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

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]

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

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

Chicane Q49

BPM48W BPM49 BPM48E

TE Wave Setup in the L3 Region

Solenoid

SpectrumAnalyzer

Q48EQ48W

TE Wave Carrier With Sidebands

June 19. 2009 REU Talk 6

2GeV plot of dB vs frequency

Comparison with RFA data

7

Courtesy: Joe Calvey

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

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

June REU Talk 9

5GeV Chicane Scan 1mA/Bunch 4ns spacing

10

Wigglers 5GeV 4ns spacing

June 19, 2009 REU Talk 11

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

12

13

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]

Wigglers 5GeV 4ns spacing

June 19, 2009 REU Talk 14

Wigglers 5GeV 4ns spacing

June 19, 2009 REU Talk 15

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

Splitter/Combiner SchematicUsed for Both Drive and Receiver

Lengths of legs are chosen to give180 phase shift at 1.7GHz