CESRTA Measurement of Electron Cloud Density by TE Wave and RFA

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CESRTA Measurement of Electron Cloud Density by
TE Wave and RFA

• Ben Carlson
• Grove City College
• Mentors Mark Palmer, John Sikora, and Mike
  Billing
• Cornell University
• Laboratory for Elementary-Particle Physics

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Electron Cloud Effect

• The Electron Cloud
• Synchrotron radiation ejects low energy
  photoelectrons from beam pipe
• Low energy electrons can be accelerated by
  positron bunches, causing ejection of secondary
  electrons

Schematic of EC build-up in a vacuum chamber, due
to photoemission and secondary emission
Courtesy F. Ruggiero
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Motivation

• ILC will require beams with very small volume in
  phase space
• Accomplished by sending the beam through a
  damping ring
• Synchrotron photons remove the transverse
  component of momentum
• Electron cloud effects are a known difficulty in
  regimes the proposed parameters of the ILC
• Electron cloud tends to induce coupled
  oscillations and destabilize the beam

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Techniques for Measuring EC

• Retarding Field Analyzers
• Measures electron flux in a localized region
• Application of a potential can be used to measure
  energy spectrum
• Transverse Electric Wave (TE Wave)
• Phase shift of carrier proportional to density of
  electron plasma
• Measures electron density over an extended region

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TE Wave Setup in the L3 Region
BPM48W
BPM49
BPM48E
Chicane
Q49
Q48E
Q48W
Solenoid
Spectrum Analyzer
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TE Wave Carrier With Sidebands
2GeV plot of dB vs frequency
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Comparison with RFA data
Courtesy Joe Calvey
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5GeV Chicane Scan 0.75mA/Bunch, 4ns spacing
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5GeV Chicane Scan 0.75mA/Bunch, 4ns spacing
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5GeV Chicane Scan 1mA/Bunch 4ns spacing
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Wigglers 5GeV 4ns spacing
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Conclusions Goals

• There is much to be explained regarding TE Wave
  measurements, though likely the TE Wave technique
  will not resolve the local effects and or
  artifacts seen in RFA data
• Try to determine spatial extent of TE Wave
  through modeling and measurements
• Compare extent with RFA method
• Determine whether resonance structure can be
  observed by TE Wave
• Evaluate cloud mitigation techniques for
  application in the ILC

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TE Wave Measurements
Induced phase modulation in the propagation of EM
waves through the beampipe
plasma frequency 2c(p?ere)1/2
Gaps in the fill pattern set the fundamental
modulation frequency (1st sideband). Higher order
components depend on the transient ecloud time
evolution during the gap passage.
Courtesy S. De Santis
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Wigglers 5GeV 4ns spacing
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Wigglers 5GeV 4ns spacing
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Splitter/Combiner Schematic Used for Both Drive
and Receiver
Lengths of legs are chosen to give 180 phase
shift at 1.7GHz