Frank Zimmermann LHC-CC’10, Geneva, 16 December 2010

1. Other Crab Cavity Applications - LHC, RR-LHeC, RL-LHeC, HE-LHC, p-driven plasma accelerators … Frank Zimmermann LHC-CC’10, Geneva, 16 December 2010

2. outline • crabbing of colliding beams at the IP - improving geometric overlap - boosting beam-beam tune shift - luminosity leveling - avoiding off-center collisions from beam loading → HL-LHC, RR LHeC, RL LHeC, HE-LHC, eRHIC,… • off-momentum cleaning → HL-LHC • bunch compression → PDPWA

3. applications of crab cavities • crabbing of colliding beams at the IP - improving geometric overlap - boosting beam-beam tune shift - luminosity leveling • - avoiding off-center collisions from beam loading • off-momentum cleaning • bunch compression

4. improving geometric overlap primary motivation for HL-LHC & LHeC “Piwinski angle” “luminosity reduction factor” without crab cavity qc/2 nominalLHC effective beam size: s*x,eff≈ sx*/Rf “LPA” upgrade crab cavities make Rf~1 “FCC” upgrade

5. improving overlap with crab cavities at LHeC? - several options RR LHeC: new ring in LHC tunnel, with bypasses around experiments RR LHeC e-/e+ injector 10 GeV LR LHeC: recirculating linac with energy recovery, or straight linac

6. LHeC – general parameters • $smaller LR p-b* value than for • nominal LHC (0.55 m): • reduced l* (23 → 10 m) • only one p beam squeezed • new IR quads as for HL-LHC B. Holzer, M. Klein, F. Zimmermann Baseline without crab cavities With crab cavities (less SR!): RL crossing angle ~8 mrad

7. LR-LHeC crossing angle • need to separate e/p beams by 6-9 cm at 10 m from IP (i.e. angle of 6-9 mrad) [constraint from magnet design] • w/o IR-dipoles, crab cavities need 20-30x HL-LHC crab voltage, or ~200 MV ! • maximum allowed crossing angle for luminosity w/o crab crossing is < 0.5 mrad (see graph) with

8. crab cavities helpful for all future lepton-hadron colliders V. Litvinenko, IPAC10 ~2 MV at ~1.5 GHz ~4 MV at ~0.8 GHz? ~20 MV at ~0.4 GHz ~200 MV at ~0.4 GHz??

9. improving IP overlap for High-Energy LHC?

10. crab cavities for High-Energy LHC

11. formulae for geometric overlap geometric overlap loss factor for equal beams including hourglass & crossing angle ep collision with sze<<szp formula simplifies for round beams: and with

12. boosting beam-beam tune shift additional benefit for HL-LHC • primary motivation for KEKB crab cavities • actual beam-beam tune shift increased by ~20% • SPS collider experience • weak dependence on crossing angle, but • f range of interest was not explored, and • SPS experience not fully relevant for LHC • HL-LHC: INFN-BINP simulations (Lifetrac code) • resonance suppression by LHC crab cavities • HL-LHC: KEK simulations (BBWS code) • beam-beam lifetime boosted 10 times!

13. SPS collider experience historical experiments at SPS collider K. Cornelis, W. Herr, M. Meddahi, “Proton Antiproton Collisions at a Finite Crossing Angle in the SPS”, PAC91 San Francisco f~0.45 qc=500 mrad f≥0.7 tests up to f>0.7 showed (almost) no additional beam-beam effect present nominal LHC: f~0.64, upgrade: f≥1.0-4.0 !?? qc=600 mrad small emittance

14. HL-LHC: INFN-BINP simulation M. Zobov, D. Shatilov collisions with crossing angle frequency map analysis of Lifetrac simulation resonances parameters: ex,y =0.5 nm E= 7 TeV bx= 30 cm, by= 7.5 cm, sz= 11.8 cm, qc= 315 mrad (f=1.5), Nb= 4.0x1011, Qs=0.002, DQx,y~ -0.0065, single IP crab crossing resonance free!

15. (HL-)LHC: KEK simulation collisions with 280 mrad crossing angle crab crossing K. Ohmi 2 IPs 2 IPs simulated luminosity lifetime with crab crossing is 10 times better than without crab crossing

16. luminosity leveling second motivation for HL-LHC • changing b*, Dx*, or qc during the store • → to reduce event pile up & IR peak power deposition • → to maximize integrated luminosity • leveling with crossing angle has advantages • increased average luminosity, operational simplicity • (J.-P. Koutchouk) • natural option for crab cavities • leveling with Dx* already used for ALICE in 2010 • two leveling strategies for HL-LHC: • (1) constant luminosity • (2) constant beam-beam tune shift

17. optimum run time & av. luminosity F. Zimmermann leveling 2 → exponential L decay, w decay time teff (not teff/2)

18. leveling – example evolution b*=14 cm, Nb=2.3x1011, Tta=5 h luminosity [1034 cm-2s-1] |DQ| F. Zimmermann, Chamonix 2010 time [h] time [h] no leveling DQ=const L=const no leveling DQ=const L=const

19. leveling – example numbers F. Zimmermann, Chamonix 2010

20. leveling – other example numbers F. Zimmermann, Chamonix 2010

21. avoiding off-center collisions second motivation for LHeC • RF beam loading in LHC will shift longitudinal bunch position across each bunch train and around the ring (abort gap) • offset is almost ±1 cm at ultimate intensity • LHeC e- beam will not experience the same beam loading • with crossing angle longitudinal p offset translates into transverse offset of e-p collision point by ±5 mm/ mrad • p crab cavities keep the collision centered for all bunches despite beam loading

22. LHC longitudinal bunch position due to beam loading (1 cm = 33 ps) ultimate bunch intensity +/- 0.8 cm maximum offset for example: 8 mrad x 0.8 cm / 2 = 64 mm offset collision Joachim Tuckmantel, 2ndEuCARDAccNetRFTech workshop, 2 Dec. 2010

23. applications of crab cavities • crabbing of colliding beams at the IP - improving geometric overlap - boosting beam-beam tune shift - luminosity leveling • - avoiding off-center collisions from beam loading • off-momentum cleaning • bunch compression

24. off-momentum cleaning • at top energy use LHC crab cavity as “AC dipole” for off-momentum particles (Stephane Fartoukh, 2009) • collimate only in IR7, and use IR3 phase to push b* • energy loss per turn ~10-9 ; with resonance width of • Dd~10-6-10-5 one has 1000-10,000 turns for excitation (Yi-Peng Sun) • effective AC dipole frequency Qacc=fCC/f0h d ; • with fCC=800 MHz, d=10-3: Qacc≈0.025 ; • 8 GHz crab cavity excites around Q≈0.03 • (Stephane Fartoukh , Yi-Peng Sun) • must exploit higher-order resonance to use 800 MHz • collimation efficiency to be verified

25. off-momentum cleaning - principle Yi-Peng Sun

26. off-momentum cleaning - principle Yi-Peng Sun excitation must be fast compared with energy loss from synchrotron radiation

27. off-momentum cleaning - simulation Yi-Peng Sun

28. applications of crab cavities • crabbing of colliding beams at the IP - improving geometric overlap - boosting beam-beam tune shift - luminosity leveling • - avoiding off-center collisions from beam loading • off-momentum cleaning • bunch compression

29. crab cavities for bunch compression conventional bunch compression [e.g. SLC, CTF-2/3] chicane/arc with momentum dependent path length conventional RF cavity x-zemittance exchange with crab cavity [P. Emma et al, for LCLS, 2002] deflecting RF cavity chicane with dispersion & momentum dependent path length SPS: ez~4 mm ex,y~8 nm

30. perspectives • numerous intriguing applications of crab cavities enable various future colliders or can push their performance to new limits: • LHC, HL-LHC, LHeC, HE-LHC, eRHIC, EIC,... • crab cavities improve geometric overlap, boost the beam-beam limit (with negligible effect of parasitic collisions), level the luminosity, mitigate beam loading, assist in beam cleaning and help to shorten bunches for even more advanced colliders (PD-PWA)

31. conclusion: many crabs in our future thank you for your attention