Using Tune Shifts to Evaluate Electron Cloud Effects on Beam Dynamics at CesrTA
CESRTA Measurement of Electron Cloud Density by TE Wave and RFA
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Transcript of 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 CarlsonGrove 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
June 19, 2009 REU Talk 2
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 April 22, 2023 Cornell LEPP Template 3
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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
April 22, 2023 Cornell LEPP Template 4
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Chicane Q49
BPM48W BPM49 BPM48E
TE Wave Setup in the L3 Region
Solenoid
SpectrumAnalyzer
Q48EQ48W
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TE Wave Carrier With Sidebands
June 19. 2009 REU Talk 6
2GeV plot of dB vs frequency
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Comparison with RFA data
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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
June REU Talk 9
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5GeV Chicane Scan 1mA/Bunch 4ns spacing
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Wigglers 5GeV 4ns spacing
June 19, 2009 REU Talk 11
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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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Low-energy electrons
Beampipe
EM wave
Phase velocity changes in the ec region
k2 2 c
2 p2
c2
plasma frequency2c(πere)1/2
Induced phase modulation in the propagation of EM waves through the beampipe
Positron current
E-Cloud Density
Relative phase shift
frev/Ntrain
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.
Gap
Positron bunch train
Cesr ring
EM Wave
TE Wave Measurements
[Courtesy S. De Santis]
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Wigglers 5GeV 4ns spacing
June 19, 2009 REU Talk 14
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Wigglers 5GeV 4ns spacing
June 19, 2009 REU Talk 15
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Beam Pipe Response when Driving at 0E and Receiving at Various Detectors
-70
-60
-50
-40
-30
-20
-10
0
10
1.72E+09 1.73E+09 1.74E+09 1.75E+09 1.76E+09 1.77E+09 1.78E+09 1.79E+09 1.80E+09
Frequency
Re
ce
ive
d S
ign
al
(dB
m)
0E to 0E
0E to 0W
0E to 1E
0E to 1W
0E to 2E
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Splitter/Combiner SchematicUsed for Both Drive and Receiver
Lengths of legs are chosen to give180 phase shift at 1.7GHz