Electron Cloud Modeling for CesrTA

Daniel CarmodyMentors: Levi Schächter, David Rubin

August 8th, 2007

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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