Open Issues from the SPS Long-Range Experiments

Transcription

1 Open Issues from the SPS 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 ( ) 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 APC meeting, , LRBB Phase difference between BBLRC & average LR collision is 2.6 o (Jean-Pierre Koutchouk) J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

4 1 st Wire BBLR in the SPS Tech. Coord. J. Camas & G. Burtin/BDI I wire =N b e c #LR/l wire wire current wire length Help from many groups 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: 2x =1.85 m nominal distance 19 mm (in the shadow of the arc aperture) water cooling

6 Scaling from LHC to SPS ) ( 2 ' d y ec I l r y w w p = Δ γ = Δ da w w p y n I ec l r y ) ~ ( 2 ' ' γε σ relative perturbation: for constant normalized emittance the effect in units of sigma is independent of energy and beta function! perturbation by wire:

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 y tune change Δd ΔQ = x, y γec = ( d + Δd ) tan( π ( Q + ΔQ ) m r p β y I w l w r β x, yi wlw 1 2πγec d p y y ( d + Δ ) 2 J. Wenninger x 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 ΔQ x 3 4 I w l w r γec p β d x ˆ 2 y 4 ΔQ y 3 8 I w l w r γec p β d x ˆ 2 y 4

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 9σ; at 7-8σ separation lifetime decreases to 1-5 h

13 initial & final profile wire scans initial/final emittance = 3.40/1.15 μm Abel transformation of wire-scan data gives change in (norm.) amplitude distribution: ρ( A) = 2A R A dη g ' 2 η ( η) A 2 (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 2-3σ? 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 ms), w/o scraping BBLR at ms, scraping at ms BCT PMT PMT BCT on the right, scraper position is about 1σ; at larger amplitudes the diffusion seems much faster than the speed of the scraper can we fit a diffusion constant? scraper moving to target position already intercepts halo

19 effect of beam-wire distance on lifetime 5 th power! τ d 5 ms σ 5 extrapolation to LHC beambeam distance, ~9.5σ, 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# (this would give 12.1 mm separation between wire center and beam [~5σ], 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 3x10 6 at the 3rd PMT (last year we had about 10 6 as the maximum integrated reading).

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

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

23 two-wire compensation: tune scan 3rd beam lifetime Q x =0.31 4th 10th 7th no wire 2 wires 1 wire what happens here? nearly perfect compensation vertical tune lifetime is recovered over a large tune range, except for Q y <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 σ) to improve beam lifetime at 26 GeV/c, emittance can be reduced by scraping; I w ~ ε, lifetime for ε N ~1.5 μm improves to ~1 h d ~ ε

26 scaled two-wire compensation: lifetime lifetime in s ~69 min. compensation LHC tunes Lifetime versus cycle number ~36 min. excitation no beam - beam ~61 min cycle number J.-P. Koutchouk

27 crossing schemes

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

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

30 det(m)>0 det(m)<0 model system bounded fast escape M Q = I 2 H = 2 I x, y x, y x, y 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) crossing schemes motivation 3 EPAC 04

31 nonlinear coupling between the planes? but stable little motion at small amplitudes but particle loss at 6 σ 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 crossing schemes motivation 4 EPAC 04

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

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: (1) 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 BBLR2x on beam xx BBLR1 off x bump -23 mm xy BBLR1 on x bump -23 mm BBLR2x off beam & xy-2 (strength x2) yy BBLR1 on (strength x2) x bump -23 mm

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

36 xx experiment yy xy 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) BBLR2-45 on J.-P. Koutchouk BBLR2x-45 off BBLR1 on BBLR1 on (strength x2) beam beam 45 o 135 o x bump -8.9 mm y bump mm 45 o 45 o x bump -8.9 mm y bump mm BBLR2x-45 off BBLR1 on (strength x2) beam yy reduced emittance scaled experiment x bump 0 mm y bump +8.5 mm

38 yy 45 o 135 o 45 o 45 o simulation simulated diffusive aperture for 45 o 45 o crossing is worst; at tunes below 0.29 it is best for YY crossing & above 0.30 for 45 o 135 o

39 w/o BBLR yy experiment 45 o 135 o 45 o 45 o measured beam lifetime is worst for 45 o 45 o crossing, and at tunes above 0.3 best for 45 o 135 o 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 Q y <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 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 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 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 , 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, (2006) F. Zimmermann, Possible Uses of Rapid Switching Devices and Induction RF for an LHC Upgrade (Talk), RPIA2006 workshop, KEK, Tsukuba, (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, (2006)