Status of Beam-Beam Task

1
Status of Beam-Beam Task
US LHC Accelerator Research Program
BNL - FNAL- LBNL - SLAC

• Valishev, FNAL
• W. Fischer, Y. Luo BNL
• H.-J. Kim, A. Makarevich, V. Shiltsev, G.
  Stancari, X.Zhang FNAL
• A. Kabel SLAC, A. Romanov BINP
• 04 November 2009
• LARP CM13, Port Jefferson, NY

2
FY09 LARP Beam-Beam Task
The Goal Evaluate the possible benefit to LHC
(RHIC) luminosity from HO beam-beam compensation.

• Experimental studies at the Tevatron
• Installation of the Gaussian profile gun was
  planned
• To experiment with beam to beam alignment
  tolerances
• Attempt tune footprint suppression
• Identify operational problems
• Provide data for comparison with simulations
• Numerical simulations
• Develop and validate codes/machine models using
  existing experimental data
• Provide predictions for RHIC and LHC to support
  E-Lens installation
• Theoretical analysis
• Effect of dispersion and chromaticity on RDTs,
  finite e-beam rigidity

3
Outline of the Talk

• Status of Gaussian Tevatron electron lens
• Beam-beam codes development, validation
• Simulations of head-on compensation at RHIC
• Effect of imperfections
• Simulations of head-on compensation at LHC
• Summary

4
Beam-Beam Effects and BBC at the Tevatron

• Head-on tune spread in proton bunches is larger
  due to 3/1 p/a emittance ratio
• Bunches have different working points due to
  Long-Range BBI

Gaussian TEL can generate dQ0.01
xa0.019
xp0.018
Na
Np
5
Gaussian TEL Progress(A. Romanov, V. Shiltsev,
G. Stancari, A. Valishev, X. Zhang)

• Gaussian gun was installed in TEL-2 on June 20
  (Tevatron shutdown 6/15 9/11). Peak current up
  to 1A (Ne2x1011)
• New TEL-2 BPM software
• Java, faster than old LabView
• Measures positions of individual proton,
  antiproton, e- bunches
• New software for high resolution Tev BPM
• Established electron beam timing, started
  alignment with proton bunches

6
TEL-2 BPMs

• One channel with strong reflections
• Frequency dependence
• Different calibrations and different offsets for
  (anti)protons and electrons

7
Next Steps and Tevatron Beam Time Requirements

• Calibrate BPMs with electrons and protons
• 1 hour end-of-store
• Align electron beam with protons
• 4-6 hours proton-only
• Measure tune-spread changes, effect on beam life
  time
• 2 hours end-of-store, 4-6 parasitic in-store
  studies
• Awaiting Run Coordinators approval for beam time

8
Simulation Tools

• Weak-strong (some codes have strong-strong
  capabilities)
• Essential features
• Linear machine lattice with all IPs and
  separations
• Chromaticity
• Nonlinear elements

• Short-term measures
• tune footprint
• diffusion coefficients, tune diffusion
• resonance driving terms
• short-term dynamic aperture
• 103 turns - fast
• Interpretation of results is not
  straightforward.

• Long-term tracking
• intensity life time
• emittance growth
• 106 107 turns - slow
• The main parameters for evaluation are
  measurable quantities

9
Simulation Tools Continued

• BBSIM (T. Sen, H.-J. Kim FNAL)
• RHIC head-on compensation
• LIFETRAC (D.Shatilov BINP, A. Valishev FNAL)
• RHIC head-on compensation
• LHC head-on compensation (LR collisions also
  included)
• PLIBB (A. Kabel SLAC)
• Configured to run LHC head-on compensation. No
  new results in FY09
• SIXTRACK (F. Schmidt CERN, G. Robert-Demolaize,
  Y. Luo BNL)
• RHIC head-on compensation

10
Benchmarking BBSIM vs. LIFETRAC, RHIC BBC (H.-J.
Kim, A. Valishev FNAL)

• Model differences
• Initial distribution
• BBSIM hollow Gaussian
• Lifetrac weighted Gaussian
• Aperture
• Lattice chromaticity (sextupoles)

• Model similarities
• Machine optics
• Includes multipoles
• Beam parameters
• 3D beam-beam

NO BBC
1/2 BBC
11
Benchmarking BBSIM vs. SimTrack, RHIC BBC (H.-J.
Kim FNAL, Y. Luo BNL)
Also compared Lifetrac and SixTrack in 2D good
agreement
12
RHIC BBC Simulations with SixTrack(Y. Luo, W.
Fischer, G. Robert-Demolaize, R. De Maria BNL)
t5 h
t20 min
Also did phase and Beam mismatch scans (see Yuns
talk)
nonlinear IR errors and arc sextupoles included,
4D BB at IP6 and IP8, zero length elens at IP10,
core tunes at (0.67,0.68) and chromaticities of
1 for all cases, 250 GeV, 6400 macroparticles in
Gaussian distribution
With Nb2e11 losses are less than 3/hour
13
RHIC BBC Simulations with BBSIM(H.-J. Kim, T.
Sen FNAL)

• SEFT Electron Lens
• Flat top edge is 4sigma
• Small Ne reduces beam loss much

• Gaussian Electron Lens
• Same beam size as IP10's
• Small Ne reduces beam loss
• Ne lt 0.5 Nip Np

NO BBC

• 1x bbc beam-beam compensation with Ne Nip
  Np 22E11

Is this a tune effect?
14
RHIC BBC Simulations with BBSIM Continued
Np3e11 Np2e11
BBCon BBCoff
BBC off Intensity loss in /hour vs. lattice
tunes
Np2e11, se2sp, full compensation Intensity loss
in /hour vs. lattice tunes
15
RHIC BBC Simulations with BBSIM Continued
BBCon BBCoff
Np2e11, se1sp, half compensation Intensity loss
in /hour
Np2e11, se1sp Relative intensity loss over 106
turns
16
RHIC BBC Simulations with BBSIM Continued
BBCon BBCoff
BBCon BBCoff
Np2e11, SEFT, full compensation Intensity loss
in /hour vs. lattice tunes
Np2e11, SEFT, half compensation Intensity loss
in /hour vs. lattice tunes
17
Effect of Imperfections - Misalignment

• Length of interaction region in the EL is much
  smaller than beta-function - consider ELs as
  short kick element.
• Model of imperfect alignment - split the EL beam
  into several slices and sum the kicks.

Proton orbit
Electron beam
Slices
Nslice 1 2 3 4 5
Difference between exact numerical integral and
slice kicks for -1s pitch
18
Tune Spread Compensation with Misalignment shift
in X-Z plane scan
Gaussian
SEFT

• Full compensation.
• xi, xf varied from 0 to 2s
• yi 0, yf 0

19
RHIC BBC Simulations with Misalignment(A.
Valishev FNAL)
Dx/sp
Np2e11, sp0.3mm, se0.45mm Parallel offset in
horizontal plane, 3 slices
20
LHC BBC Simulations with Lifetrac(A. Valishev
FNAL)
t200 h
t130 h

• Np2.3x1011
• 4 IPs
• No FF nonlinearities

t80 h
Shiltsev
20
LHC Electron Lenses FNAL 06/04/08
21
LHC BBC Simulations with Lifetrac Continued
BBCon BBCoff
BBCon BBCoff
Np2.3e11, sesp half compensation Intensity loss
in /hour vs. lattice tunes
Np2.3e11, se1.5x sp half compensation Intensity
loss in /hour vs. lattice tunes
Shiltsev
21
LHC Electron Lenses FNAL 06/04/08
22
LHC BBC Simulations with Lifetrac Continued
BBCon BBCoff
Min. loss (/hour) EL off 27 EL on 8
Np3.45e11, se sp half compensation Intensity
loss in /hour vs. lattice tunes
From Tevatron experience losses lt 10/hour are
tolerable
Shiltsev
22
LHC Electron Lenses FNAL 06/04/08
23
Summary

• Gaussian gun in TEL-2 (finally!), beam studies
  started. First results may become available in
  2009
• 3 simulation codes (BBSIM, Lifetrac, SixTrack)
  well developed and demonstrated good agreement in
  test cases. Expecting some results from PlibB
  shortly.
• Simulations of head-on BBC at RHIC predict
  significant beam life time improvement at
  Npgt2.5e11. Very little beam-beam effect at
  Nplt2e11.
• Simulations of beam-beam effects at the LHC show
  that
• At Np2.3e11 (2x nominal) losses do not exceed
  1/hour upgrade path?
• At Np3.45e11 (3x nominal) head-on BBC with a
  single EL placed at bbc (wire) location is
  efficient and losses can be kept under 10/hour
• Need to ramp up collaboration with CERN