Status of the LIU project and progress on space charge studies

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2 Status of the LIU project and progress on space charge studies S. Gilardoni CERN BE/ABP In collaboration with: J. Coupard, H. Damerau, A. Funken, B. Goddard, K. Hanke, A. Lombardi, D. Manglunki, M. Meddahi, B. Mikulec, G. Rumolo E. Shaposhnikova, M. Vretenar and H. Bartosik, E. Benedetto, G. Bellodi, M. Bodendorfer, G.P. di Giovanni, V. Forte, A. Huschauer, R. Wasef EuCARD2/XBeams Workshop on Space Charge Trinity College, Oxford, 23rd- 27th March 2015

3 Output energy LHC injectors upgrade Goals Present LIU (2019) Proton flux / Beam power 50 MeV 160 MeV 1.4 GeV 2.0 GeV Linac2 PSB Linac4 PSB 26 GeV PS PS 450 GeV SPS 7 TeV LHC / HL-LHC The LHC Injectors Upgrade should plan for delivering reliably to the LHC the beams required for reaching the goals of the HL-LHC. This includes LINAC4, the PS booster, the PS, the SPS, as well as the heavy ion chain (This is the mandate Upgrade of Brightness) + determine possible improvements for high intensity beams.

4 LIU proton target HL-LHC beam parameters 25 ns N (x p/b) e (mm) B l (ns) Achieved in (std) 1.5 HL-LHC Injectors must produce 25 ns bunch spacing proton beams with about double intensity and even more than double brightness A cascade of improvements is needed across the whole injector chain to reach this target

5 LHC and Injectors 50 ns (will be 25 ns in 2015) 1 SPS batch (144 bunches) 1 PS batch (36 bunches) Abort gap LHC km bunches 50 ns = Field in main magnets = Proton beam intensity (current) = Beam transfer To LHC 450 GeV SPS 26 GeV PS PSB 1.4 GeV 1.2 seconds Time

6 LHC25(50)ns Production Scheme Production scheme: a) Double batch injection from PSB (4 + 2 bunches, 6 bunches for PS at h=7) b) Up to 4 batches of 72 bunches each transferred to the SPS (288 bunches) Transverse emittance produced in the PSB, longitudinal in the PS Multi-turn proton injection in PSB RF gymnastics in PS: - Triple splitting - Acceleration - 2 x Double splittings - (1 Double splitting for 50 ns) - Bunch rotation 3 RF systems in PSB 5 RF systems in PS 2 RF systems in SPS

7 BCMS Batch Compression, Merging and Splitting in PS h = LHC 25(50)ns BCMS Production scheme: a) Double batch injection from PSB (4 + 4 bunches, 8 bunches for PS at h=9) b) Up to 5 batches of 48 bunches each transferred to the SPS (240 bunches) Transverse emittance produced in the PSB, longitudinal in the PS - Multiturn proton injection in PSB with shaving - RF gymnastics in PS: - Batch compression - Bunch merging h = Triple splitting - Acceleration - 2 x Double splittings (1 Double splitting for 50 ns) - Bunch rotation 4 bunches +4 bunches h = 9 h = 21 7

8 Schemes 25 ns Catalogue of Possible production schemes - 25 ns PSB PS bunches RF gym. in PS RF gym. at injection RF gym. at extraction b/train to SPS SPS injections 3-spitting (standard scheme) /3 /2 / BCMS C/3 /2 / BCS C /2 / b+4e /2 /2 / / Splitting C Batch Compression + Merging Acceleration to 26 GeV/c

9 SPS PS PSB Beam parameters N (10 11 p) ε x,y (mm) E kin (GeV) Waiting time (s) Lattice ΔQ x,y Achieved Triplet (0.51,0.61) LIU Triplet (0.55,0.66) HL-LHC Triplet (0.58,0.69) Achieved FDODF (0.24,0.31) LIU FDODF (0.16,0.28) HL-LHC FDODF (0.18,0.30) Achieved FDFD (0.05,0.07) LIU HL-LHC FDFD (0.09,0.16) FDFD (0.10,0.17)

10 Challenges of the production schemes High intensity injected in PSB: - every PSB bunch is split 12 times (to get finally 72 bunches at 25 ns spacing) - Space-charge issue*. - Today limited brilliance due to multiturn injection process Long waiting time at PS injection (1.2 s): - Space-charge issue*. - Headtail instability. Long waiting time at SPS injection (up to 4 x 3.6 s) Many RF systems involved: - Longitudinal instabilities and limitations to be overcome in all the machines Beam quality is an issue: - PS-SPS very sensitive to difference in relative bunch population * See F. Schmidt presentation - LHC final luminosity very sensitive to degradation of transverse emittance

11 PSB: Double beam brightness with 160 MeV H - injection from Linac4 Acceleration to 2 GeV with upgraded main RF systems or replacement by Finemet cavity based RF system, and new main power supply PS: Increase brightness with 2 GeV injection from the PSB Feedback systems: Newly installed wide-band longitudinal feedback against Coupled Bunch Instabilities Transverse feedback against headtail and e-cloud instabilities SPS: Power upgrade of the main 200 MHz RF system (plus double available 800 MHz voltage, and new LL RF system) Electron cloud mitigation through beam induced scrubbing Removal of limits of dumps and protection devices. All injectors: Main means to achieve the target HL-LHC proton beam parameters Beam Instrumentation

12 How LIU-injectors performances are presented Maximum intensity per bunch (RF) Present situation Achieved performance Collective effect in PSB/PS/SPS HL - LHC Non accessible beam parameters Line limits = preserve same beam quality as today

13 Standard scheme (72b trains) after LS1 Achieved HL-LHC

14 Standard scheme (72b trains) after LIU With Linac 4 after connection of Linac4 HL-LHC LIU upgrades SPS 200 MHz upgrade SPS e-cloud mitigation PSB-PS transfer at 2 GeV Limitations standard scheme SPS: longitudinal instabilities + beam loading PSB: brightness Performance reach 2.0x10 11 p/b in 1.9μm (@450GeV) 1.9x10 11 p/b in 2.3μm (in collision)

15 BCMS scheme (48 bunches / PS batch) LIU upgrades on top of the HL-LHC Linac4 connection SPS 200 MHz upgrade SPS e-cloud mitigation PSB-PS transfer at 2 GeV Limitations BCMS scheme SPS: longitudinal instabilities + beam loading PS: space charge SPS: space charge Performance reach 2.0x10 11 p/b in 1.37μm (@450GeV) 1.9x10 11 p/b in 1.65μm (in collision)

16 Timelines of the LIU project LIU (simulation, beam tests, equipment design, procurement) activities during Run 2 LIU installations and hardware works mainly during LS2 Beam commissioning of LIU beams Pb ion beams need to be ready by 2020 ion run Proton beams during Run 3 to be ready after LS3 2 Protons (E)YETS Ions Long Shutdown

17 The Linac4 Project Approved by CERN Council in June 2007, started on 1 January (as a first step towards the LHC Luminosity upgrade, integrated in LIU since 2011) Scope (from Project Plan, 2007): Build a 160 MeV H linear accelerator replacing Linac2 as injector to the PS Booster (PSB). The beam brightness out of the PSB is expected to increase by a factor of 2. Project Phases Design Construction Installation Commissioning Equipment building Access building Low-energy injector Linac4 tunnel Linac4-Linac2 transfer line ground level About 100m in length, connection to the PSB and option of a future extension to higher energy. Linac tunnel 12 m underground, surface building for RF and other equipment, access module at low energy.

18 Parameters and Layout Layout: Pre-injector (source, magnetic LEBT, 3 MeV RFQ, chopper line), 3 types of accelerating structures at 352 MHz (Drift-Tube Linac 50 MeV, Cell-Coupled Drift Tube Linac 102 MeV, Pi-Mode Structure 160 MeV), beam dump at linac end with switching magnet towards transfer line to PSB. Ion species H Output Energy 160 MeV corresponding to factor 2 in bg 2 w.r.t. 50 MeV of Linac2 double brightness Bunch Frequency MHz Max. Rep. Frequency 2 Hz Energy Length RF Power Focusing Max. Beam Pulse Length 0.4 ms [MeV] [m] [MW] Max. Beam Duty Cycle 0.08 % Chopper Beam-on Factor 65 % RFQ RF Chopping scheme: 222 transmitted /133 empty buckets Source current 80 ma DTL PMQs RFQ output current 70 ma CCDTL PMQ, 7 Linac pulse current 40 ma EMQs Tr. emittance (source) 0.25 p mm mrad Tr. emittance (linac exit) 0.4 p mm mrad PIMS EMQs Design Parameters from Linac4 Technical Design Report, 2006 PIMS CCDTL DTL chopper line RFQ ion source 160 MeV 103 MeV 50 MeV 3 MeV 76.4 m 18

19 Linac4 Status - building Installation in surface hall practically completed (17 klystrons, 12/14 modulators, power supplies, RF control, etc.)

20 Linac4 Status - tunnel Installed in accelerator tunnel: ion source, RFQ, DTL tank 1 (12 MeV), 5 CCDTL modules, main beam dump, part of transfer line. 12 MeV line (DTL1, RFQ, source) CCDTL (100 MeV) Main dump and bending to PSB

21 PSB Layout 4 sumperimposed synchrotrons

22 Objectives of the LIU-PSB Project - Goal: Produce higher brightness beams to match HL-LHC requirements - Should also allow higher beam intensities for non-lhc beams - Connection of the PSB with Linac 4 - Alleviate space charge effects at PSB injection - Increase injection energy from 50 MeV 160 MeV - Horizontal phase space painting - Longitudinal painting for very high intensity beams - New H - charge-exchange injection - Make production of beams with increased brightness possible - Drastically reduce losses at injection - 2 GeV Energy Upgrade of the PSB - Alleviate space charge effects at PS injection - Increase extraction energy from 1.4 GeV 2 GeV

23 1-s norm. emittance [mm mrad] Measured vs. Simulated Brightness Curves LHC25ns beam; constant bunch length over intensity range. H - injection to produce high brightness beams (not high intensity) See V. Forte presentation for PSB studies Present PSB performance for LHC beam production (measurements) y = x y = 0.005x PSB bunch intensity [E10] PSB performance with Linac4 for LHC beam production (simulations)

24 PSB Injection Line 24 Distributor to be replaced Vertical distribution septum to be replaced

25 25 LIU-PSB Activities Future PSB Injection Section

26 LIU-PSB Activities Finemet 5-cells open cavity Installation of 10 Finemet modules in PSB Ring 4: Beam accelerated up to 8e12 with Finemet Finemet on a cooling ring

27 Pick-up signal [a.u.] e-cloud signal [a.u. ] Magnetic Field T 1.4 GeV 26 GeV/c 2 nd injection h = 84 Low-energy BUs h = 7 Challenges Triple in splitting after the 2 PS and LIU solutions nd injection Split in four at flat top energy h = 21 High-energy BU Acceleration/Bunch splittings Longitudinal CBI new dedicated damper Transient beam loading/cbi 10 MHz FB amplifiers 10/40/80 MHz cavity impedance 1 turn delay FB Each bunch from the Booster divided by = 72 Transition crossing no limitation expected B T Flat top: Intensity Longitudinal CBI new damper h=21 h=42 h= Electron cloud 0.9 transverse FB Transverse instabilities transverse FB 0.6 h= Intensity Av. intensity = 1.33*10 11 ppb 0.3 1st Injection 2nd Injection time [us] Time ms Injection flat bottom: Space charge higher 2 GeV brightness injection upgrade with 2 GeV Headtail instability transverse FB time [us] 27

28 Space Charge at injection (1.4 GeV - 2 GeV) Study to determine largest acceptable tune spread. Today max acceptable: ΔQy ~ 1.4 GeV HL-LHC max needed: ΔQy > 2 GeV Goal: demonstrate that possible to inject a beam with ΔQ> 0.3 with limited emittance blowup (max 5%) Experimental studies: Learn from operational beams experience. Current Laslett at about with Qy<0.25 Tune scan to identify via beam losses dangerous resonances Driving terms measurements Compensate resonances (as done already in 1975 with injection at 50 MeV) Simulation studies: PTC Orbit(pyOrbit) simulations IMPACT MADX-FZM simulations Lack of good magnetic error model No error tables from magnetic measurements (à la LHC) available from important results: - Better understanding of integer resonance - Better understanding of 4 th (or 8 th ) order resonance Opera -based magnetic error simulations

29 Vertical Emittance Growth Losses [%] Space charge issue: Vertical growth vs. Tune-spread vs. Losses 1.5 Vertical Emittance Growth vs. Tune Shift See Raymond s presentation Working Point (6.23 ; 6.245) Working Point (6.23 ; 6.255) Existing operational LHC-type beams Sometimes 4 th order res. used to scrape tails Vertical Incoherent Tune shift 0

30 Current activities - Improve understanding of existing space charge limits - Integer resonance (in collaboration with LBL) - 4 th order resonance (in collaboration with RAL, talks of Raymond) - Normal 3 rd order resonance (in collaboration with GSI, talks of Alexander and Giuliano) - Understand indirect space charge effects (talk of Alexander) - Improve machine modeling - Random multipoles errors from geometry - Machine alignment - Longitudinal and transverse impedance model - Still missing : chromo-geometric terms modeling - Investigate alternative solution to increase maximum acceptable direct tune shift on top of the 2 GeV injection energy upgrade (baseline) - Hollow bunches in the longitudinal plane - Horizontal dispersion increase - Resonance compensation - Fully coupled optics : generate vertical dispersion by linear coupling

31 Longitudinal Coupled bunch instabilities Longitudinal CB instabilities appear after transition driven by 10 MHz cavity impedance With new dedicated longitudinal damper possible to reach more than 2.5e11 p/b at extraction Wide-band Finemet cavity (0.4 >5.5 MHz, V RF = 5 kv) Installed during LS1 Spectrum of beam induced voltage in Finemet cav. With and without beam loading compensation 31

32 Introduction SPS cycle for LHC beam SPS budget for total losses: 10% - Losses at start of acceleration ~5% (nominal intensities ) - Transverse scraping at flat top ~3% SPS budget for emitt. growth: 10% Preserve high brightness along 11 s long flat bottom e-cloud longitudinal multi-bunch instability

33 SPS space charge Measurements in 2012/13 showed that injecting a beam with an estimated DQ=0.21 can be tolerated on the SPS flat bottom within <10% emittance growth and losses (i.e. the SPS budget) Q: Can we reproduce this behaviour in simulations?

34 Introduction: nominal and higher intensities beams V 200 MHz MD end poor lifetime - horizontal instability - transv. emit. blow-up N~1.2x10 11 p/b τ avg =1.47 ns N~1.35x10 11 p/b τ avg =1.63 ns losses and bunch length increase for higher intensities

35 SPS limitations: beam loading & instability 200 MHz voltage as a function of RF current now and after RF upgrade MHz RF upgrade: - rearrange existing 4 cavities to 6 shorter cavities - add 2 new power plants (1.6 MW) - pulsing mode (f rev ) - new cavity and beam control nominal beam: I b =1.4 A HL-LHC After RF upgrade: significant increase in voltage (plus 20 % impedance reduction) voltage at flat top could be still not sufficient for HL-LHC intensity due to beam induced voltage ~ ImZ/n and emittance blow-up (long. instability)

36 SPS limitations: longitudinal multi-bunch instability Longitudinal multi-bunch instability with very low threshold: 4x10 10 p/b (needed for nominal beam > 1.2x10 11 p/p) single RF Present cures used in operation: (1) 800 MHz (4 th harmonic) RF system in bunch-shortening mode with V 800 = V 200 /10 during the whole cycle phase control issue due to beam loading double RF N~1.2x10 11 p/b (2) Controlled longitudinal emittance blow-up by band-limited phase noise during ramp issues due to bunch-by-bunch phase variation

37 Longitudinal impedance reduction needed Impedance reduction (vacuum flanges) July Increase in instability threshold without vacuum flanges (~2) HL-LHC target intensity can be achieved - Beam measurements and simulations cross-checking - Design of shielding (factor 6-8 reduction) and of new flanges - Total number of flanges 529, ~10 types See A. Lasheen presentation shields 1 RF 12 bunches 9x10 10 p/b Longitudinal multi-bunch instability during ramp: agreement between measurements and simulations for 12 b in 1 RF

38 SPS limitations: e-cloud Nominal LHC beam recovered after LS1 (end 2014) High intensity (1.9x10 11 p/b) 25 ns beam at 26 GeV/c: - poor lifetime - horizontal instability - transverse emittance blow-up (> factor 4) H V

39 Ions Pb ions to the collider

40 LIU-IONS target: 7x nominal peak luminosity Achieved in 2011 L peak 5x10 26 Hz/cm 2 Beam energy 3.5 Z TeV LIU-IONS 7x10 27 Hz/cm 2 7 Z TeV Intra Beam Scattering & space-charge already at the limit on SPS flat bottom We need to pack a larger number of bunches in LHC

41 Scheme in 2011 (2013 performance) 200ns 200ns 200ns 200ns max. 7 injections Twice 5.5x10 8 ions/bunch 3.8x10 8 ions 2.2x10 8 ions 1.6x10 8 ions 1.4x10 8 ions max. L E I R P S S P S L H Post-LS2 Scheme 100ns 200ns 100ns max max. 13 injections Twice 8x10 8 ions/bunch 5.6x10 8 ions before splitting 2.8x10 8 ions ~2μs 50ns spacing ions in collision 50ns spacing

42 How to increase Luminosity after LS2? Linac3 & Source: Increase Intensity : Low energy beam transport (LEBT) Injection spacing: 200ms 100ms LEIR: Injected int. x 2: Injection rate in LEIR from 5Hz to 10Hz Extracted int. x 1.45: LEIR low energy beam loss mitigation PS: Numb. of bunches x 2: bunch splitting 4 bunches out of PS with 100ns bunch spacing SPS: New SPS injection system: 100ns bunch spacing SPS slip-stacking 50ns bunch spacing into LHC

43 BHN current [100A] Main scheme limitation: LEIR maximum intensity LEIR maximum extracted intesity limited to ~ charges probably due to: 1. Working point too close to 4 th order resonance (space charge) 2. Transverse instability at RF capture 3. Positive chromaticity in the vertical plane 4. Beam loss associated to RF-capture rather than mag. Ramp

44 Design tune: Q H =1.82, Q V =2.72 Q x - Q y = -1 2Q x - Q y = 1 4Q y = 11 Q x + 3Q y = 10 3Q y = 8 2Q x + 2Q y = 9

45 LEIR Instability at RF capture and magnetic ramp Pickups output: Before: -20ms 1815ms Beam loss starts here After: +20ms Beam loss continues

46 Conclusions - LIU targets 2019 for the implementation of the different upgrades in proton and ion injector chain. - Four new machines (L4 PSB@2 GeV, PS@2 GeV, SPS 200 MHz) will have to be commissioned in parallel in Space charge studies are progressing very well - Invaluable support from the community brought important results