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Beam-Beam Compensation Strategies Using Electron Lenses in the LHC

This document discusses the concept and implementation of electron beam-beam compensation (eBBC) in the Large Hadron Collider (LHC) and its applicability based on Tevatron experiences. It covers the need for electron lenses (TELs) to counteract beam-beam tune shifts caused by proton interactions, presenting a feasible plan to explore the effectiveness of this compensation method. The significance of electron beam profile, stability, and operational parameters is emphasized, with proposed action steps for feasibility studies and further developments in the upcoming years.

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Beam-Beam Compensation Strategies Using Electron Lenses in the LHC

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

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

  4. a b d c 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 Yu.Alexahin 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 4/27/06, eBBC in LHC - Shiltsev

  6. 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? 4/27/06, eBBC in LHC - Shiltsev

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

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

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

  13. slides backup 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) 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 m for 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 m for Tev: beta_x=100 gamma=7000 gamma=1000 Thus (B_c/B_main)=1/3.5 x (B/B)_Tevatron  not easy, but doable 4/27/06, eBBC in LHC - Shiltsev

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

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

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

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

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