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User name D. Lhuillier
Log entry time 16:23:08 on October14,2005
Entry number 156800
Followups:
keyword=Compton background
Compton counting rates are back to very low level (see picture below). Expected Signal/Background ratio is above 10.
The high rate in the photon detector we were trying to reduce yesterday night (6kHz/uA) was due to light pulses sent by a diode we usually use for checks or calibration. This diode was somehow turned on without notice and I forgot to check it yesterday.
When the electron beam was off the compton photon rate displayed at MCC was 0 although the diode was still firing. This is because we were looking at rates normalized to beam current and when the current drops below a given cut the rates are set to 0...
Everything makes sense now, the beam tune was actually good as soon as we reduced the electron background and we wasted 4h of beam time trying to kill the diode signal with beam optics optimization.
Sorry about that.