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User name A. Camsonne
Log entry time 21:48:47 on November 11, 2009
Entry number 299023
We got the expert of MCC to check the background rates.
Closing the slits to have good clean beam at 10 uA yielded a background
rate of about 150 Hz/uA at 1650 V.
Reza tweaked the injector to find the parameters to improve the
background and get the rates low at high current. It seems the photon
Compton rates are pretty gang (?) phase of the North Linac, the
prebuncher is also crucial at high current ( running without indeed it
makes rate really bad ).
We made an aperture scan in X and a vertical scan.
The signal could be clearly seen at 1600 V with a gain of 1, though the
signal seemed to disappear at high current mostly due of increase and
background but I wonder if the PMT functions correctly at high current
since it draws a significant amount of current. One oddity was we could
not see the signal any more when going back to 10 uA so I turned the
detector off in case it needed to recover. It seemed to work at 2 uA when
the beam was resumed. I asked to Megan to check the linearity of the PMT
with the LED with beam to check for any gain change due to high current.
It seems the detector sees a lot of low energy background so that might
change the gain. So additionnal shielding and fixing the bad vacuum might
be the way to go.
More detailed informations in Arne's
A lot of progress since we could actually see the signal and optimize it
but still some work needed since it seems the background increases at 80 uA.