1. Vladimir Shiltsev Considerations on Beam-Beam Compensation with Electron Lenses in LHC April 27, 2006

2. 4/27/06, eBBC in LHC - Shiltsev 2Content:  The idea, how it works, Tev experience  eBBC in LHC and RHIC  Possible plan to proceed

3. 4/27/06, eBBC in LHC - Shiltsev 3 Original Idea Was (1997)… “…to compensate (in average) space charge forces of positevely charged protons acting on antiprotons in the Tevatron by interaction with a negative charge of a low energy high-current electron beam “

4. 4/27/06, eBBC in LHC - Shiltsev 4 Head-on and Long-Range BBCompensation  Tev Run II: 36x36 bunches in 3 trains  compensate beam-beam tune shifts  a) Run II Goal  b) one TEL  c) two TELs  d) 2 nonlinear TELs  requires  1-3A electron current  stability dJ/J<0.1%  e-pbar centering  e-beam shaping b d c a Yu.Alexahin

5. 4/27/06, eBBC in LHC - Shiltsev 5 E-lenses in RHIC and LHC  In Tevatron TELs to compensate bunch-by-bunch tune shift due to parasitic beam-beam interactions   Requires pulsed e-beam (~400-800ns)=expensive HV modulator  Need 2 lenses – one vert and one horizontal at unequal and large beta’s  Better have much wider e-beam than p-beam + ~uniform j(r)  Needed dQ~0.006 ; max tuneshift dQ~0.009 achieved  LHC (and RHIC) can benefit from head-on beam-beam compensation   Electrons compensate prtons – that’s good!  DC beam = no HV pulsers! (even better)  Need 2 lenses – one per beam; at equal beta’s  Large beta is ~OK (at least better than in Tevatron as sigma_z/beta* is not as big as in Tev where it is ~2)  E-beam j(r) should be Gaussian to match protons at IPs – easy!  Need dQ_max~0.01 which is achievable  see next slide

6. 4/27/06, eBBC in LHC - Shiltsev 6 basics of head-on beam-beam compensation basics of head-on beam-beam compensation If beam sizes and shapes are matched (e=p) for LHC N_p=1.1e11, N_ip=4, for 10kV electrons (beta=0.2) one needs N_e=4.4e11 or J_e=1.2 A in L=3 m long e-beam approx Gaussian e-current distribution with rms = 0.3-0.5 mm … or donut shape?

7. 4/27/06, eBBC in LHC - Shiltsev 7 e-Shape control e-Shape control Gaussian Optimized (6-Gauss) Just an example (see footprint on previous slide)

8. 4/27/06, eBBC in LHC - Shiltsev 8 Challenges of Head-On Compensation  Total current is not a challenge  Optimum beam profile (vs bunchlength/beta*, Qx,y) -?  Compression to 0.3-0.5 mm is doable, though not easy  Keeping beam straight within 0.03-0.05 mm  Beam-beam centering within 0.03-0.05 mm  Will bending sections do harm?

9. 4/27/06, eBBC in LHC - Shiltsev 9 eLens configurations eLens configurations

10. 4/27/06, eBBC in LHC - Shiltsev 10 TEL-2 B-field line straightness S.Kamerdzhiev X.L.Zhang V.Shiltsev

11. 4/27/06, eBBC in LHC - Shiltsev 11 Proposed Action Path  Form an LHC eCompensation Task Force with a charge to perform feasibility study in ~1 year  Goal is to explore parameter space and effectiveness of head-on BBC in LHC and RHIC Cost: ~1.5FTE(~200k$) in SWF; 50% for LARP In case of positive outcome, next steps may include:  Design of the TEL for RHIC 2007 ~200k$ SWF  Construction of TEL for RHIC 2008-2009~1300k$ M&S  Demonstrate head-on compensation 2009-2010~200k$ SWF  Build TELs for LHC 2011-2012~1100k$ M&S  Install TELs in LHC and commission 2012-2014~200k$ SWF Total: 3,000k$

12. 4/27/06, eBBC in LHC - Shiltsev 12 Step 1: Theory and Simulations:  Will Gaussian or truncated Gaussian e-current density distribution work (improve lifetime and reduce diffusion rates)?  Straightforward tracking with a weak-strong code  Is partial distribution helpful?  Is there a better distribution?  from first principles, theory, analytical consideration  Effects are beta_TEL/beta*/sigma_z; or dP/P  check in numerical tracking  Importance of e-pbar(p) interaction in bending sections  Which of three configurations is better?  Is the choice tune dependent?  Lifetime deterioration due to e-p misalignment:  e-beam straightness tolerances  relative e-p displacement, angle  Effect of low-frequency variations dJ, dX on beam lifetime  Ion cleaning efficiency tolerances  Cross-interaction with wires in LHC – if there is any  e-beam effect on coherent stability or strong-strong beam-beam effects

13. 4/27/06, eBBC in LHC - Shiltsev 13 slides backup

14. 4/27/06, eBBC in LHC - Shiltsev 14 Proposed Action Plan  Calibrate TEL-2 BPMs with stretch wire (Vic, Seva, Brian)  Measure SEFT profile (Seva)  Assemble TEL-2 vacuum system and bake (Gennady & John F)  Perform EoS and SoS studies with TEL-1 (ZXL, VS, Seva)  Get the current, study transmission vs B_gun/B_main (Seva, XL)  Study e-beam orbit vs current (same)  Tracking studies with LIFETRAC (Sasha Valishev)  Calibrate TEL-2 BPMs with short e-pulses (Vic and Seva)  Measure TEL-2 e-beam profile (Seva, Vic)  Commission MARX generator pulser (Howie & we)  Move & install TEL-2 FY06 during shtdn (Gennady, MSupp, et al)  Commission TEL-2 with 980 GeV p-beam, studies with 2 TELs (all)  Build parts for TEL-1 modification (Gennady, Seva, VS)  Modify TEL-1 in FY07 shutdown (as in FY06)

15. 4/27/06, eBBC in LHC - Shiltsev 15 E-lenses in RHIC and LHC: General Considerations a=1.7mm L=2m E=980GeV beta_e=0.2 Scaling: need a_e = a_p and about same dQ~0.01 Two factors: For RHIC: beta_x = 20 mfor Tev: beta_x=100 gamma=250 gamma=1000 Thus (B_c/B_main)=4/5 x (B/B)_Tevatron  easy! For LHC: beta_x = 200 mfor Tev: beta_x=100 gamma=7000 gamma=1000 Thus (B_c/B_main)=1/3.5 x (B/B)_Tevatron  not easy, but doable

16. 4/27/06, eBBC in LHC - Shiltsev 16 Tevatron Electron Lens #1 (TEL-1) + HV Modulator, HV+HC PSs, Cryo, QPs, Vacuum, Controls, Diagnostics, Cables 90 deg bend

17. 4/27/06, eBBC in LHC - Shiltsev 17 Tevatron Electron Lens #1 in the Tevatron Tunnel, sector F48

18. 4/27/06, eBBC in LHC - Shiltsev 18 Tuneshift dQ hor =+0.009 by TEL  Three p-bunches in the Tevatron, the TEL acts on one of them

19. 4/27/06, eBBC in LHC - Shiltsev 19 Beam-Beam at Low-beta Now: Confined 7 th order resonances: Q=4/7=0.571 - HIGH LOSSES 12 th order resonances: Q=7/12=0.583 - Bad lifetime 5 th order resonances: Q=3/5=0.600 – EMITTANCE BLOWUP p pbar