pbar transverse instability in main injector n.
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  1. Pbar Transverse Instabilityin Main Injector Ming-Jen Yang, Main Injector Jim Zagel, Instrumentation 04/12/2010

  2. 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.

  3. First data set, S7669x1 Output of MI FW integrator, integrating over four pbar bunches. Break-down occurred when signal was too large.

  4. 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.

  5. S7685x1 Pbarfrom RR, Vertical Flying Wire There is no apparent vertical plane oscillation at 8-GeV.

  6. 150 GeV pbar, S7706x1 Horizontal Flying Wire No apparent horizontal plane oscillation at 150 GeV.

  7. S7682x1, with PMT paddle replaced No break-down, but Oscillation is still as big as before.

  8. Reconstructed horizontal beam profile bunch# 1 bunch# 2 bunch# 4 bunch# 3 Peak integrated amplitude from each successive traces, for each bunch.

  9. Horizontal beam profile, as reported by FW bunch# 1 bunch# 2 bunch# 4 bunch# 3 Good agreement with the reconstructed profiles shown in previous slide.

  10. FFT on reconstructed profile, bunch #3 FFT spectrum from TBT BPM position at injection. 39136.4 Hz Tune = 39136.4 / 89815.3 = 0.4357 FFT spectrum of bunch#3 profile.

  11. 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.

  12. Adjusting MI chromaticity, nominal setting S7724, xfer #1 Chrom. H: -12 Chrom. V: -13 Oscillation: large FWH integrator signal Color legend: Outside plate Inside plate Difference MI horizontal wide-band pickup

  13. Adjusting MI chromaticity, -3 units S7724, xfer #1 Chrom. H: -15 Chrom. V: -16 Oscillation: smaller FWH integrator signal Legend: Signal - Outside plate Signal - inside plate Signal Difference MI horizontal wide-band pickup

  14. Adjusting MI chromaticity, -6 units S7724, xfer #1 Chrom. H: -18 Chrom. V: -19 Oscillation: invisible FWH integrator signal Legend: Signal - Outside plate Signal - inside plate Signal Difference MI horizontal wide-band pickup

  15. Adjusting MI chromaticity, -12 units S7724, xfer #1 Chrom. H: -24 Chrom. V: -25 Oscillation: invisible FWH integrator signal Legend: Signal - Outside plate Signal - inside plate Signal Difference MI horizontal wide-band pickup

  16. Signal of Wide-band, at injection Nearly perfect beam with no sign of beam distortion from RR.

  17. Wall Current Monitor signal, pbar bunch #1 Long profile: at injection Long profile: when flying wire flew

  18. Wall Current Monitor signal, pbar bunch #2 Long profile: at injection Long profile: when flying wire flew

  19. Wall Current Monitor signal, pbar bunch #3 Long profile: at injection Long profile: when flying wire flew

  20. Wall Current Monitor signal, pbar bunch #4 Long profile: at injection Long profile: when flying wire flew

  21. 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.