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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

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Cesrta measurement of electron cloud density by te wave and rfa

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
Electron Cloud Effect RFA

  • 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
Motivation RFA

  • 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
Techniques for Measuring EC RFA

  • 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


TE Wave Setup in the L3 Region RFA

BPM48W

BPM49

BPM48E

Chicane

Q48W

Q49

Q48E

Solenoid

Spectrum

Analyzer


Te wave carrier with sidebands
TE Wave Carrier With Sidebands RFA

2GeV plot of dB vs frequency

REU Talk


Comparison with rfa data
Comparison with RFA data RFA

Courtesy: Joe Calvey






Conclusions goals
Conclusions & Goals RFA

  • 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


Te wave measurements

Beampipe RFA

EM wave

Low-energy electrons

Phase velocitychangesin the ec region

frev/Ntrain

Positron current

E-Cloud Density

Relative phase shift

TE Wave Measurements

Induced phase modulation in the propagation of EM waves through the beampipe

Positron bunch train

plasma frequency

2c(πere)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]




Splitter/Combiner Schematic RFA

Used for Both Drive and Receiver

Lengths of legs are chosen to give

180 phase shift at 1.7GHz


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