Lead Ions in the LHC

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1 Lead Ions in the LHC Contributors to this talk (re-run run of Chamonix plus some extras): H. Braun, J.M. Jowett, E. Mahner, K. Schindl, E. Shaposhnikova (CERN) M. Gresham (Reed College, Portland), I. Pschenichnov (INR, Moscow) Thanks to: many other CERN colleagues, I. Baishev,, S. Striganov (FNAL) J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 1

2 Ions for LHC (I-LHC) Project New I-LHC I Project Web pages: Members of the I-LHC I Steering Group: Karlheinz Schindl : Chairman Hans Braun : Ion collimation in LHC Christian Carli : Scientific Secretary Michel Chanel : Deputy Chairman, LEIR Steven Hancock : RF aspects in LEIR and PS Charles Hill : Linac 3, ECR ion source John Jowett : LHC, linkman to experiments Django Manglunki : SPS, operational aspects Michel Martini : PS, line to SPS Stephan Maury : Linkman to AC Flemming Pedersen : Low level RF all machines Elena Shaposhnikova: RF aspects SPS and LHC J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4

3 Plan of talk The I-LHC I Project Review new ion parameters Small-angle angle separation scheme Quench limit and ECPP Collimation Vacuum Aspects Luminosity and beam lifetime Conclusions, implications J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 3

4 Parameters for Lead Ions in LHC Revision/verification of all parameters Started at Chamonix Workshop 3 Summarised in LHC Design Report Vol I, Chapter 1 Recent changes: Introduction of Early Ion Scheme Optics update, small-angle angle crossing scheme for ALICE Revised lifetimes, IBS, etc. No MHz RF system for capture at injection now J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 4

5 Nominal scheme parameters J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 5

6 Nominal scheme, lifetime parameters J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 6

7 Early scheme Parameters Only show parameters that are different from nominal scheme J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 7

8 Some things are straightforward Beam current and stored energy 1 times lower Many limits to performance of proton beams are not a problem for lead ion beams impedance-driven driven collective effects beam-beam electron cloud (?) activation and maintenance of collimators Same geometrical transverse beam size and emittance some aspects are similar Optics, dynamic aperture, mechanical acceptance, etc. more or less carry over from protons. J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 8

9 Optics Ion optics at injection/ramp assumed to be essentially same as protons Lead ion optics in collision Update for move of Q3 magnets (part of V6.5) Focus on IR (ALICE, specialised ion experiment) Maintain β*=.5 m (unlike protons which have β*=.55 m for reasons of aperture) Ion collisions for ATLAS/CMS may use proton optics Or also squeeze further Main issue is separation J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 9

10 .1 Separation in IR: three illustrative cases y c êm sêm y c êm sêm f IPbump = 17%, f ALICE = 1%, q c = 8. mrad f IPbump =-65%, f ALICE =-1%, q c = 81. mrad Two ways of getting a crossing angle of 8 µrad; one way to get zero crossing angle. Beam 1 / Beam y c êm f IPbump = 4%, f ALICE = 1%, q c = -.8 mrad J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 1 sêm Total separation is superposition of ALICE spectrometer bump and external vertical separation Animation!

11 Yês y Parasitic beam-beam encounters Bad! sêm Yês y sêm f IPbump = 17%, f ALICE = 1%, q c = 8. mrad f IPbump =-65%, f ALICE =-1%, q c = 81. mrad Show only vertical separation in units of vertical RMS beam size of Beam 1. Red lines are possible (ion) encounters (S b /) Yês y f IPbump = 4%, f ALICE = 1%, q c = -.8 mrad J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 1 sêm Zero crossing angle is just about achievable with minimum 3σ separation (strictly need µrad).

12 Aperture (APL program) All meet the canonical aperture requirements with β*=.5m J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 13

13 Electromagnetic Interactions of Lead ions QED effects in the peripheral collisions of heavy ions Rutherford scattering: Free pair production: Electron capture by pair production (ECPP) 8 Pb Pb 8+ γ 8 Pb Pb 8+ Copious but harmless γ Copious but harmless Pb + Pb Pb + Pb + e + e γ Pb Pb + Pb + e 8 Pb Electron can be captured to a number of bound states, not only 1s. Secondary beam out of IP, effectively off-momentum 1 δ p = =.1 for Pb Z 1 Electromagnetic Dissociation (EMD) 8 Pb Pb 8 + γ 8 Pb 8+ + ( 8 7 Pb Pb ) * + n Secondary beam out of IP, effectively off-momentum: δ p 1 3 = = A 1 for Pb (Numerous other changes of ion charge and mass state happen at smaller rates.) J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 14

14 Nuclear cross sections 4 Cross-section section for Pb totally dominated by electromagnetic processes Values for non-pb ions may need upward revision? sêbarn s tot s ECPP s EMD s H H ECPP ECPP values values from from Meier Meier et et al, al, Phys. Phys. Rev. Rev. A, A, 63, 63, (1), (1), calculation calculation for for Pb-Pb Pb-Pb at at LHC LHC energy energy Total cross - section for ion removal from beam Kr In Pb σtot = σh + σemd + σecpp Ar O He sh semd secpp stot Hydrogen µ Helium µ Oxygen Argon Krypton Indium Lead J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 15

15 Cross-section section for ECPP Involved topic, topic, numerous references Extrapolation from from SPS SPS measurements at at lower lower energy energy in in Grafström et et al, al, PAC99 PAC99 Electron can be be captured to to a number of of bound states, not only 1s. Meier et et al, al, Phys. Rev. A, A, 63, 3713 (1), calculation for for Pb-Pb at at LHC energy J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 16

Cross-section section for ECPP Use Meier et al s result for Pb-Pb at LHC energy: σ ECPP = [ σ (1s ) + σ (s) + σ (3s) + L] + σ ECPP ECPP ( p 1/ ECPP ) + σ ECPP [ 5. + 8.8 + 8. + L] ( p ECPP 3 / + 9.

16 Cross-section section for ECPP Use Meier et al s result for Pb-Pb at LHC energy: σ ECPP = [ σ (1s ) + σ (s) + σ (3s) + L] + σ ECPP ECPP ( p 1/ ECPP ) + σ ECPP [ L] ( p ECPP 3 / L barn ) + L σ ECPP ( ns) σ (1s ) n ECPP 3 [ ζ(3) σ (1s )] ECPP 81barn L barn C.f. 4 barn used in previous discussions J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 17

17 Main and ECPP secondary beams 5σ beam envelopes, emerging to right of IP sêm xêm yêm -. Beam screen -.3 Collimation of secondary beam seems difficult. Uncorrected strong chromatic effects of low-b insertion cannot use linear beam sizes for Pb 71+ beam J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 18

18 Quench limit (conservative) is Dilution over.8.6 l d 1m, Secondary beam spot 8 1 In quadrature with shower length 1m 4 Pb/m/s 1.4 m Beam screen in a dispersion suppressor xêm dipole x / m y / m yêm s / m Plan to improve heat deposition estimate with FLUKA calculations. 371 sêm Energy deposition by ion flux from ECPP exceeds nominal quench limit of superconducting magnets by factor at nominal luminosity. DIRECT LIMIT ON LUMINOSITY. J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 19

19 Collimation for Pb ions 8 Pb 8+ ion ion-graphite interactions compared with p-p graphite interactions. From Hans Braun J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4

20 Robustness of collimator against mishaps FLUKA calculations from Vasilis Vlachoudis for dump kicker single module prefire The higher Ionisation loss makes the energy deposition at the impact side almost equal to proton case, despite 1 times less beam power. Similar damage potential. From Hans Braun J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 1

21 Cleaning efficiency The probability to convert a 8 Pb nucleus into a neighboring nucleus. Impact on graphite at LHC collision energy. From Hans Braun J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4

22 Simulation of collimation (Hans Braun) Model of ion fragmentation, linear optics, collimators and beam aperture Suppose beam lifetime is down to 1 min due to non-luminosity processes, e.g., IBS, beam-gas, resonances, Collimators tend to put ion fragments on trajectories with large momentum errors and small betatron amplitude but the secondary collimators are designed to cut betatron amplitudes Acts like one-stage system Worrying results at collision energy (following slides) Various hot-spots around ring Seems OK at injection energy J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 3

23 P ' (W/m) Fractional heat load in dispersion suppressor, τ=1min Nominal ILHC beam at collision Maximum for continous loss, corresponds to local collimation inefficiency of m -1 Pb 8 Pb 7 Pb 6 Pb 5 Pb 4 Pb 3 Tl 4 Tl 3 Tl Tl 1 Tl Tl 199 Tl 198 Hg 1 Hg Hg 199 MQ.1R7.B1 MQTLI.1R7.B1 MB.A11R7.B1 MB.B11R7.B1 MQ.11R7.B1 MQTLI.11R7.B distance from TCP.D6L7.B1 (m) From Hans Braun J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 4

24 Nominal ILHC beam at collision 15 Collimator load distribution Loss map 1 P ' (W/m) PCOLL (W) TCP.6L3.B1 TCS.5L3.B1 TCS.A4R3.B1 TCS.B4R3.B1 TCS.A5R3.B1 TCS.B5R3.B1 TCS.C5R3.B1 TCP.D6L7.B1 TCP.C6L7.B1 TCP.B6L7.B1 TCP.A6L7.B1 TCS.C6L7.B1 TCS.B6L7.B1 TCS.A6L7.B1 TCS.B5L7.B1 TCS.A5L7.B1 TCS.B4L7.B1 TCS.A4L7.B1 TCS.A4R7.B1 TCS.B4R7.B1 TCS.C4R7.B1 TCS.D4R7.B1 TCS.E4R7.B1 TCS.F4R7.B1 TCS.G4R7.B1 TCS.A5R7.B1 TCS.B5R7.B1 IP1 IP IP3 IP4 IP5 IP6 IP7 IP8 IP Distance from IP1 (km) 6 x 14 4 Time development after first impact on collimator particles lost on collimators particles lost elsewhere particles in beam N TURN J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 5

25 Interaction of Pb ions with residual gas Losses due to nuclear scattering on residual gases Atoms in residual gases (6 usual suspects in Design Report for protons) have Z 8. For simplicity, discuss only the dominant inelastic nuclear scattering (leave out elastic and electromagnetic contributions, EMD, ECPP which are smaller). Somewhat optimistic! Dominant beam-gas lifetime: 1 = is independent of intensity c σ i i τ n bg i gases Multiple Coulomb scattering on residual gas also causes emittance growth (similar to protons, not treated here). kbibe Pbg = Lost ions are a heat load: Zec τ bg J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 6

26 Inelastic nuclear cross sections Cross-sections sections of proton-nucleus nucleus and nucleus-nucleus inelastic interactions at ~1 GeV/n, assumed similar at.75 TeV/n (as is the case for protons) Simple formula, V.S. Barashenkov, 1993 pa : A A 1 σ : in where σ ( Z, A) σ in ( Z, A, Z, A ) 1 = σ 1 A =.38 barn. Comparison with earlier Hard-sphere overlap model (Bradt & Peters 195) 1/ 3 1/ A A = σ A σ êbarn / / 3 + A / 3 Z A A 1 ( A A ) 1 1/ / 3 A 1/ 3 Z A 1 1 Z A Pb, Barashenkov Pb, Hard-sphere pa, Hard-sphere pa, Barashenkov J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 7 Z

27 Protons with lifetime 1h Required gas pressures Gas σ in nêm 3 PH3KLênTorr PH5KLêPa P bg êhwêml H He CH HO CO CO Lead ions with lifetime 1h Lead ions with pressure that gave proton lifetime 1h Gas σ in nêm 3 τ bg êh P bg êhwêml H He CH HO CO CO Gas σ in nêm 3 PH3KLênTorr PH5KLêPa P bg êhwêml H He CH HO CO CO J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 8

28 Heavy-ion induced desorption data: New Overview Au η eff [molecules/ion] Pb 7+ Zn 1+ Au 31+ Pb 53+ U 8+ BNL (AGS) BNL (RHIC) CERN (LINAC 3) CERN (SPS) GSI (HLI) GSI (HLI) GSI (SIS 18) In 49+ PRELIMINARY Ion energy [MeV/u] J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9// From Edgar Mahner

29 Electron Cloud effect with ions? Key parameters are charge/bunch and bunch spacing We do not expect electron cloud effects with Pb ions. 1 µ 1 11 N b Q ion LHC p nominal 8 µ µ µ 1 1 µ 1 1 Pb early RHIC with ecloud Pb nominal LHC p no electron cloud (FZ simulation) êS b J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 3

30 Longitudinal parameters Longitudinal emittance at injection from SPS has been reduced since we no longer have MHz RF system for capture. J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 31

31 Intra-beam scattering Injection Collision J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 3

32 Scaling with respect to protons in same ring, same magnetic field Synchrotron Radiation t p ÅÅÅÅÅÅÅÅÅÅÅ t ion Radiation damping for Pb is twice as fast as for protons Many very soft photons Critical energy in visible spectrum Radiation damping enhancement for all stable isotopes Z Lead is (almost) best, deuteron is worst. J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 33

33 J I I 8 ( δ ) s π, ρ d logu = dδ I Damping partition number variation Variation of longitudinaldampingpartition number wit h momentumdeviation of ε = ( δ ) I ( K () s D () s ) ds 1 4 x s 1 s 3 I + I, 4 I + I 8 δ s, δ s 1 f = η f RF RF Dampingrate α x for horizontalbetatron motion ( δ ) = J ( δ ) α ( ) = ( 3 J ( δ )) α ( ) s x s x ε s x closedorbit: Allows us to switch some radiation damping from longitudinal into horizontal motion Heavily used at LEP, PETRA, TRISTAN, Overcome IBS, shrinking horizontal emittance to maximise integrated luminosity Price of a few mm negative closed orbit in arc QFs needs further study J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 34

34 Luminosity and beam lifetime Initial beam (intensity) lifetime due to beam-beam interactions (non-exponential decay) τ NL = kbnb n L σ exp tot =.4 hour for nominal L = 1 cm s with Pb - Pb n exp where n exp is the number of experiments illuminated But luminosity may be limited by experiment or quench limit b kbn f L = 4πσ * b kbn f = 4πβ * ε n can have same luminosity by varyingβ* N γ β*-tuning during collision to maximise integrated luminosity especially if N b can be increased. b J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 35

35 Nominal scheme, lifetime parameters (again) J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 36

36 cm - s 1-1 L/cm Operational parameter space with lead ions ECPP Quench limit Nominal Visible on BCTDC Visible on BCTDC Early Visibility threshold on FBCT Visibility threshold on arc BPM Nominal single bunch current b µ I b /µa Thresholds for visibility on BPMs and BCTs. J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 37

37 Conclusions Operation of LHC with lead ions limited by diverse effects, often qualitatively different from protons ECPP leading to magnet quench limits luminosity Poor collimation efficiency, large particle losses in dispersion compressor, limit on total current Either keep > 4 min lifetime for nominal Ion parameters in collision (!) or reduce beam current Early scheme will allow relatively safe commissioning, access good initial physics Reduced risk of magnet quenches from ECPP Reduced heat deposition related to collimation But Pb ions require much lower vacuum pressure than protons Independent of beam intensity! Restricted to a small range of operational parameters below the nominal luminosity Do everything possible to expand it! J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 38

38 Implications Some effects (collimation, ) limit total beam current but there are no hard limits on single bunch current More luminosity by distributing current in fewer bunches Optimum filling scheme may be somewhere between Early (kb=6) and Nominal (kb=59) Possibility of running with, e.g,, 1-3 bunches should be kept in mind by injectors, all LHC systems and the experiments. Do everything possible to increase single-bunch current Push all limits in injector chain Many uncertainties to be resolved with further work ECPP heating, EMD losses, vacuum, collimation, RF noise, J.M. Jowett, LHC Experiment Accelerator Data Exchange Working Group, 9//4 39

(Lead) Ions in the LHC

(Lead) Ions in the LHC Large Hadrons in the Large Hadron Collider John Jowett BE-ABP J.M. Jowett, LHC Performance Workshop, Chamonix, 6/2/2009 1 Plan of talk n Simplified survey of parameter space Energy,