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User name Armstrong
Log entry time 13:07:08 on October 05, 2009
Entry number 293275
keyword=More on Compton problem and Hall A laser phase
Diancheng has worked with MCC and they have adjusted the Hall A laser
apparently the photon detector is happy again at 1800 V. Looks like 200
Hz with laser off,
870 Hz with it on. Having talks to MCC, it seems that they had indeed
made an adjustment
to the Prebuncher GSET at about the time we had the photon detector
problems. Apparently they
had noticed a tail on the synchrotron light monitor, and an increase in
the "beam interception"
on the Master Slit. Perhaps this adjustment was related to what caused
the high rate in
the photon detector. However, it seems to have been the wrong cure, since
the cure instead
was to adjust the Hall A laser phase (MCC tells me the photon detector
rate was somewhat
sensitive to the "Prebuncher GSET", but the cure that really worked was
the laser phase.
Apparently the *only* available diagnostic is the photon detector rate,
and the technique is
to turn Compton laser off, and empirically "tweak" the Hall A laser phase
and have MCC
watch the singles rate from the GSO photon detector.
Moral of the story: when photon background rate goes up (and GSO HV trips
with beam on)
ask MCC to tune Hall A laser phase.