Pbar Transverse Instability in Main Injector

Pbar Transverse Instability

in Main Injector

Ming-Jen Yang, Main InjectorJim Zagel, Instrumentation

04/12/2010

Study

Initially motivated by Noisy in MI flying wire beam profile

- Changed PMT high voltage- Replaced PMT paddle in the tunnel- Noisy only on pbar from RR.

Installed RTD720 digitizer at MI10 Digitize monitor signal supplied by FW system

- Raw PMT signal- FW integrated loss signal.

Independent of FW front end - Turn-by-turn.- No decimation.

First data set, S7669x1

Output of MI FW integrator, integrating over four pbar bunches.Break-down occurred when signal was too large.

Acc. to RR transfer, for comparison

Scale of oscillation is quite a bit smaller.MI transverse plane damper are in use for this type of transfers.

S7685x1 Pbarfrom RR, Vertical Flying Wire

There is no apparent vertical plane oscillation at 8-GeV.

150 GeV pbar, S7706x1 Horizontal Flying Wire

No apparent horizontal plane oscillation at 150 GeV.

S7682x1, with PMT paddle replaced

No break-down, butOscillation is still as big as before.

Reconstructed horizontal beam profile

Peak integrated amplitude from each successive traces, for each bunch.

bunch# 1 bunch# 2

bunch# 3 bunch# 4

Horizontal beam profile, as reported by FW

bunch# 1 bunch# 2

bunch# 3 bunch# 4

Good agreement with the reconstructed profiles shown in previous slide.

FFT on reconstructed profile, bunch #3

FFT spectrum of bunch#3 profile.

FFT spectrum from TBT BPM position at injection.

39136.4 Hz

Tune = 39136.4 / 89815.3 = 0.4357

Observation

Hashing in the profile Result of betatron oscillation

- Give the same Tune as measured with TBT BPM. Bunch # 1

- Minimal oscillation.- Clean profile from both version.

Bunch #3 - Substantial oscillation.- Noisy FW profile.

Bunch #2 & #4- Comparison not as clear-cut.

Double peak feature- Caused by PMT break-down.- Disappeared with reduced high voltage.- FW profiles are similar to the reconstructed profiles.

Adjusting MI chromaticity, nominal setting

Color legend:Outside plateInside plateDifference

S7724, xfer #1 Chrom. H: -12Chrom. V: -13

MI horizontal wide-band pickup

Oscillation: large

FWH integrator signal

Adjusting MI chromaticity, -3 units

Legend:Signal - Outside plateSignal - inside plateSignal Difference




Oscillation: smaller






Oscillation: invisible

Signal of Wide-band, at injection

Nearly perfect beam with no sign of beam distortion from RR.

Wall Current Monitor signal, pbar bunch #1

Long profile: at injection Long profile: when flying wire flew

Summary

At injection- No visible beam profile distortion.- Neither longitudinal nor horizontal.

At the time when flying wire flew Horizontal plane

- Bunch #1 show the least amount of distortion.- Bunch #3 & #4 are the worst.- Profiles deteriorated, horizontal and longitudinal.

Vertical plane- None.

At 150 GeV- None.

Pbar from Accumulator to RR- Visible, but smaller, horizontal plane oscillation.- MI transverse damper is in used for these transfers.

Chromaticity damping- Effective.- Set chromaticity to -18 units, from nominal of -12.

Pbar Transverse Instability in Main Injector

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