How to Use a SAFEM

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Electron Cloud update and Overview of
International Effort Contributions from M. Pivi
(SLAC), M. Palmer (Cornell), C. Celata (LBNL), A.
Markovic (Rostock Univ.) People involved
ILC D. Arnett, G. Collet, R. Kirby, N. Kurita,
B. Mckee, M. Morrison, P. Raimondi, T.
Raubenheimer, J. Seeman, L. Wang (SLAC), D.
Rubin, D. Rice, L. Schachter, J. Codner, E.
Tanke, J. Crittenden (Cornell), U. Van Rienen, G.
Pöplau (Rostock Univ.), J.L. Vay, M. Furman
(LBNL), K. Ohmi, Y. Suetsugu (KEK), R. Wanzenberg
(DESY), F. Zimmermann (CERN), A. Wolski (Cockroft
Uniiv.), B. Macek (LANL), C. Vaccarezza, S.
Guiducci (Frascati)
SLAC, May 9, 2006
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Simulations Wiggler
aperture increase
2 x 6km DR Beneficial effect of increasing the
wiggler chamber aperture.
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Simulations Compare options
Cloud density near (r1mm) beam (m-3) before
bunch passage, values are taken at a cloud
equilibrium density. Solenoids decrease the cloud
density in DRIFT regions, where they are only
effective. Compare options LowQ and LowQtrain
gaps. All cases wiggler aperture 46mm.

• SELF-CONSISTENT SIMULATION CODE IS UNDER
  DEVELOPMENT at SLAC

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RD Projects, SLAC
Ongoing projects at SLAC, chamber installations
FY07 projects
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SEY test chamber
Inner view of chamber and sample locations
Sample exposed to PEP-II Synch. radiation And
electron conditioning
Electron cloud energy spectrum analyzer assembly
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Macro fins chamber

• Status Ongoing extrusion of fin and no-fin
  chambers. 4 chambers will be installed in PEP-II
  LER in 2006.
• Simulations Secondary electron yield 0.8

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SEY tests chamber
ARC STRAIGHT
Fin chambers
e
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RD Projects
Ongoing projects at SLAC, chamber installations
FY07 projects
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Curved clearing electrodes simulations
Simulation unsing POSINST code of electron cloud
build-up and suppression with clearing
electrodes. ILC DR positron assuming one single
6 km ring.
BEND chamber with curved clearing electrodes
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Curved clearing electrodes effect
Electron starts at rest near wall BUNCH WEAK
CLEARING ELECTRODE EFFECT electron is first
accelerated to the center by the beam and then
decelerated by the 10V electrode. It is close to
center when the following bunch pass by. (10V is
similar to 0V) ? Electron cloud build-up.
Clearing electrode
10V
Electron starts at rest near wall BUNCH
STRONG CLEARING ELECTRODE EFFECT electron is
first accelerated to the center by the beam and
then is attracted back to the 100V electrode
after 3 ns, much before the next bunch passage. ?
Electron cloud is strongly suppressed !
100 V
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Clearing electrodes chamber

• Suppress the electron cloud in BEND and WIGGLER
  (QUAD) sections. Perfect !
• TESTS
• DESIGN Optimized, kicker stripe line concept.
• LOCATION PEP-II LER PR12 Straight CELL 8, in a
  DEDICATED 2 or 4 BENDS chicane.
• MATERIAL Chamber with electrodes and diagnostics
  SLC Final Focus correctors at 2 kG.
• Alternative location existing PEP-II PR02 BEND
  BCC4L.
• Advantages extra beam size monitor for PEP-II
  LER (HER) comes at low cost.
• Manufacturing and designing should start as soon
  as possible !
• ILC and PEP-II, collaboration Cornell, KEK (!?)

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Micro-fins photo-etching test samples
50mm and 25mm fins width
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EMEGA
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Electron Cloud Studies at CESR

• Recent Measurements at CESR
• Observed large e emittance among other
  indicators
• Also interesting from ILC DR perspective
• New instrumentation coming on line (CESR-c and
  ILC driven)
• Key CESR Parameters
• Circumference 768.44 m
• Revolution frequency 390.13 kHz
• RF frequency 499.76 MHz
• Harmonic number 1281
• 1281/7 183 bunches
• Spacing between bunches in train 14 ns

• Instrumentation
• Bunch-by-bunch tune monitor
• Capable of sampling up to 366 bunches in parallel
• Used for measurements on the following pages
• Bunch-by-bunch beam size monitor
• New capability just coming on line for
  multi-bunch operation
• First measurements made and being analyzed a
  expect updates soon!

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Positron Measurements

• Positrons _at_ 5.3 GeV
• Single train of 45 bunches with 14 ns spacing
• NOTE at highest bunch currents, filling of
  bunches
• gt 20 no longer uniform
• Plots
• Top Bunch Tune (kHz) vs Bunch
• Bottom BPM ADC level vs Bunch (note missing
  bunches at high bunch currents)

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Electron Measurements

• Electrons _at_ 5.3 GeV
• Single train of 45 bunches with 14 ns spacing
• NOTE Filling generally more uniform than for e
• Also includes reference plot of positrons from
  previous page (0.5 mA/bunch)
• Smaller effect observed than for e
• Opposite sign of tune variation consistent with
  ECE for both species

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LBNL brings a 3-D, Fully Self-Consistent
Code to the ILC Ecloud Effort
WARP (LLNL/LBNL) has been added to POSINST
PIC code - self-consistent (beam electrons),
time-dependent 3D with optional 2D models
(x-y, r-z) Arbitrary-shape conducting
boundaries Arbitrary lattice takes MAD
input solenoids, dipoles, quads, sextupoles,
arbitrary fields, acceleration
Parallelized Benchmarked with intense
low-energy ion beam electron cloud POSINST
electron production models
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Work so far in 06 has been
benchmarking and LHC calculations
courtesy of Jean-Luc Vay, LBNL
Benchmarking on the LBNL High Current Experiment
LHC 100-m FODO cell
WARP-3D T 4.65?s
Electrons
200mA K
Beam ions hit end plate
Oscillations
Electrons bunching
5 beam bunches (yellow) electrons colored
according to intensity
with secondaries
without
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Proposed Program (07) - problems of
increasing complication
All are self-consistent (beam creating electrons
electrons affecting beam), and 3D unless noted
otherwise. Ecloud only in wiggler. Fully
nonlinear map elsewhere.
2D vs. 3D - 1 bunch, 1 pass through
wiggler then many bunches then offset
centroids ? start to benchmark 2D
results Head-tail instability - 1 bunch
through wiggler 1000 times. 3D. New
electrons each time. Effect of gaps and
resultant ecloud - bunch train with
gaps Electron cloud beam in wiggler -
single bunch train with ecloud from 3.
Follow for 1000 turns. (07-08?)
We will begin in the summer of 06
1.5 FTE in 07?
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Current Ecloud Activities _at_ Rostock
University Particle Tracking Program - MOEVE

• Based on the Poisson solver for space charge
  fields in a beam pipe of elliptical shape
• First version of the tracking routine
• Time integration of the particle equations with
  relativistic generalization of the
• equations
•  

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Current work - B-field rotation - Implementation
of external fields (longitudinal E-, transversal
B-fields) - Verification and comparison of the
tracking routine with existing programs -
Parallelization of the code - Definition of the
initial particle distribution possible use of
available bunch generation
programs To be done - Introduction the
slower electrons - Generation of the initial
particle distribution in the bunch - Graphical
presentation of the tracking