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
4/27/06, eBBC in LHC - Shiltsev 3
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 “
4/27/06, eBBC in LHC - Shiltsev 4
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
4/27/06, eBBC in LHC - Shiltsev 5
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
4/27/06, eBBC in LHC - Shiltsev 6
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?
4/27/06, eBBC in LHC - Shiltsev 7
e-Shape controle-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 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?
4/27/06, eBBC in LHC - Shiltsev 9
eLens configurationseLens configurations
4/27/06, eBBC in LHC - Shiltsev 10
TEL-2 B-field line straightnessTEL-2 B-field line straightnessS.KamerdzhievX.L.ZhangV.Shiltsev
4/27/06, eBBC in LHC - Shiltsev 11
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$
4/27/06, eBBC in LHC - Shiltsev 12
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
4/27/06, eBBC in LHC - Shiltsev 13
slidesslidesbackup
4/27/06, eBBC in LHC - Shiltsev 14
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)
4/27/06, eBBC in LHC - Shiltsev 15
E-lenses in RHIC and LHC: General E-lenses in RHIC and LHC: General Considerations Considerations
pe
pee
e
eyx
yx ace
rLJdQ
2
,
,
12
main
cathodecathodee B
Baa 22
a=1.7mmL=2mE=980GeVbeta_e=0.2
Scaling: need a_e = a_p and about same dQ~0.01 Two factors:
p
yxnea
,2
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
4/27/06, eBBC in LHC - Shiltsev 16
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
4/27/06, eBBC in LHC - Shiltsev 17
Tevatron Electron Lens #1 in the Tevatron Tunnel, sector F48Tevatron Electron Lens #1 in the Tevatron Tunnel, sector F48
4/27/06, eBBC in LHC - Shiltsev 18
Tuneshift dQTuneshift dQhorhor=+0.009 by TEL=+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: ConfinedBeam-Beam at Low-beta Now: Confined
7th order resonances:
Q=4/7=0.571 -
HIGH LOSSES
12th order resonances:
Q=7/12=0.583 -
Bad lifetime
5th order resonances:
Q=3/5=0.600 –
EMITTANCE BLOWUP
p
pbar
025.04
p
pprN