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SPS Experiments on Long-Range Beam-Beam Compensation

SPS Experiments on Long-Range Beam-Beam Compensation. G. Burtin, J. Camas, G. de Rijk, G. Ferioli, J.-J. Gras, S. Jackson, J.-P. Koutchouk, J. Wenninger, F. Zimmermann, … with help from lots of groups!. Summary Motivation LHC & SPS Simulations Scaling. MDs in 2002&2003 BCT, PMT

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SPS Experiments on Long-Range Beam-Beam Compensation

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  1. SPS Experiments on Long-Range Beam-Beam Compensation G. Burtin, J. Camas, G. de Rijk, G. Ferioli, J.-J. Gras, S. Jackson, J.-P. Koutchouk, J. Wenninger, F. Zimmermann, … with help from lots of groups! • Summary • Motivation • LHC & SPS Simulations • Scaling • MDs in 2002&2003 • BCT, PMT • Future Devices • Summary again J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  2. Summary • SPS BBLR Set Up models Long-Range Beam-Beam Collisions • in the LHC; so far 3+3 MDs performed in 2002 & 2003 • Tune shift & orbit distortions well understood; they allow precise • determination of beam-wire distance • Beam lifetime and loss measurements indicate LHC parameters • at the edge (10% less crossing angle -> beam lifetime of 4 h) • Clear shrinkage of emittance due to BBLR & its dependence on • current and distance; using calibration by scraper, this was • converted into diffusive aperture (d.a.); Irwin’s scaling law • confirmed (d.a.~Sqrt(I)); d.a. might be only 2s in LHC?! • Direct diffusion measurements started (limited by PMT • signals, & by scraper speed & software), so far difficult • Further MDs (upgraded scraper) & analysis (e.g., 1000 turns) • foreseen • Two more devices in 2004 will demonstrate correction efficiency & • also allow comparison of various crossing schemes J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  3. Long-Range Beam-Beam Collisions • perturb motion at large betatron amplitudes, where particles come close to opposing beam • cause ‘diffusive aperture’ (Irwin), high background, poor beam lifetime • increasing problem for SPS, Tevatron, LHC,... that is for operation with larger # of bunches J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  4. and LHC: 4 primary IPs 30 long-range collisions per IP 120 in total partial mitigation by alternating planes of crossing at IP1 & 5 etc. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  5. result of weak-strong simulations for LHC center of other beam Y. Papaphilippou & F.Z., LHC 99 ‘diffusive aperture’ J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  6. 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.

  7. 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! J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  8. Experimental Set-Up 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) J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  9. nominal distance 19 mm (in the shadow of the arc aperture) water cooling J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  10. LHC long-range collisions & SPS wire cause similar fast losses at large amplitudes in simulations SPS wire ‘diffusive aperture’ LHC beam 1 mm/s 1 mm/s ‘diffusive aperture’ effect of the 1-m long wire at 9.5s from the beam center, carrying 267 A current, resembles the total number of long-range collisions in the LHC J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  11. MDs in 2002 and 2003 20/08/2002, 26 GeV/c: IC and PMT reading vs. position (threshold!), tune shift @120 A DQx,y=-/+0.0060 10/09/2002, 26 GeV/c: commissioned new inductive coil, DT >18o at 275 A,blew up ey bydamper chirps (WH), DQ & Dy vs. bump @120 A & 267 A 23/09/2002, 55 GeV/c:blew up ey by damper,vertical aperture problememittance shrinks for beam-wire distances <12 mm, beam losses & lifetime vs. separation 27/06/2003, 26 GeV/c: new dipole corrector,emittance shrinkage if BBLR is excited 04/07/2003, 26 GeV/c: blew up emittance by mismatch, emittance shrinkage vs. wire excitation 21/08/2003, 26 GeV/c: kick pencil beam, emittance shrinkage vs. separation, calibration by scraping, diffusion measurement J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  12. linear optics perturbations: orbit change Dd and tune shift DQ due to wire (or due to other beam) precise control of beam-wire separation! J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  13. MD-2002-3 comparison with MAD prediction (J. Wenninger) orbit kick Qy Qx J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  14. MD-2002-2+3: beam-wire distance derived from tune shift and from orbit change versus prediction prediction J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  15. evidence for diffusion vs. beam-wire distance in SPS MD-2002-3 9 s 9 s background up lifetime drops below 9s! logarithmic scales! LHC at the edge of lifetime drop! compare with LHC simulation: 8 s 9.5 s J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  16. MD-2003-1 final emittance reduced, if wire is excited for large initial emittances it may approach a ~constant value dependence on initial emittance J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  17. dependence on wire current experiment of July 4, 2003, confirms Irwin’s scaling law; beam shrinks since particles at large amplitude are lost J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  18. Final emittance vs bump for 3 different BBLR excitations Reduction in emittance of the left outermost point without excitation is consistent with scraping at an amplitude of (19-13.4)mm = 5.6 mm, corresponding to 2.4 times the rms beam size of 2.3 mm. This is also the dynamic aperture for 267 A w/o bump. dependence on beam-wire separation J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  19. Scraper at +3.05(+ 0.88)mm gives eOUT=1.7 mm, no BBLR IN Scan at 100 ms OUT Scan at 3200 ms Note: orbit bump and LRBB excitation from 1500 ms Bump –11.6 mm for BBLR @67 A gives eOUT=2.2 mm Bump –9.4 mm for BBLR @267 A gives eOUT=1.15 mm J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  20. Abel transformation of wire-scan data gives change in (norm.) amplitude distribution: (Krempl, Chanel, Carli) BBLR 267 A, bump –4.5 mm eout=2.06 mm scraping at 3.06 mm, eout=1.71 mm scraping at 2.06 mm, eout=1.31 mm BBLR 267A Bump –9.4 mm, eout=1.15 mm J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  21. Calibration curve of measured final emittance vs scraper position allows us to estimate effective aperture due to BBLR excitation Calibration: measured final emittance vs. scraper position J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  22. scaling to the LHC – d.a. only 2-3 s? J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  23. Example of BCT & PMT data 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 J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  24. Extension 1: Compensation Goal: demonstrate the correctability of the LR-BB effect for LHC conditions: • Betatron phase shift (~2 degrees) • Wire out of beam aperture (12  instead of 9.5 ) • Excitation error: say 10% Set-up: a second identical device in LLS5 about 2 m away + vertical motion: same quality (vacuum compatibility) + larger safety vs SPS aperture. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  25. Extension 2: Long-Distance Compensation & Crossing Schemes • compensation over long distance with variable phase advance and independent x&y orbit bumps at two wires [y wire]; this will confirm the practicability of the compensation scheme for the LHC with reduced systematic cancellations & explore tolerances • compareeffects of alternating x-y crossings at two locations (LHC baseline) with 2 times stronger collision at 45 degrees - “inclined hybrid crossing” - and with pure vertical or pure horizontal crossing [other 2 wires]; this will probe the sensitivity to the LHC crossing scheme and assess present choice J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  26. schematic of 2nd and 3rd device clearance required to stay in the arc shadow: 19 mm (y), 51.5 mm (x), 26.5 mm (45 deg) J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  27. 2nd & 3rd devices will be mobile with wires in different planes (G. Burtin) J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

  28. Summary • SPS BBLR Set Up models Long-Range Beam-Beam Collisions • in the LHC; so far 3+3 MDs performed in 2002 & 2003 • Tune shift & orbit distortions well understood; they allow precise • determination of beam-wire distance • Beam lifetime and loss measurements indicate LHC parameters • at the edge (10% less crossing angle -> beam lifetime of 4 h) • Clear shrinkage of emittance due to BBLR & its dependence on • current and distance; using calibration by scraper, this was • converted into diffusive aperture (d.a.); Irwin’s scaling law • confirmed (d.a.~Sqrt(I)); d.a. might be only 2s in LHC?! • Direct diffusion measurements started (limited by PMT • signals, & by scraper speed & software), so far difficult • Further MDs (upgraded scraper) & analysis (e.g., 1000 turns) • foreseen • Two more devices in 2004 will demonstrate correction efficiency & • also allow comparison of various crossing schemes J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

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