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Michigan B184 Update May 14, 2004 |
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1) Chambers passing CR test
a) Chamber passed CR test this week: EML3C07
b) Total number of chamber passed CR test at CERN: 16
2) Chambers in progress
EML3A15: CR test for almost two weeks
EMS4C16: CR test
EML3A07: Ready for CR test
EML4A05: T sensors and inplane system have been tested. Pressure
recycled and is recertifying the chamber. (one cracked
tubelet found)
EMS5C08: Epoxy done, are doing T sensor test and cabling.
EMS4C10: Epoxy half done
EMS5C02: Epoxy half done
3) Chambers in hospital EML4A05
4) Problems
a) CR test
For chamber EML3A15, we found "hot" channels with large area in the
same location of the hit map (first half of the hitmap, mostly
corresponding to mezz card ID with odd numbers. We replaced mezz
card 1,3,5 and hot channnels stayed. We then measured dark current
of single tubes for all corresponding hot channels, they are all
normal.
This is happenning to EMS4C16 too. and now is happening to EML3C07
when we use the DAQ system that was used for EML3A15.
The detailed situation can be discussed at the phone meeting.
I myself feel this is not a problem of the chamber itself, but
something to do with the DAQ system (DAQ system includes trigger in
my definition). Something must happened to the DAQ system (software
or hardware?).
If this problem is not solved in time, we will have to stop moving
ahead since we have no space to open more chambers.
Another unfortunate thing is that the two chambers stuck in the CR
test are the ones I planeed to empty space for UW. I will have to
deal it urgently next Monday.
So, strong measures are called for, and definitely needed, to
overcome the current bottleneck.
b) Tubelets with crack
Chamber EML4A05 has worse long leak rate (2.07 mbar/day) for ML2. We
added the gas to it to 3 bar. The next morning the pressure had
dropped to only a few psi, indicating a huge leak. This leak was
found to be from a tubelet with epoxy. Appearently the crack was
further opened up by presurizing the chamber. A bubbling test
showed two leaks around the bends (I saw one from top since I was
holding the tubelet and Reza saw two from side).
This is probably the most worrysome issue. Let's cross our fingers
and hope we won't find more. On the other hand, we should pay great
attention to any chamber with a bad long term leak rate.
c) On EML3A07 chamber, we found 6 tubes with high dark current. The
dark current ranges from 100-800 nA at 3.4kV. By applying -HV=2.5 to
3.2 kV we cured 5 of them. however one tube cannot be cured by
-HV. It tripped while one increase -HV to 3.2 kV.
Also the tube with larger resistence found by Rudi (and marked by
Rudi on the spacer frame) is on this chamber. So far the dark
current for this tube is normal (we didn't re-measure the resistence
before closing FCS, unfortunately. I though about it but then was
interrupted).
5) Other issues
a) I wish that any one who takes any parts and tools from blgd 184
could tell us so that we could register it. Except tracking parts,
we also want to avoid spending time to search tools which had been
taken away.
b) I once more remind that we all to pay attention to safety
issue. we don't want anyone to be hurt here at CERN, and don't want
our chambers to be damaged because of our careless. so please remind
each other while working, walking in blgd 184.
Zhenngguo Zhao