1. 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

2. 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]
June 19, 2009
REU Talk

3. ILC will require beams with very small volume in phase space
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
November 9, 2018
Cornell LEPP Template

4. 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
November 9, 2018
Cornell LEPP Template

5. BPM48W BPM49 BPM48E Chicane Spectrum Analyzer
TE Wave Setup in the L3 Region
BPM48W
BPM49
BPM48E
Chicane
Q48W
Q49
Q48E
Solenoid
Spectrum
Analyzer

6. TE Wave Carrier With Sidebands
2GeV plot of dB vs frequency
June
REU Talk

7. Comparison with RFA data
Courtesy: Joe Calvey

8. 5GeV Chicane Scan 0.75mA/Bunch, 4ns spacing

9. 5GeV Chicane Scan 0.75mA/Bunch, 4ns spacing
June
REU Talk

10. 5GeV Chicane Scan 1mA/Bunch 4ns spacing

11. Wigglers 5GeV 4ns spacing
June 19, 2009
REU Talk

12. Determine whether resonance structure can be observed by TE Wave
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

13. TE Wave Measurements
Induced phase modulation in the propagation of EM waves through the beampipe
Low-energy electrons
Beampipe
EM wave
Phase velocity changes in the ec region
plasma frequency
2c(πere)1/2
Positron current
E-Cloud Density
Relative phase shift
frev/Ntrain
Gap
Positron bunch train
Cesr ring
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]

14. Wigglers 5GeV 4ns spacing
June 19, 2009
REU Talk

15. Wigglers 5GeV 4ns spacing
June 19, 2009
REU Talk

17. Splitter/Combiner Schematic Used for Both Drive and Receiver
Lengths of legs are chosen to give
180 phase shift at 1.7GHz