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User name jroche/jianglai
Log entry time 02:12:38 on December 6,2002
Entry number 53147
This entry is a followup to: 6689
Followups:
keyword=HV troubles, flaky CFD connectors,etc
We tried to take 1 hr fastbus run with 20uA, HV fullgain setting. Could not turn
on the HVs. Called Kaz and reset the magnet power supply current alarm. Still
didn't work. I (jianglai) and Louis went upstairs and discovered both "snipers"
had red light. Looked like the left sniper wasn't connected to anything. The red
LED on the right "sniper" indicated detector 6-16 had gone bad. Reset the
"snipers".
Reduced the current to 5uA. Full gain. HV tripped again. Same problem. Reset
Herbert's sniper again. Switched to reduced gain. HV tripped again. Asked for beam
off. Was able to turn HV back on @ 2uA.
We kept running at 2uA with reduced gain, fastbus-30Hz interleaved running mode.
Seemed like detector 3-02, 3-10, 4-16, 8-16 didn't show up any MT TDCs hits and
some of the CFD TDC hits are missing.
Julie came in and we went upstairs to check detector channels 3-02 and 3-10. PMT
signals looked good -- 400 mV signal size. Checked ADC spectra of these
PMTs, looked OK. So Julie suspected something was wrong with the connector
--- from the splitter to CFD. Replugged it and everything was back on track!
For the missing hits in 4-16 and 8-16, we recycled the corresponding HV crates.
Somehow HV tripped again during the recycling. The error light on the sniper
seemed indicating 6-16 went wrong again.
Louis and Julie discovered that the "6-16" channels on the left "sniper" was
actually connected to 4-16. Maybe that caused trouble? Anyway, reset the
sniper and restarted the HVs.
With reduced gain, we raised the beam current to 5uA, then 10uA. At 10 uA
beam, we measured the French base anode current.
2-04: 5uA
4-04: 5uA
4-16: 16uA
8-04: 5.5uA
8-16: 18uA
Comparable with previous measurement.
Raised HV to 15uA, then 20uA. HVs looked happy. I (jianglai) am really confused
why it kept tripping when I tried to run at 2 and 5 uA. But there was a peroid that
the beam position was very unstable (Herbert's looked OK though) and maybe I
just got bad luck.
Then we went to reduced gain. 2uA then 5uA beam. Everything was stable.
Before Julie went home, she left this note. Klaus and her measured I_ano with
reduced gain (elog 6689). 7-16 had 40uA @ 16uA beam.
So with full gain at 20 uA, I_ano of detector 7-16 would be:
I_ano = 40uA*4*(20uA/16uA) ~ 200 uA! So we need to reset the sniper threshold
before we go to higher beam current with full gain.