Panel Discussion

1
Panel Discussion

• future machines higher intensity
• shorter bunch spacings and/or higher
• charge per bunch electron
  cloud!
• CERN activities focus on LHC CLIC
• simulation need proposed experiments
• international collaborations

2
Observed Electron Cloud Threshold vs. Bunch
Spacing Future Proposed Machines
SPS, PS, Tevatron, APS thresholds are all
similar DAFNE and KEKB look better, RHIC
worse extrapolation to shorter spacings?
3

• Hot topics for LHC (and others)
• long-time survival of electrons
• elastic reflection at low energy,
• trapping in magnetic fields,
• electron cloud in cold environment
• efficiency of scrubbing
• minimum secondary emission yield that
• can be reached sustained, scrubbing
• time required, effect of temperature
• and magnetic field, vacuum pressure
• beam stability long-term emittance growth
  
• could set gt10 times tighter limit on
• acceptable e-cloud than heat load
• stabilizing measures, optimized beam parameters

planned activities
benchmarking simulations with experiments in the
SPS (RHIC? B factories?)
SPS experiments
SPS experiments and simulations
improved simulations, SPS experiments
4

• Hot topics for CLIC (and others)
• electron cloud for short spacing
• with significant synchrotron radiation
• impact on equilibrium emittance
• trapping in wiggler field
• efficiency side-effects of countermeasures
• e.g., coating, clearing electrodes or clearing
• fields, antechambers, octupoles, chromaticity,
  
• feedback, operation below threshold or in
• Sam Heifets high current regime
• simulation discrepancies for B factories
• halo generation
• effect on IP spot size

5

• one important simulation need
• reliable prediction of long-term emittance growth
• for the LHC
• include lattice variation around the ring
• consider discontinuous e-cloud regions
• better interface or combination of build-up
• and instability simulations (realistic
• electron distribution, response of
• electron cloud to instability, etc.)
• adequate correct boundary conditions
• (magnetic boundaries? actual apertures)
• inclusion of space charge, impedances,
• beam-beam, feedback, chromaticity, etc.
• benchmarking in experiments

6

• proposed experiments at other labs
• explore electron cloud occurrence in the cold
• sections of RHIC and/or the Tevatron in
• view of LHC commissioning
• study the dependence of e- density
• emittance blow up on (shorter) bunch
• spacing at KEKB and PEP-II LER in view of
• demonstrating LC feasibility
• investigate the effect of wiggler on e- build up
• in PEP-II (KEKB study already done)
• study predicted solenoid resonance at PEP-II
• analyze pieces of PEP-II/KEKB chamber to
• understand (in)efficiency of coating or
  scrubbing
• apply coating test clearing electrodes at the
  ATF

7
strong multipacting in a clean TiN coated Al
chamber, without solenoid, after 7 years of
PEP-II operation!?
e- signal
w/o solenoid
with solenoid
2 A
beam current
(A. Kulikov)
8
European Steering Group on Accelerator RD
(ESGARD) CEA, CERN, CNRS-Orsay, DESY, INFN-LNF,
etc. http//esgard.lal.in2p3.fr/ Within the
SIXTH FRAMEWORK PROGRAMME of the EUROPEAN
UNION Coordinated Accelerator Research in Europe
(CARE) 3 Networking 4 Joint Research Activities
Addressing Electron Cloud N2 Electron Linear
Accelerator Network (ELAN) TESLA and CLIC
(Deputy Coordinator D. Schulte) N4 High Energy
High Intensity Hadron Beams (HEHIHB)
SuperLHC, VLHC (Coordinator F. Ruggiero
Deputy Coordinator for HEHIHB WP3 F.
Zimmermann)
...electron cloud codes need comparisons and
benchmarking by beam measurements and are of
common interest for high-luminosity hadron
colliders and high-intensity synchrotrons
establish a working infrastructure in Europe
parallel to the proposed US-LARP programme,
which has as objective to streamline RD work in
the 3 big national labs in the US with the
additional benefit of contributing to LHC
upgrade studies. A parallel US-LARP and CARE
approach would facilitate further the important
information flow and worldwide collaboration
efforts. excerpt from N4 WP3 proposal
9
Country Number of institutes Number of persons
France 2 9
Germany 5 26
Italy 7 20
Japan 1 6
Netherlands 1 5
Poland 1 2
Spain 1 3
Sweden 1 3
Switzerland 2 4
United Kingdom 1 3
U.S.A. 3 25
Russia 2 4
CERN 1 33
Participants to the CARE N4 Activities
(other collaborations that could address e-cloud
exist, e.g.,Intl ATF Collaboration)
10
Joint abstract on code comparisons submitted to
EPAC2004
Review and Comparison of Simulation Codes
Modeling Electron-Cloud Build Up and
Instabilities E. Benedetto, F. Ruggiero, D.
Schulte, F. Zimmermann, CERN G. Rumolo, GSI, J.
Bellodi, RAL K. Ohmi, S.S. Win, KEK A. Ghalam,
T. Katsouleas, USC V. Decyk, W. Mori, UCLA M.
Furman, LBNL Y. Cai, M. Pivi, SLAC M.
Blaskiewicz, L. Wang, BNL Several computer
codes written at various laboratories are
employed for modeling the generation and the
consequences of an electron cloud. We review
the most popular of these programs, which
simulate either the build of an electron
cloud or the instabilities it produces, and
we compare simulation results for identical, or
similar, input parameters obtained from the
various codes.
other contributors welcome!!