electron cloud modeling for cesrta daniel carmody mentors: levi schächter, david rubin august 8th,...
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Electron Cloud Modeling for CesrTA
Daniel CarmodyMentors: Levi Schächter, David Rubin
August 8th, 2007
8/8/2007 Daniel Carmody 2
Overview
• Topic\Theory
• Goals
• Methods
• Future Work
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The ILC - CESR’s role
CesrTA proposed to investigate factors that limit the performance of the ILC
http://www.interactions.org/imagebank/search_detail.php?image_no=OT0052
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The Electron Cloud Effect
Beam particles emit synchrotron radiation
Synchrotron radiation generates photoelectrons
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The Electron Cloud Effect
Positrons travel in bunches/trains
Bunches generate a cloud of electrons
•build-up
•equilibrium
•decay
lifetime
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Measurements
April 2007
Tune extrapolated from BPM measurements
Approximate decay time of 170ns
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The Issue
Characterize the development and decay of the electron cloud in CESR:
magnetic fields
beam parameters
vacuum chamber design
primary/secondary electron emission yields
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The ECloud Program
Models a single magnetic chamber of the accelerator
Hundreds of macro-particles representing billions of electrons
Carry a variable amount of charge
More introduced every bunch passage
Charge may change when particle reflects off wall
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ECloud Input/Output
QuickTimeᆰ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Variables•bunch grouping•bunch current•bunch separation•photoelectron yield•secondary emission
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The Analytic Model
•Each bunch contributes a number of new electrons to the cloud (∆)
•The cloud is reabsorbed by the wall according to an
exponential decay law (lifetime, )
ν 0
Nb
1
D h t TÎ ½ e
t TÎ ½
t
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Matching the Data
y tν 0
Nb
1
D h t TÎ ½ e
t TÎ ½
t
f t isdata
E t , Di
f tiy t
i, t ,D
2
i
f ti
2
D t i
f ti
i ν 0
Nb
1
h tiTÎ ½ e
t TÎ ½
t
¶E
¶D0
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Mathematica Modeling
time
dens
ity
lifetime
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ECloud Modeling
10 bunches 14ns bunch spacing2.085 GeV dipole magnetic field
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Mathematica Fitting
Time (s)
Density
(particles/m3)
Varying:
PEEFF = Primary Photoemission Yield
REFL = Photoelectron Distribution
SEY = Secondary Emission Yield
B Field = Magnetic Field Chamber
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Parameter Search
Job Name Field Strength (gauss) SEY PEEFF Lifetime (ns) REFL
job51 800 1.4 0.01 143 80
job52 800 1.6 0.01 174 80
job53 800 1.8 0.01 240 80
job54 800 1.8 0.01 212 40
What are realistic values for parameters to have?
materials research
tabletop experiments
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Issues
Many parameters many possible sets that fit
Which most accurately represents the situation?
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ibeam = 0 Ibeam = 1
EnergySpread
AverageEnergy
Ene
rgy
(eV
)
179ns 204ns
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The Best Fit
Many parameters many possible sets that fit
Which most accurately represents the situation?
Job Name Field Strength (gauss) SEY PEEFF Lifetime (ns)
job52 800 1.6 0.01 174
job65 800 1.6 0.01 204
job67 800 1.5 0.01 168
ibeam=1
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Where does it go from here?
•See what parameters can be changed to help mitigate the ECE
•Determine the instability thresholds
•Implement diagnostic tools for more direct measurement of EC
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Sources
[1] K. Harkay, Prepared for 31st ICFA Beam Dynamics Workshop: Electron Cloud Effects (ECLOUD04), Napa, California, 19-23 Apr 2004
[2] M. A. Palmer, R. W. Helms, D. L. Rubin, D. Sagan, J. T. Urban and M. Ehrlichman, Prepared for European Particle Accelerator Conference (EPAC 06), Edinburgh, Scotland, 26-30 Jun 2006
[3] G. Rumolo and F. Zimmermann, CERN-SL-2001-067-AP-D
[4] ”Electron Cloud in the LHC” web page, http://ab-abp-rlc.web.cern.ch/ab-abp-rlc-ecloud/
[5] G. Rumolo and F. Zimmermann, CERN-SL-Note-2002-016 (AP)
[6] D. Schulte and F. Zimmermann, Proc. 31st ICFA Advanced Beam Dynamics Workshop on Electron-Cloud Effects ECLOUD04, 2004