As Rory will be out of town up to next Tuesday, I volunteered to assume the coordination
for the remaining commissioning with photon beam.
Going through last weeks data, the key issue to resolve is to get the rate of accidental
triggers down by about a factor of at least 8. Indeed, runs taken at 5 nA with collimators
in and the full g1 photon trigger (ALLTOF_ASYNC.MOR.ST) had a trigger rate of 3 kHZ, whereas
this rate was 60 Hz at 0.5 nA. That means we are far from taking data at 10^7 photons/s,
which corresponds to 10 nA, because a reasonable DAQ rate is 700 to 800 Hz.
How can we gain:
1/ reduce the width of the MOR.ST coincidence to 12 ns (instead of about 25 ns now).
This requires adjusting the T counter cable length to within 1 ns.
2/ reduce the width of the TOF at level 1 as much as possible, without biasing the trigger.
That needs further timing studies.
3/ Most importantly, shield against the source of background we see in TOF sector 5 and 6.
P.S.: I have posted some DC and TOF population spectra from these runs at
http://www.jlab.org/~marchand/commissioning
Claude Marchand.