Operators: kohlm tavi ----
Beam offset studies with collimator and empty target.
Setting 1:
Runs 2985 2986 2988 2989 2990 2991 2992 = +1mm horizontal offset.
Charge approx. 280C beamgated.
Setting 2:
Runs 2995 2996 = -1mm horizontal offset
Runs are lrn'd and charged.C'd.
The slits were optimized for each setting.
While the +1mm horizontal setting 1 was very quiet at >20min lifetime,
the latter -1mm setting 2 provided only 5min lifetime. The slit positions and BQM rates were
setting 1 setting 2
slit / BQM slit / BQM
L -3 U 52 L 0 U 160
R 14 L 15 R 12 L 32
T -0.6 D 12 T 0.6 D 46
B -7.5 R 7 B -8 R 39
In setting 2 R24 tripped frequently about every 5 min.
Event rates:
Setting 1 80mA/20min Setting 2 80mA/5min
PHYS BPHY PHYS BPHY
0 400 150 0 4000 240
1 440 150 1 2000 80
2 400 180 2 3000 200
Setting 1 is very comparable to nominal setting at h/v=0/0. However, offset to the opposite side gives tremendous rise of event rate, we are scratching the collimator.
Prior to setting 1 it was attempted to drive a setting at h=+2mm, which was interrupted because of the too high rates and frequent tripoffs, in fact a very similar scenario like setting 2.
As already 1 mm offset changes the (background) rate by a factor 10, I would recommend to increase the inner diameter of the collimator by 2mm.
Plan is to collect more data (if trip frequency does not increase) in setting 2 (ca. 40C per run, i.e. 7 runs), then change to h=0 and v=+1mm, and v=-1mm later. Collect about 250-300C in each setting.
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