Run Condition:
No B-field
helium:isobutane (70:30)
Wire target at 0.8 mm
After turning off the BLAST power, we got the beam around noon
and tuned the wire target positon so that the data rate is around
30 Hz and beam life time is around 5 to 10 minutes.
There seems no space-charge effect with the current gas mixture.
We did not notice that the signal to noise ratio in TDC distribution
change over time nor sense wire current growing over time. However,
the ratio decreased (increased) when the wire target was moved closer
to (or away from) the center of the beam. We also noticed that the
ratio for the right sector is three to four times better than that
for the left sector. I think the lead shield in the right sector
is definitely helping to get rid of showers and x-rays, which causes
space-charge effect.
This morning I had to raised the operating voltage by 100 V to
get the chamber efficient. If the gas mixture is not fully flushed
yet, we might have to raise the operating voltage even higher tomorrow.
There are two boxes (one from each sector) draws more than 15 microamp.
I lowered the operating voltage on these two boxes by 200 V.
All other boxes draw less than 0.5 microamp.
-T
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