Failure analysis at BEPCII J. Xing, J.S. Cao IHEP ARW2017, Versailles, 17.10.2017
Outline Introduction Failure analysis tools Some examples Summary
Introduction BEPCII —An upgrade project of Beijing Electron Positron Collider —A double-ring factory-like machine —Deliver beams to both HEP & SR Linac Storage ring BESIII BSRF
NEXT : TOP-OFF(Collision) Design Goals of BEPCII Collision(achieved) Beam energy range 1-2.1 GeV(2.3GeV) Optimized beam energy 1.89 GeV Luminosity 1×1033 cm-2s-1 @1.89 GeV(April 5, 2016) Full energy injection 1-1.89 GeV(2.3GeV) Synchrotron radiation(TOP-UP) Beam energy 2.5 GeV Beam current 250 mA Keep the existing beam lines unchanged NEXT : TOP-OFF(Collision) 4
Operating Schedules & Management Mechanism Total 7344hours ( >7000hours/year) Routine maintenance on Tuesday (68hrs). Acc. Daily meeting(Collision). Weekly meeting(SR). BEPC National Laboratory (Acc. & HEP & SR & others) Weekly meeting(Monday) 5
Availability of BEPCII(SR) Average 96% Goal >98% Failure rate of BEPCII(Collision) Average 8% Goal <5%
Failure analysis tools 16-channel oscilloscope Beam trip diagnostic system 7
16-channel oscilloscope A 16 channels oscilloscope is used in RF system to record the beam, accelerating voltage, RF power, LLRF control loop related signals and so on; A preliminary tripping reason analysis can be achieved by distinguishing the time sequences and variation tendencies of the signals. 8
Beam trip diagnostic system (base on bunch-by-bunch system) Bunch-by-bunch and turn-by-turn Time domain and frequency domain Tune in three dimensions Beam Current：last 30000 turn Beam current in the end：800 turn Bunch current Bunch RMS/mm Position X FFT X Position Y FFT Y ① ③ ⑤ ⑦ ② ④ ⑥ ⑧
Some examples Beam trip statistics Almost all the tripping can be distinguished as the following types: RF system (including suspected SC cavity trip) beam instability (failure of the feedback system) power supply system Other hardware systems trip resulted in beam lost, such as control system, magnet system, cryogenic system and so on. Beam trip statistics 10
RF trip voltage The beam longitudinal oscillation beam 11
Multipacting or stress jump? RF “f-phase” trip RF “f-phase” trip occurred frequently when the electron beam >700mA during the past year. RF forward power RF reserved power RF voltage RF phase Beam f-phase jump Loading angle Piezo Driver The loading angle was found jumped sometimes at the end of May 2017, the beam lost when the frequency control loop can not catch up. Multipacting or stress jump? 12
This SC Cavity has just been changed as the f-phase trip is one of the important reasons. 13
Beam instability Feedback system: Phase shift Bunch current Not uniform Transvers oscillation Tune X Feedback system: Phase shift the damage of the power amplifier Bandwidth limited (high current with more bunches) Undergoing: digital & new feedback kicker
Power off with Alarm: easy to find Power supply Power off with Alarm: easy to find Unstable: difficult to find sometimes It occued a dozen times that the positron and electron were tripped at the same time in the January 2017 and must be caused by the unstable state of the public magnet power supplies (Q1A or ISPB). 15
Check the Q1A power output through the inspection system. Not matching with ISPB Beam trip by ISPB Check the Q1A power output through the inspection system. See nothing: slow system vs. fast change 10ms.
Solution: tighten the power supply terminal block! Knob Q1A (I -15A) Solution: tighten the power supply terminal block!
Summary Keeping high availability during a long operation period is quite challenging. The 16-channel oscilloscope and the beam trip diagnostic system are powerful failure analysis tools. We are training the operators to have capability to use the failure analysis tools.
Thanks for your attentions !