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BPMs period 13-14 Fast BPM use on ALICE

For most up-to-date summary of all 2012 BPM work go to \dlfiles03ALICEAnalysisPeriod 14 dataAP_period13and14eports sourcefiles which contains all the information in these slides. . BPMs period 13-14 Fast BPM use on ALICE. Background.

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BPMs period 13-14 Fast BPM use on ALICE

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  1. For most up-to-date summary of all 2012 BPM work go to \\dlfiles03\ALICE\Analysis\Period 14 data\AP_period13and14\reports\sourcefileswhich contains all the information in these slides.

  2. BPMs period 13-14Fast BPM use on ALICE

  3. Background • Fast BPM electronics originally designed for EMMA single bunch turn-by-turn orbit measurement (EMMA turns ~ 19 MHz) • Had been tested in 2011 on ALICE for bunch-by-bunch measurement (16 MHz) by Alex and IanK (see supplementary slides). It worked! • Apparatus exists for use of 5 simultaneous ALICE BPMs

  4. General BPM Projects • Bunch-by-bunch position and charge variation (transients, ripples) etc • Train-by-train position measurement • Inferred bunch/train energy variation • Beam based calibration • AR1 beam orbit and magnet misalignment • Dispersion (1st and 2nd order) measurement

  5. Chronology of BPM work • #3091, 16 Aug 2012. First quick look at fast AR1-BPM measurements, observation of transients and ripples • #3121-3123, 14-15 Sep. First look ‘in anger’ at AR1-BPM measurements, varying AR1-quads, PID in-out. During ALICE bunch charge problems. Data was presented at IBIC 2012 for first analysis of frequency content. • #3133, 3136, 3141, 17-23 Sep. More ripple observations, dispersion measurement, train by train measurement, alignment • #3168-3169, 06 Oct. More alignment data. • #3191, 14 Oct. Injector fast BPM measurement. AR1 dispersion vs sextupole

  6. Bunch to Bunch Variations and Transients

  7. Bunch-to-bunch variations • Measurements have shown a very rich picture of non-negligible ripples and transients in position and charge on the BPMs • These features are not always 100% clear, and have potentially many causes, possibly inter-playing with each other • Real position variation in the bunches caused by magnet ripple, HOM in cavities and elsewhere in machine. • Real energy variation caused by beam loading/RF performance • “Fake ripple” noise/electrical interference in the BPM system • Non-linear response of BPMS to charge/position • Try to identify and find cause of each feature.

  8. BPM position low frequency (100 kHz and lower) ripple • This is the most ‘obvious’ ripple since it is most easily observed by eye. • In the first look at AR1-BPMs, bunch-by-bunch data low frequency ripples, with a prominent peak at ~ 100 kHz • It’s appearance in x and y does vary. Sometimes very strong and clear, sometimes not, depending on set-up used and BPM in question . Usually stronger in x than y, which lead to dipole ripple (switched mode PSU) as first suspect. • It was also seen in injector BPMs upstream of any ALICE dipole • Is it seen on INJ-BPM-01? • This is ~100 KHz is NOT seen on the raw button voltages. It is NOT seen on the charge or FCUP signal. Does this suggest it’s cause CANNOT be EM interference? • Some of the low frequency content seen in the fourier transform is affected by the transients (remove the transient before fourier analysis to check this) occasionally this transient can enhance the 100 kHZ amplitude in fourier analysis • What parameters enhance/supress? Certainly focussing can, beam energy? 3121 AR1-BPM-03 3133 AR1-BPM-03 3133 AR1-BPM-04 3191 INJ-BPM-03

  9. BPM position fast frequency (6 MHz) ripple • Sometimes it’s as big, or bigger, than the, 10 kHz ripple (in terms of fourier amplitude).

  10. Bunch Charge Variations (all frequencies) • Transient ALWAYS presentin the charge • ~50-60 kHZ ripple (not seen in x, y - might be laser power variation bunch by bunch) • 300 kHz ripple observable • 6 MHz there too. • In injector, it mirrors exactly the y-position variation. • 6 MHz is seen not only in BPM charge measurement but also in faraday cup charge measurement.

  11. First Shifts #3091-#3123 • Initial shifts #3091, #3121-3123 were used for looking at transients, droop, and ripple. • But the shifts above were problematic for several reasons • Attenuation on buttons set differently to each other • Problems with bunch charge (scope set-up problems) • However, despite problems ripples and transient evident, as in 2011. • Much of the data on these shifts is doubtful because of the problems. A separate ppt for these files … • \\Dlfiles03\alice\Analysis\Period 14 data\AP_period13and14\BPM\bpms3091-3123.pptx • … However, some of this data was valid (attenuation set correctly) and was used for input to IBIC 2012 paper.

  12. #3121 Observations 16 MHz, 100 us (1600 bunch) trains, 30 pC Lattice from a THz-like set-up AR1 probably not closed … (strong-ish AR1Q1/4=2.22 A) Knowledge of beta functions poor/non-existent. mean values subtracted

  13. #3121 Observations • General observations, from a single shot: • bunch to bunch position variation; larger in x than y • various ripples seen on x, y, sum_V • initial “transient”, always on sum_V, sometimes on x, y. • The first observation might be naively expected, since any bunch energy variation would show in x but not y • But since beta functions so poorly understood, not possible to confirm this.

  14. #3121 Analysis. A very rich pictures of ripples, for IBIC 2012! • This data was the basic for the IBIC paper • Fourier-analysed the various frequency components • In x and y • Biggest feature is a ~ 100 kHz oscillation (170 bunches, 10 us) oscillation. Magnet ripple? • Other peaks in the 20-200 kHz range not exactly the same in x and y • Smaller ~300 kHz and 6 MHz signal on both and x and y. Hard to see the 300 kHz on the x,y plots. • In sum_voltage signal • 60-80 kHz signal. Laser pulse power variation? • 300 kHz quite visible on the sum_V. DC-DC converter? • 6 MHz as in x,y • So the biggest effects are the ~100 kHz ripple seen on x,y, and the ~ 60 KHz ripple on charge. I would suggest these are the highest priority to investigate.

  15. AP ‘block’ #3133, 3136, 3141, Week 17th 23rd September • Attenuation set correctly, charge 50-60 pC, 16 MHz • AR1-BPM-01, 03, 04, 05 • Check the x,y sign convention • Varying AR1-Q1-4 to try and generate high dispersion on 1 or more bpms to look for energy transients on trains. • 150-200, 100 kHz bunch oscillation seen very obviously in both x and y, on all BPMs • And similar amplitude in x on BPM-01 as BPM-05, suggesting this is not an energy oscillation • Identical oscillation on x and y on BPM-03. • Able to manipulate amplitude of y amplitude on BPM-05 by ST1-Q2

  16. #3133 • See \\Dlfiles03\alice\Analysis\Period 14 data\AP_period13and14\BPM\3133\3133.ppt • Struck by how regular the oscillation was compared to earlier shifts

  17. #3136 • ~1/2 a shift after FELIS/SNOM problems • Not much intra-train studies on this shift • Trying to measure dispersion, crudely, on AR1-BPM-05 by varying beam energy, and study how AR1-SEXT-01 affects the dispersion here (ideally, it shouldn’t affect dispersion). • Get some decent agreement between theory and measurement • Also can see the T166 component quite easily

  18. #3141 • Some software tweaks for automatic dispersion measurements • Changed beam energy to observe effect on ripple. 100 kHz (and lower freq) enhanced significantly by reducing the energy. • Higher order dispersion T166 observations • Measuring dispersion with single bunch vswhole_train_mean doesn’t make much difference • More detailed effect of sextupole vs. bpm-05 dispersion. • AR1-quad alignment data. • Recording many (1000) trains for train-to-train jitter measurements.

  19. #3168 #3169 6th October 2012. • Strange instability seen on ST2-BPM-03, 1 every 30 refreshes • Alignment data again.

  20. Summary of 2011 Tests • See \\dlfiles03\apsv4\Astec\Projects\ALICE\ALICE_Physics_Meeting\2011_09_20 • Some Key Points • Basic BPM resolution/noise is 20-30 um. • Initial train transient seen over 50 bunchers (~5 us) • Ripples seen at different frequencies. • horizontal: • period of (150 to 200) bunches, (80 to 110)kHz, two kinds: a single triangle wave for bunches 100 to 600 and a regular sine-like oscillation for bunches 600 to 1600, where the amplitude is (40 to 60)um; • period about <70 bunches, >230kHz, for bunches 100 to 600, amplitude (20 to 30)um; • vertical: • oscillations for 100 to 600 bunches are similar to that in the horizontal plane; • practically no oscillation of the second kind.

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