Open Issues from the SPS Long-Range Experiments

1. Open Issues from theSPS Long-Range Experiments Frank Zimmermann US-LARP Beam-Beam Workshop SLAC, 2007 Gerard Burtin, Ulrich Dorda, Gijs de Rijk, Jean-Pierre Koutchouk, Yannis Papaphilippou, Tannaji Sen, Vladimir Shiltsev, Jorg Wenninger, + many others

2. outline • motivation & scaling • single wire as LHC LR simulator (2002-2004) • two wire compensation (2004) • test of crossing schemes (2004) • open questions and 2007 plan

3. Motivation: Long-Range Beam-Beam Compensation for the LHC • To correct all non-linear effects correction must be local. • Layout: 41 m upstream of D2, both sides of IP1/IP5 Phase difference between BBLRC & average LR collision is 2.6o (Jean-Pierre Koutchouk) J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

4. 1st Wire “BBLR” in the SPS Iwire=Nb e c #LR/lwire Tech. Coord. J. Camas & G. Burtin/BDI Help from many groups wire current wire length two 60-cm long wires with 267 A current equivalent to 60 LHC LR collisions (e.g., IP1 & 5)

5. each BBLR consists of 2 units, total length: 2x0.8+0.25=1.85 m nominal distance 19 mm (in the shadow of the arc aperture) water cooling

6. Scaling from LHC to SPS perturbation by wire: relative perturbation: for constant normalized emittance the effect in units of sigma is independent of energy and beta function!

7. in simulations LHC long-range collisions & SPS wire cause similar fast losses at large amplitudes simulation with WSDIFF simulation with WSDIFF SPS wire LHC beam 1 mm/s 1 mm/s diffusive aperture

8. a few technical issues • dedicated ion chambers and PMTs • inductive coil to suppress wire ripple • wire heating computed and verified • emittance blow up by damper or injection mismatch to reproduce LHC or to increase sensitivity • wire scanners, scrapers • dedicated dipole corrector to correct orbit change locally • always correct tune

9. changes in orbit & tunes (2002) → precise measure of beam-wire distance y orbit change J. Wenninger x tune change y tune change

10. non-linear optics • turn-by-turn BPM data after kicks of various amplitude → reduced decoherence time due to wire → tune shift with amplitude, roughly consistent with

11. measuring the “diffusive” or dynamic aperture three types of signals: • lifetime and background • final emittance • scraper-retraction

12. lifetime and background lifetime vs. separation beam loss vs. separation drop in the lifetime and increased losses for separations less than 9s; at 7-8s separation lifetime decreases to 1-5 h

13. initial & final profile wire scans initial/final emittance = 3.40/1.15 mm Abel transformation of wire-scan data gives change in (norm.) amplitude distribution: (Krempl, Chanel, Carli)

14. final emittance mechanical scraping by edge of wire

15. calibration of final emittance by scraper Calibration curve of measured final emittance vs scraper position allows us to estimate effective aperture due to BBLR excitation

16. scaling to LHC – d.a. only 2-3s? larger emittance variation when wire is excited?!

17. effect of wire current on SPS dyn.ap. linear dependence consistent with Irwin scaling law; measured dynamic aperture is smaller than the simulated

18. scraper retraction attempt only BBLR (at 12725 ms), w/o scraping BBLR at 12725 ms, scraping at 13225 ms PMT PMT BCT BCT can we fit a diffusion constant? on the right, scraper position is about 1s; at larger amplitudes the diffusion seems much faster than the speed of the scraper scraper moving to target position already intercepts halo

19. effect of beam-wire distance on lifetime 5th power! extrapolation to LHC beam- beam distance, ~9.5s, would predict 6 minutes lifetime

20. effect at low wire excitation BBLR logbook 4 July 2003 “… We bumped exactly –8.2 mm at the BBLR from cycle# 330616 (this would give 12.1 mm separation between wire center and beam [~5s], corresponding to the latest simulations). The interpolated position with wire off was –8.6 mm. The spread in the BPM readings was about +/-0.2 mm. … The wire current was only -10 A [~2 LR collisions in LHC]. Nevertheless, the losses were high, about 3x106 at the 3rd PMT (last year we had about 106 as the maximum integrated reading). “

21. for 2004 two novel 3-wire BBLRs were built; separated from 1-wire BBLR by about 2.6o(average LR-BBLR phase advance in LHC)

22. G. Burtin remotely movable in Y by 5 mm!

23. two-wire compensation: tune scan Qx=0.31 beam lifetime 3rd no wire 10th 7th 2 wires 4th 1 wire vertical tune nearly perfect compensation what happens here? lifetime is recovered over a large tune range, except for Qy<0.285

24. two-wire compensation: distance scan BBSIM (T. Sen): No compensation beyond ~3mm Measurement: Compensation lost beyond ~2.5mm from optimum

25. “scaled” experiments natural SPS beam lifetime ~30 h at 55 GeV/c ~5-10 min at 26 GeV/c (physical aperture ~4 s) to improve beam lifetime at 26 GeV/c, emittance can be reduced by scraping; lifetime for eN~1.5 mm improves to ~1 h

26. scaled two-wire compensation: lifetime ~69 min. ~36 min. ~61 min. LHC tunes J.-P. Koutchouk

27. crossing schemes

28. crossing schemes – motivation 1 EPAC’04 LHC centre of other beam here tunes w/o beam-beam were held constant diffusive aperture with xx or yy crossing diffusive aperture with alternating crossing simulation comparing xy, xx and yy crossing for two working points

29. xx yy 8s 8.5s simulations for different lattice tunes, located along red line: xy 6.5s crossing schemes – motivation 2

30. model system det(M)>0 det(M)<0 bounded fast escape tune evolution for three trajectories without folding; the motion remains bounded tune evolution for three trajectories with folding; the resonance 1:1 is a direction of fast escape (J. Laskar, PAC2003) schematic of folded frequency map (J. Laskar) EPAC’04 crossing schemes – motivation 3

31. little motion at small amplitudes but particle loss at 6 s nonlinear ‘coupling’ between the planes? but stable sample trajectories projected on amplitude plane tune spread gives incomplete characterization of the dynamics; experimental simulations of the two crossing schemes can be compared at the SPS EPAC’04 crossing schemes – motivation 4

32. xx xy simulations frequency maps for nominal LHC tunes yy thanks to Yannis Papaphilippou for his help in calculating frequency maps! crossing schemes – motivation 5

33. crossing schemes – motivation 6 • in most cases simulated diffusive aperture along diagonal x=y larger for equal-plane crossing than for alternating crossing*, sensitivity to IP-IP phase advance • possible explanations: • different ‘folding’ since xy crossing cancels dodecapole and 20-pole terms in addition to linear tune shift; • (2) twice the number of resonances for xy crossing • *(similar result for y=0 – to be revisited)

34. crossing scheme test – configuration 1 BBLR2x on (strength x2) beam xx BBLR1 off beam BBLR2x on x bump -23 mm BBLR1 on “xy” beam x bump -23 mm BBLR2x off “xy-2” & (strength x2) BBLR1 on (strength x2) “yy” x bump -23 mm

35. xx xy yy xy(x2) simulation simulated diffusive aperture for XX crossing is 10% larger than for ‘quasi-XY’ or ‘quasi-YY’ crossing

36. experiment xx xy yy xy(x2) measured beam lifetime is best for XX crossing, second best for ‘quasi-YY’ crossing, lowest for ‘quasi-XY’ crossing lifetime without wire excitation was comparable to xy case

37. crossing scheme test – configuration 2 BBLR1 (rotated) & BBLR2 (45 degrees) J.-P. Koutchouk BBLR2-45 on BBLR2x-45 off BBLR1 on BBLR1 on (strength x2) “45o45o” beam beam x bump -8.9 mm y bump +11.4 mm “45o135o” BBLR2x-45 off BBLR1 on (strength x2) x bump -8.9 mm y bump +11.4 mm “yy” beam x bump 0 mm y bump +8.5 mm reduced emittance “scaled” experiment

38. yy 45o135o 45o45o simulation simulated diffusive aperture for ‘45o45o’ crossing is worst; at tunes below 0.29 it is best for YY crossing & above 0.30 for ‘45o135o’

39. experiment w/o BBLR yy 45o135o 45o45o measured beam lifetime is worst for ‘45o45o’crossing, and at tunes above 0.3 best for ‘45o135o’crossing relative beam lifetimes consistent with simulations

40. some open questions • scaling from SPS to LHC • strong emittance dependence of lifetime (c.f.Tevatron pbar) • discrepancies between measured & simulated dynamic aperture • breakdown of 2-wire compensation for Qy<0.285 • why 5th power law? (Tevatron: 3rd power, RHIC: 2nd and 4th power); why different & why not higher power?? • some effect observed at very low wire excitation • amplitude-dependent diffusion rate • study sensitivity of final emittance to tune with and without BBLR • discrepancies between simulated and measured lifetime (improved at higher beam energy?) • understand parameters which are out of control or introduce intentional large perturbation (excite sextupoles, octupoles) to reconcile experiments and measurements • wire compensation test with colliding beams (at RHIC) (essential?) • common observable in experiments & simulations? – dynamic aperture! lifetime? • demonstrate that 10-4 stability of pulsed wire can be achieved • crossing scheme conclusions?

41. 2007 SPS MD plan • lifetime/emittance growth vs beam-wire distance at different wire currents • tune scan of wire compensation at higher energy with longer unperturbed lifetimes • study compromise between nominal and PACMAN bunches by partial compensation • use both wires as exciters at different beam-wire separation to mimic LRBB at different beam-beam separation (crucial issue for the early separation upgrade scheme) • beam lifetime vs. beam-wire distance for different tunes to see (understand) whether different power laws found at SPS (^5), Tevatron (^3) and RHIC (^2) and (^4) are tune related • noise studies (if more than 2 MDs) to experimentally verify the simulated precision requirements on a pulsed device • experiments will be performed at two different energies (26 GeV and 55 GeV) to confirm the theoretical scaling law

42. for future wire beam-beam compensators - “BBLRs” -, 3-m long sections have been reserved in LHC at 104.93 m (center position) on either side of IP1 & IP5

43. references • J.-P. Koutchouk, Principle of a Correction of the Long-Range Beam-Beam Effect in LHC using Electromagnetic Lenses, LHC Project Note 223, 2000 • J.-P. Koutchouk, Correction of the Long-Range Beam-Beam Effect in LHC using Electromagnetic Lenses, SL Report 2001-048,  2001 • F. Zimmermann, Weak-Strong Simulation Studies for the LHC Long-Range Beam-Beam Compensation, presented at Beam-Beam Workshop 2001 FNAL; LHC Project Report 502 (2001) • J. Lin, J. Shi, W. Herr, Study of the Wire Compensation of Long-Range Beam-Beam Interactions in LHC with a Strong-Strong Beam-Beam Simulation, EPAC 2002, Paris (2002) • J.-P. Koutchouk, J. Wenninger, F. Zimmermann, Compensating Parasitic Collisions using Electromagnetic Lenses, presented at ICFA Beam Dynamics Workshop on High-Luminosity e+e- Factories ("Factories'03") SLAC; in CERN-AB-2004-011-ABP (2004) • J.-P. Koutchouk, J. Wenninger, F. Zimmermann, Experiments on LHC Long-Range Beam-Beam Compensation in the SPS, EPAC'04 Lucerne (2004) • F. Zimmermann, Beam-Beam Compensation Schemes, Proc. First CARE-HHH-APD Workshop on Beam Dynamics in Future Hadron Colliders and Rapidly Cycling High-Intensity Synchrotrons (HHH-2004), CERN, Geneva, Switzerland, CERN-2005-006, p. 101 (2005) • F. Zimmermann, J.-P. Koutchouk, F. Roncarolo, J. Wenninger, T. Sen, V. Shiltsev, Y. Papaphilippou, Experiments on LHC Long-Range Beam-Beam Compensation and Crossing Schemes at the CERN SPS in 2004, PAC'05 Knoxville (2005) • F. Zimmermann and U. Dorda, Progress of Beam-Beam Compensation Schemes, Proc. CARE-HHH-APD Workshop on Scenarios for the LHC Luminosity Upgrade (LHC-LUMI-05), Arcidosso, Italy (2005) • U. Dorda and F. Zimmermann, Simulation of LHC Long-Range Beam-Beam Compensation with DC and Pulsed Wires  (Talk), RPIA2006 workshop, KEK, Tsukuba, 07-10.03.2006 (2006)  • F. Zimmermann, Possible Uses of Rapid Switching Devices and Induction RF for an LHC Upgrade(Talk),RPIA2006 workshop, KEK, Tsukuba, 07-10.03.2006 (2006) • U. Dorda, F. Zimmermann et al, Assessment of the Wire Lens at LHC from the current Pulse Power Technology Point of View(Talk), RPIA2006 workshop, KEK, Tsukuba, 07-10.03.2006 (2006)