Heavy Ion Beams in the CERN LHC Present plans and beyond

1. Heavy Ion Beams in the CERN LHCPresent plans and beyond John Jowett CERN Thanks to several colleagues, especially Django Manglunki for injector material

2. Plan of talk • Part I – “official” status and plans for LHC HI • LHC as heavy-ion collider • Pb-Pbcollisions so far • p-Pb run in 2012 • Plan for the LHC heavy-ion programme until Long Shutdown in 2023 (LS3) • Part II – unofficial and personal views • Heavy ions in the HL-LHC period • Performance limits and prospects • Options for colliding species • LHeCand HE-LHC

3. Part I status and plans for LHC Heavy IONS

4. LHC Ion Injector Chain ECR ion source Provide highest possible intensity of Pb29+ RFQ + Linac 3 Adapt to LEIR injection energy strip to Pb54+ LEIR Accumulate and cool Linac3 beam Prepare bunch structure for PS PS Define LHC bunch structure Strip to Pb82+ SPS Define filling scheme of LHC

5. Luminosity of a hadron collider Parameters in luminosity Revolution frequency Number of particles per bunch b Number of bunches per beamkb Number of bunches colliding kc< kb Relativistic factor  Normalised emittance n Beta function at the IP  * Crossing angle factor F Full crossing angle c Bunch length z Transverse beam size at the IP * (Heavy-ion colliders (eg, p-A) may need slightly more general formula.)

6. Luminosity factors: bunch intensity Nb • Limited mainly by injectors • Source intensity, space-charge effects in various machines, intra-beam scattering (IBS) in SPS, RF noise in SPS, … • At present we get higher Nb(and L) for Pb with larger bunch spacing (200 ns vs 100 ns) • In LHC • IBS worse (especially at injection) • Limit on total intensity (kb Nb) from collimation losses

7. Luminosity factors: emittanceεn • Given initially by injectors • Space-charge effects in various machines, intra-beam scattering (IBS) in SPS, RF noise … • Increases by IBS at LHC injection • Spread in values along bunch train • May be other effects in p-A • Increases more slowly by IBS in physics

8. Luminosity factors: no. of bunches colliding kc • Limited by minimum bunch spacing (100 ns) from injectors • RF frequencies of injectors, bunch splitting in PS, kicker rise times, … • For Pb-Pb at least, 200 ns presently better • Details of bunch filling pattern can give some differences in kc between experiments

9. Luminosity factors: collision optics β* • Limited by aperture in final focus triplet • Better with increasing energy • Number of IPs with small β* • Increases luminosity burn-off of intensity • Global chromatic effects • Generally means that HI runs push optics further

10. Luminosity factors: beam energy γ • Beam energy will increase to ~6.5-7 Z TeV in 2015 • Reduced geometrical beam sizes • Allows smaller β* • Reduced IBS, increased synchrotron radiation damping • Greater energy deposition by lost particles • Magnets have greater propensity to quench • BFPP and EMD from collisions • Collimation losses

11. Luminosity decay When luminosity/bunch is high, the luminosity falls rapidly. Luminosity may also decay for other reasons (IBS emittance blow-up and losses).

12. Main and secondary Pb beams from ALICE IP Optimal position for Pb-Pb Considered for installlation in LS2. May also need horizontal crossing angle components in ALICE New collimators around experiments to intercept secondary beams from IPs for Pb-Pbcollisions(different locations optimal for p-p luminosity debris).

13. Losses during Pb-Pb Collisions in 2011 Bound-free pair production secondary beams from IPs Losses from collimation inefficiency, nuclear processes in primary collimators IBS & Electromagnetic dissociation at IPs, taken up by momentum collimators ?? But we have learned a lot from the 2011 run … …despite no dedicated MD time for Pb-Pb. See also M. Brugger’s backup slides

14. 2012 update of Particle Data Group collider parameters now has a whole page for heavy ions.

15. Pb-Pb Parameters in 2011 vs. Design

16. Ion Injector Chain Performance 2011 Wed 7 Dec 2011 07:44:32 200 ns created in 2 bunch PS batches, sustained in 24 bunch SPS batches thanks to shortened SPS injection kicker rise time (E. Carlier) Uneven intensity (and emittance) along batches due to IBS (etc …) on long injection porches in SPS and LHC.

17. Beam parameter evolution, 2011 run M. Schaumann

18. Luminosity evolution: Nominal scheme, full energy Particles per bunch Transverse emittance An “ideal” fill, starting from design parameters. Luminosity burn-off, IBS, radiation damping, RF noise, beam-gas,multiple scattering, etc. Increasing number of experiments reduces beam and luminosity lifetime. Higher Nb makes this worse! Luminosity

19. Luminosity evolution in Pbluminosity upgrade Particles per bunch Transverse emittance RF noise used to control transverse IBS Emittance control is key, RF noise goes some way towards transverse cooling. More bunches is another route. (Don’t know how to do this yet!). An “ideal” fill, starting from parameters giving 5×nominal luminosity. Luminosity

20. Possible route to 50ns for HL Pb-Pb • Design current from Linac 3 (~50mA) • LEIR • Produce 2 bunches of ~109 Pb54+ in same emittance (i.e. twice today) • PS gymnastics • Batch compression to 100ns h = 16 -> 18 -> 21(no need for new cavities, 10MHz system exists) • Splitting h = 21 -> 42 (20MHz system exists but VRF acceptance to be checked) • 4 bunches > 1.4 x108 Pb82+ into SPS • 12 SPS injections spaced by 50ns • Similar bunch quality as present beam • 48 bunches of ~1.4x108 Pb82+ • Transverse emittances ~0.85mm • But with 50ns spacing and hopefully less spread in bunch population • Note: longer LHC injection time

21. p-Pb feasibility test, Part 1, 16h on 31/10/2011 • Almost unprecedented mode of collider operation • See pA@LHC workshop • Several hours setup of first Pb beam of the year (timing, many details…) • Stored 4 Pb bunches in presence of 304 p bunches (~10% nominal intensity) at injection • Lifetime no worse for presence of p bunches • Emittance blow-up, does not appear to be worse than for Pb alone • Dumped and re-injected 4 fresh Pb • Still OK • Ramped 2 Pb and 2 p bunches, good lifetime • Re-phased RF (cogging) to move bunches 1 encounter point 9 km back to ATLAS, no losses

22. Injection and ramp of 2 Pb with 2 proton bunches

23. Target p-Pb performance in 2012 (ATLAS/CMS) Integrated luminosity by scaling from 2011 (c.f. ~7 pb-1 NN in Pb-Pb)Average Pb bunch intensities from best 2011 experience.Proton bunch intensities conservative, another factor 10 ???Proton emittance conservative, another factor 1.37 ?Untested moving encounter effects, possible reduction factor 0.1 ??

24. Choice of operating energy for p-Pb 2.2 ZTeV “ideal” but would cost factor ~6-7 in integrated luminosity and exceeds 1 mm orbit limit in LHC arcs. 4 ZTeV, the final choice for 2012, will be “easiest” from accelerator point of view – calibration data for 2015 Pb-Pb.

25. LHC Heavy Ion programme until 2022 - status • An implementation of the approved physics programme consistent with plans for the CERN accelerator complex in coming decade • Agreed during 2011 • Takes account of p-p operation, shutdowns, SPS HI programme, etc. • Updated at LHC Chamonix Workshop, Feb 2012, incorporating new knowledge from the 2011 Pb-Pb run • Some flexibility still available • In a typical running year of LHC, a heavy-ion run will take place in the ~4 weeks before the end-of-year stop/shutdown.

26. LHC Heavy-Ion Programme to 2022

27. Relation to SPS fixed target programme

28. Nucleus-nucleus programme status • In ~8 weeks total Pb-Pb operation in 2010-11, the LHC has attained • Twice design Pb-Pb luminosity at half-design energy (scaling with E2). • ~16% of the integrated luminosity goal (1 nb-1) for the present phase of Pb-Pb. • Pb-Pb in 2012 might give ~250 μb-1 • Decision to go for p-Pb instead • Otherwise no p-Pb before 2016 or 2017 • But this is a new, more complex and almost unprecedented mode of collider operation

29. Part I - Conclusions • 2011 results encouraging for future performance • Quench limits, strategies to help avoid them • Still many uncertainties • Still “only” design intensity in 100 ns Nominal injection scheme • We do not yet have a clear path beyond about twice design luminosity • DS collimator installation for ALICE in LS2 • Looking for solutions for more bunches in injectors

30. Part II PERSONAL VIEWS on FUTURE BEYOND 2022

31. Heavy ions with High-Luminosity LHC • CERN planning foresees HL-LHC upgrade, running p-p after LS3, from 2023 onwards • Major resources committed now • Case to be made for devoting part of LHC time (1 month/year?) to running heavy ions in this period, to maintain and upgrade heavy ion capabilities of the CERN complex • No resources for further upgrade studies at present • What are the possibilities ?

32. Possible beams (1) • Pb • Known limits, not obvious how to go beyond • Luminosity lifetime vs no. of experiments • Stochastic cooling ? • M. Blaskiewicz, IPAC 2011 • Major investment, some R&D • Compensate IBS at injection – not a huge gain • Probably difficult during physics (cf RHIC) • Other cooling methods ? • Coherent electron cooling (Litvinenko) – not demonstrated so far, R&D • Lighter ions, Ar, Xe, … • Various possibilities from present source • New source (+linac??) for LEIR medical • He to Ne

33. Possible beams (2) • Hybrid combinations p-A, A1-A2, etc. • Review potential after experience of p-Pb in 2012 • Deuterons (next slide) • No studies for now – several years lead time required • Uranium ? • Regulatory concerns, major upgrade of source area, feasibility unknown • No studies so far • Several years lead time certainly necessary

34. Deuterons in LHC (D-A,p-D) collisions • No deuteron beams in present CERN complex • Linac4 cannot accelerate D, even with a D- source • Linac2 should be shut down, eventually • Only possibility with existing accelerators is to use present heavy ion Linac3 • Requires new D source, RFQ, switchyard, • Several years’ lead time to develop • Uncertain how LEIR would perform with D • Present studies of new light ion source (He to Ne) under way (medical use of LEIR), might be extended to D if officially requested (presently no formal request for LHC) • Possible alternative (D. Kuchler): cyclotron injecting ~1 mA D directly to PS synchrotron • Could be cheaper, even table-top if injecting to LEIR

35. D-A performance • Very rough for now … help from D. Kuchler • However, this gives a big margin in fields and there are no losses from stripping. • If source is intense enough and losses in Linac can be tolerated, can hope for 200-500 µA at end of linac (with somewhat degraded beam quality). • Take safety reduction factor 5 for unknowns in PS, SPS, etc. • D-A luminosities few times smaller than p-A

36. LHeC • Proposal for e-p, e-D, e-A using LHC beams colliding with new electron accelerator • Recently published CDR • Reflects substantial informal effort over several years • Very large energy recovery linac complex to be built • New accelerator technology • Small demonstration machine first • Proposed schedule • Assumes new experiment in IR2 • Construction and installation within constraints of LHC operation and shutdowns

37. From LHeC CDR, Section 7.13.1 • In order to avoid interference with the high luminosity proton-proton operation, this mode of operation would naturally be included in the annually-scheduled ion operation period of the LHC. • In principle, the CERN complex could provide A-A (or even p-A) collisions to the LHC experiments while the LHeCoperates with e-A collisions. • (Note that e-Pb integrated luminosity could be higher in dedicated e-Pb mode (reduced luminosity burn-off).

38. Luminosity estimate for e-Pb, e-D in Linac-Ring Assumes nominal Pb beam circulating in LHC. N.B. these are electron-nucleon luminosities (208 times the electron-nucleus luminosity for e-Pb).

39. Heavy ions at HE-LHC ? • An increase in LHC energy by a factor ~2 • Dramatic increase in synchrotron radiation damping of ion beams, IBS weaker also ~ free cooling system! • Could see luminosity increasing at start of fills. • (Recall that Pb nuclei damp twice as fast as protons.) • Potential for very high Heavy Ion luminosity as well as energy • Needs study!

40. Part II - Conclusions • LHC has considerable further potential for various A-A and p-A beyond 2022 • R&D and preparation not yet foreseen • Special-energy p-p, p-A calibration runs? • Some difficult choices and principles to clarify • LHC programme needs to foresee running time • Continued development of LHC ion injectors • R&D for possible LHC upgrades