(2)0.01 4 74 / 58 Robinson wiggler tochange Je & JxAA AAC p-productionp+ 1.69 / 26 1.6101310,12, ...,205 13 / 9 2 20 42 / 16 Transverse funneling,longitudinal merging andbatch compressionTSTAAC AAC p-transfersimul.p+ 1.69 / 3.5 2 1010 20, 6 1 4 / 1.5 0.5 70 42 / 16 Test beam for steeringadjustments of AA-PStransfer lineLEAR LEARp-physicsp- 3.5 / 0.6 1010 10 1 2 / 2 0.2 160 16 / 26 Deceleration on a digitalfrequency programPHYSE EastHallp+ 1.69 / 24 3 1011 20 N/A 3 / 5 0.2 N/A 42 / 61 Slow extraction (400ms)SFTION SPS Pb53+ 0.43 /5.1(3)2 108 20 20 1.7 /1.60.04(4) 11 42 / 16 Stripped to 82+ in thetransfer line to SPSPHYFE EastHallp+ 1.69 / 3.5 109 20 1-5 2.0/1.5 0.5 30 42 / 61 Low but precise intensity(1) εx,y = βγ σ2 / βx,y  (2) non normalized (3) [GeV/c/u] (4) [eVs/u]Table 1: Characteristics of the PS extracted beams2. THE DIFFERENT TYPES OF BEAMSThe detailed characteristics of the most representativebeams delivered by the PS are listed in Table 1.Protons.  The PSB is able to supply up to 3.1013 ppp in20 bunches at 1 GeV every 1.2 s. The PS machine accel-erates these beams and tailors their longitudinal charac-teristics to the specific needs of every user. Longitudinalemittance is blown-up in a controlled way, using the 200MHz RF systems. Bunch lengths and number of bunchesare changed with traditional debunching/rebunchingtechniques, as well as more involved “gymnastics” [1, 3],using the wide frequency range of the RF systems andthe flexibility of their controls [5]. Ultimately a largevariety of proton beams is routinely available:• debunched and slow extracted (~ 400 ms spills) at upto 24 GeV/c to the East Hall experiments,• bunched at 200 MHz and “continuously ejected” over 5turns at 14 GeV/c to SPS,• compressed into 1/4 of a turn (5 bunches) at 26 GeV/cand fast extracted to the AAC p- conversion target.In addition to feeding the PS, the PSB also providesintense (~3x1013) p+ beams at 1 GeV to the ISOLDEfacility.Antiprotons.  Antiprotons are collected at 3.5 GeV/cin batches of 5x107 from the AAC iridium target, sto-chastically cooled for 4.8 s in the AC, and then trans-ferred and stacked into the AA [3]. Up to 1012 p- can bestacked in the AA.A few times per hour, a single bunch of 2x109 to5x1010 p- is RF captured, ejected to the PS machine,decelerated down to 609 MeV/c and sent to LEAR. Thebeam can then be accelerated (< 2 GeV/c) or decelerated(> 100 MeV/c), and stochastic- and electron- cooling areextensively used (electron below 350MeV/c, stochasticabove) [4]. The LEAR beam can be used on an internalgas-jet target (typical coast life-time 30 h) or ejected byfast extraction (20-500 ns) or ultra-slow extraction (0.1-5h).Electrons and Positrons.  The 180 MeV LIL-V e-beam produces e+ in a tungsten target. The 12 ns leptonbeams are further accelerated to 500 MeV by LIL-W andlongitudinally stacked in one of the 8 EPA buckets.Whereas 5x1011 electrons are collected within a PS basicperiod of 1.2 s, it takes a full PS supercycle to accumu-late the same amount of positrons. Once every supercy-cle, the eight e+ (and 1.2 s later e-) bunches are fastejected to the PS, accelerated to 3.5 GeV with the 114MHz system, then transferred to the SPS in 2 batches of4 bunches spaced by 30 ms.Heavy ions.  The 4.2 MeV/u Pb53+ ions from Linac 3are first accelerated to 94.8 MeV/u in the PSB where achange of the RF harmonic number is needed to copewith the large variation of beam velocity. The PS accel-erates the ions using a dedicated, high sensitivity beamcontrol, then extracts the 20 bunches to the SPS. Theyare fully stripped to Pb82+ by a 1 mm thick aluminum foilin the transfer line.3. OPERATING MODESThe users of the PS Complex receive their own particlebeam according to pre-established sequences, called su-percycles. A PS supercycle is made of various magneticcycles, one or several cycles being allocated to each user.Fig.2 shows a typical supercycle of 19.2 s duration usedduring the lead ion physics run in 1995.For the pulsed machines, most of the parameters in theequipment - several thousands for PS or Booster - mustbe refreshed every cycle. This mode of operation, calledpulse to pulse modulation [5], has regularly increased incomplexity and flexibility during the past 20 years.Nowadays up to 24 potential beams can be prepared andinstantly put in operation as soon as required.The composition of the supercycle changes frequentlyduring a machine run according to the acceleratorschedule or even in real-time, to adapt to the users’ re-quests. For example, during the infrequent antiprotontransfers, the supercycle is temporarily modified.The scheduled running time of the PS Complex for 1996exceeds the all-time record of 6800 hours with about5600 hours devoted to antiproton physics (4900 in 1995).The beam availability is generally higher than 92% forSPS and LEP and 87 % for LEAR physics.duration:19.2sparticle Pb Pb Pb Pb p p pbar p p e + e - pPS user SPS SPS SPS SPSEASTHALL AAC LEAR MD AACSPSLEPSPSLEP AAC     destination PS PS PS PS PS ISOLDE PS ISOLDE MD PS PS ISOLDE MD  ISOLDE PS  ISOLDEPSsupercycleBoostersupercycleLPIactivitye+ accumulation                                                          &ejection to PSe- acc& ejecLILExp. AreaPhysicsFigure 2. Example of a supercycle used in fall 19954. FORESEEABLE FUTURELEP. LEP energy is scheduled to increase up to amaximum of 96.5 GeV/beam in the middle of 1999.Leptons need then to be delivered until the year 2000.Depending on the experimental request for the e-p optionin LHC [6], leptons will be again needed later during the21st century.LHC. Solutions have been designed to meet the strin-gent requirements of the beams for LHC with limitedmodifications to the PS complex.• For protons, the major issues are the increase of thePSB energy from 1 to 1.4 GeV and the installation ofnew RF systems in the PSB and in the PS [7]. Fol-lowing the initial demonstration of the validity of theproposed scheme in 1993 [8], a project was launchedwhich is due for completion for the start-up 1999.• For Lead ions the proposal is based on a low energy ionaccumulator ring, stacking multiple pulses fromLINAC 3 running at 10 Hz, and increasing beam den-sity in all planes with electron cooling. Some testshave already been performed [9] and more are foreseenbefore the shutdown of the LEAR facility, in 1997.SPS. Fixed target physics in the SPS North Area, testbeams and possibly neutrino physics with 450 GeV pri-mary protons will maintain a strong pressure for highintensity proton beams from the PS complex well after2005.PS Experimental facilities. Requests for beam-time inthe PS experimental area are increasing because of theneeds of calibration of the future LHC detectors. A proj-ect for upgrading the East Area has been submitted forapproval [10].The lepton beams from LIL and EPA are already indemand nowadays for LHC equipment testing, and willprobably be even more so as time goes by.The ISOLDE physics community foresees requests formuch beam time, especially if the first stage of radio-active ion accelerators experiment (REX) at CERN livesup to its promises.Antiproton facility. The present low energy antiprotonfacility with its 3 dedicated machines (AC, AA andLEAR) will be stopped at the end of 1996. A low-costinstallation called the “Antiproton Decelerator” (AD)[11] is proposed to continue the antihydrogen studies atCERN. It would collect, cool, decelerate and eject about1/10th of the present flux of antiprotons to a small num-ber of experiments. If approved in 1996, data takingcould begin during the first half of 1999.REFERENCES[1] R. Billinge for the PS Staff, ”The CERN PS Complex: AMultipurpose Particle Source”, Proc. of XIIth Intl. Conf.on High Energy Acc., 1983.[2] H.Haseroth, “The CERN Heavy-ion Facility”, Proc ofEPAC 94, London, 1994.[3] G. Carron et al., “The CERN Antiproton AccumulatorComplex (AAC) : Current Status and Operation for theNineties.” Proc. of XVth Intl Conf. on High Energy Acc.,Hambourg, Germany, 20-24.7.92[4] E. Asseo et al., “Performance Update of LEAR”, Proc.EPAC92, Berlin, 1992, Vol.1 p. 447[5] J. Boillot, B.Frammery, E.Wildner, “The CERN-PS Con-trols System Operational Aspects”, Proc. of EPAC 94,London, 1994, Vol.3 p.1782.[6] The LHC Study Group, "The Large Hadron Collider: Con-ceptual Design", CERN/AC 95-05 (LHC)[7] R. Cappi et al. "Beams in the PS Complex during the LHCEra", CERN/PS 93-08 (DI), LHC Note 232 rev.[8] K. Schindl for the PS Staff, "Partial Test of the PS Com-plex as LHC Proton Injector", Proc. of EPAC 94, London,1994, Vol.1 p.500.[9] S. Baird et al. “Measurement of the lifetime of Pb52+, Pb53+and Pb54+ beams at 4.2 MeV/c/u subject to electron cool-ing”, Phys. Lett. B 361 (1995), p.184[10] L.Durieu, J.-Y.Hémery “EHNL_3” CERN Internal NotePS/PA Note 96-10[11] S.Maury (editor), “The Antiproton Decelerator, A Simpli-fied Antiproton Source (Feasibility Study)”, CERN/PS 95-36(AR)

The CERN PS complex: a versatile particle factory

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