Vladimir Shiltsev

Vladimir ShiltsevVladimir Shiltsev

Considerations on Considerations on Beam-Beam Compensation Beam-Beam Compensation with Electron Lenses in LHCwith Electron Lenses in LHC

April 27, 2006April 27, 2006

4/27/06, eBBC in LHC - Shiltsev 2

Content:Content:

The idea, how it works, Tev experience

eBBC in LHC and RHIC

Possible plan to proceed


Original Idea Was (1997)…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 “


Head-on and Long-Range Head-on and Long-Range BBCompensationBBCompensation

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

dc

a

Yu.Alexahin


E-lenses in RHIC and LHCE-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


basics of head-on beam-beam basics of head-on beam-beam compensationcompensation

• 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?


e-Shape controle-Shape control

Gaussian

Optimized

(6-Gauss)

Just an example

(see footprint on previous slide)


Challenges of Head-On Challenges of Head-On CompensationCompensation

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?


eLens configurationseLens configurations


TEL-2 B-field line straightnessTEL-2 B-field line straightnessS.KamerdzhievX.L.ZhangV.Shiltsev


Proposed Action PathProposed 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$


Step 1: Theory and Simulations: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


slidesslidesbackup


Proposed Action PlanProposed 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)


E-lenses in RHIC and LHC: General E-lenses in RHIC and LHC: General Considerations Considerations

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a=1.7mmL=2mE=980GeVbeta_e=0.2

Scaling: need a_e = a_p and about same dQ~0.01 Two factors:

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yxnea

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For RHIC: beta_x = 20 m for Tev: beta_x=100 gamma=250 gamma=1000Thus (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=1000Thus (B_c/B_main)=1/3.5 x (B/B)_Tevatron not easy,

but doable


Tevatron Electron Lens #1 (TEL-1) Tevatron Electron Lens #1 (TEL-1)

+ HV Modulator, HV+HC PSs, Cryo, QPs, Vacuum, Controls, Diagnostics, Cables

90 deg bend


Tevatron Electron Lens #1 in the Tevatron Tunnel, sector F48Tevatron Electron Lens #1 in the Tevatron Tunnel, sector F48


Tuneshift dQTuneshift dQhorhor=+0.009 by TEL=+0.009 by TEL

Three p-bunches in the Tevatron, the TEL acts on one of them


Beam-Beam at Low-beta Now: ConfinedBeam-Beam at Low-beta Now: Confined

7th order resonances:

Q=4/7=0.571 -

HIGH LOSSES


Q=7/12=0.583 -

Bad lifetime


Q=3/5=0.600 –

EMITTANCE BLOWUP

p

pbar

025.04

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pprN

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Vladimir Shiltsev