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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

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 photoemissionand secondary emission

[Courtesy F. Ruggiero]

REU Talk

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

Cornell LEPP Template

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

Cornell LEPP Template

Comparison with RFA data

Courtesy: Joe Calvey

Wigglers 5GeV 4ns spacing

REU Talk

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

EM wave

Low-energy electrons

Phase velocitychangesin the ec region

frev/Ntrain

Positron current

E-Cloud Density

Relative phase shift

TE Wave MeasurementsInduced phase modulation in the propagation of EM waves through the beampipe

Positron bunch train

plasma frequency

2c(πere)1/2

Cesr ring

Gap

EM Wave

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]

Wigglers 5GeV 4ns spacing

REU Talk

Wigglers 5GeV 4ns spacing

REU Talk

Used for Both Drive and Receiver

Lengths of legs are chosen to give

180 phase shift at 1.7GHz

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