Vladimir Shiltsev Considerations on Beam-Beam Compensation with Electron Lenses in LHC April 27, 2006
4/27/06, eBBC in LHC - Shiltsev 2Content: 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 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
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 (~ ns)=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 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 = mm … or donut shape?
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)
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 mm is doable, though not easy Keeping beam straight within mm Beam-beam centering within mm Will bending sections do harm?
4/27/06, eBBC in LHC - Shiltsev 9 eLens configurations 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 ~1300k$ M&S Demonstrate head-on compensation ~200k$ SWF Build TELs for LHC ~1100k$ M&S Install TELs in LHC and commission ~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 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
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
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 dQ hor = 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 7 th order resonances: Q=4/7= HIGH LOSSES 12 th order resonances: Q=7/12= Bad lifetime 5 th order resonances: Q=3/5=0.600 – EMITTANCE BLOWUP p pbar