PEP-II Run 4 Post Mortem Beam Position Monitors August 4, 2004 Steve Smith

8/04/04PEP-II Run 4 Postmortem Convert Remaining BPMs to 2D Readout Measure X & Y at every quad –Instead of X-only, Y-only Compensate for pin-cushion distortion due to duct. –Apparent X-Y coupling Build 65 more BPM “RINQ” processors. Requires staged installation of additional cable plant.

8/04/04PEP-II Run 4 Postmortem Automatic BPM Calibration Problem: BPM calibration (gains, pedestals) often became stale –Calibration requires no beam (since gap narrowed) –Could not re-calibrate since that would cause orbit jump –Avoid recalibration especially between fills. Solution: Automatically run calibration when beam goes away. –Compare new parameters with old –Update if changes within tolerance ( 200  m => 100  m) Remaining Problems: –BPMs gradually fall out of operation due to cuts –Must have operator-initiated calibration on at least weekly basis to recover. –Get jumps of up to 100 microns due to slow drifts in electronics –Must live with these if we want BPMs to maintain absolute orbit. –Or lose track of absolute orbit if don’t want L jumps

8/04/04PEP-II Run 4 Postmortem Position Algorithm Bug Found & Fixed Aug 2000: Successfully introduced new firmware to reduce position sensitivity to uncalibrated parameters Requires database change to calibration parameters Modified source doesn’t go into code management Nov. 2000: The next firmware revision undoes algorithm change –Restores problem previously fixed –database doesn’t match algorithm: introduces large errors for large beam position, Creates apparent coupling even at small beam excursions Easily fixed once found, but algorithm was wrong for substantial time.

8/04/04PEP-II Run 4 Postmortem Timing Bug Observed: –Flakey timing curves –Timing shifts on module change In RINQs S/N Built for last summer’s PR02 upgrade. Bug identified as wrong resistor loaded on vernier timing generator on RINQ All spares in lab fixed. Remaining modules will be fixed during shutdown –Will lead to one more round of timing shifts. –To be fixed at startup.

8/04/04PEP-II Run 4 Postmortem I & Q Swap RINQ Modules S/N > 200 have I&Q demodulator outputs swapped. Normal calibration doesn’t care Refined calibration does. Trying to fix in firmware. Should be easy but –Firmware tools seem flakey. –Will we be able to accomplish other bug fixes/upgrades?

8/04/04PEP-II Run 4 Postmortem BPM with Large Beam-Based Alignment Offset BBA shows several large quad-BPM offsets BPM PR had large ~10 mm y offset Quad checks out OK –Hall probe –Voltage drop /pole Swap BPM cables –Its not electronics Run BPM cables out –Scope, TDR –Spectrum analyzer –Voltmeter/ammeter BBA analysis problem found Looking at wrong BPM

8/04/04PEP-II Run 4 Postmortem New BBA Analysis BPM Xoff Xerr Yoff Yerr (mm) (mm) (mm) (mm) BPMS PR (QFBM5 ) BPMS PR (QFBM4 ) BPMS PR (QDBM3 ) BPMS PR (QFBM2 ) BPMS PR (QFBM1 ) BPMS PR (QFCX1R2) BPMS PR (QFCX1R1) BPMS PR (QF2R ) BPMS PR (QF2L ) BPMS PR (QFCX1L1) BPMS PR (QFCX1L2) BPMS PR (QFBM1L ) BPMS PR (QDBM2L ) BPMS PR (QDBM3L ) BPMS PR (QDBM4L ) BPMS PR (QFBM5L ) Three serious offenders to be investigated

8/04/04PEP-II Run 4 Postmortem Injection Line BPM History Original Implementation: Multiplex up to 8 injection line BPMs onto long cable into each linac processor. Early result: Injection feedback runs too slowly. First upgrade: Split signal into 4 processors –acquire all BPMs each shot. Problems: –Small signals Long cables Each BPM coupled to cable by -10 dB coupler. Then split off in -6 dB splitter. –Kicker noise Signal small Cable plant multiply connected to beampipe, cable tray.

8/04/04PEP-II Run 4 Postmortem Injection Upgrades Ran 3 new sets of BPM cables up tunnel. Signal strength improved by > 15 dB. Shorter long haul cables Not all of them traverse the kicker region Reduced ground-loop pickup Signal improved by ~ x 8 Noise reduced Installed in LER injection arc in February Operators are happy with performance Injection feedback now operational HER injection arc to upgrade this down.

8/04/04PEP-II Run 4 Postmortem BPM History Plots Identify “jumps” Flag discontinuities in beam or monitors Aids diagnosis PR Jump 1 hr after fill Returns on abort

8/04/04PEP-II Run 4 Postmortem More Improvements Module offset database –Module queried for bench calibration constants New operational modes: –Online/Maintenance/Checkout/Offline –Enable better diagnostics/checkout –Need Ops to promote BPMs from Checkout to Online more often

8/04/04PEP-II Run 4 Postmortem Some Improvements are Free: Position vs. Bunch Number Old bunch pattern (x3)  = 148  m  = 104  m (excluding Q4) Current bunch pattern: Every other bucket (pattern for which calibration is designed)  = 21  m

8/04/04PEP-II Run 4 Postmortem Beam Phase Turn-Turn Can we measure phase of injected bunches? Tune injected phase & energy. BPM processors acquire info every turn (but ignore it) Expected resolution: few degrees RF for 5% charge top-up bunch on top of full bunch. First data: BPM processor phase jitter limits resolution to ~5 o rms at 1 kHz offset frequency. Must fix to extract injected bunch phase.

8/04/04PEP-II Run 4 Postmortem Radiation Upsets in BPM Processors Found BPM processor memory frequently corrupted Concentrated in a few crates Radiation survey found high residual radiation on HER straight section to arc chamber transition adjacent to these crates. Apparently scraping beam here Plan: –Install lead & concrete shielding (done) –Plus polyethylene around crate (under study)

8/04/04PEP-II Run 4 Postmortem End of Straight 12

8/04/04PEP-II Run 4 Postmortem Concrete Added Around BPM Crate

8/04/04PEP-II Run 4 Postmortem Continuing Upgrades/Investigations BBA shows BPM/Quad inconsistency –3 BPMs in PR02 to be investigated Can we maintain RINQ code? Memory corruption –Radiation –Something else? Upgrade HER injection line BPMs Arc BPM => 476 MHz? Jumping BPMs? –Must address on case-by-case basis

8/04/04PEP-II Run 4 Postmortem Tough Problems Remain Slow drifts of electronics –Electronics designed to calibrate as needed –Now can only calibrate once or twice a day –Light-source like (narrowband) BPMs may be better suited for PEP’s present needs. Low bandwidth, simultaneous calibration Maintenance –Electronics are still in the tunnel –Diagnosis/repair of in-tunnel electronics sometimes requires multiple accesses Can take many weeks to identify/solve problem –if we didn’t guess right the first time and have to wait for 2 nd ROD to try again.