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Michigan B184 Update March 26, 2004 |
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1) Chamber CR tested this week: EML4C09.
Total chamber CR tested: 4
2) chamber in progress:
EML3C03: Around 10 hot channels exist. Most of these hot channels
are related to settings from DB. We are flushing with
bottle gas and will take CR data to compare the drift
time.
EMS5C12: Recertified to 4 mbar/day, dark current tested, ready for
CR test.
EMS5A02: Vecco is used to recertify the chamber. We are still
certifying it. We may have serious problem on endplugs. see
the following "problem" part
EMS5A08: We are making up the epoxy. Q196 didn't find any leaks. will
use Vecco to certify it next week
3) Problems:
- Flaky SHH cards
As I reported some days ago, we find 6 SHH cards in one chamber
had very bad contact to the pin. after a few time unplug and plug the
cards, contact improved. in the CR test, one channel appeared to be
dead (in the beginning it was fine). we then decided to clean SHH card
pin with acetone by using the wash basin made by Curtis. it appeared
to be very effective.
We then decided to replace SHH cards for EML3C03 and EML4C09, which
were doing CR test. MECCA test show that the cleaned SHH cards have good
contact, no longer flaky. The procedure is:
1) Immerse SHH cards (socket) in the wash basin for about 5 minutes
2) Use electronic tooth brush (for kid) to brush the pins
One can see by eye lots of while material is brushed out of the
pin. By the way, the wash basin is a very good design. Simple and use
less acetone.
Today we mounted the washed SHH cards to the chamber and tested
continuity with MECCA. All easily past the test. NOT one dead or flaky
channel found.
I'm pretty confident that our method of cleaning SHH card work
well. And I think we do need to add this step to our integration and
test of the chamber.
- Hot channels
EML4C09 and EML3C03 chambers have been doing CR test for 7-10
days. hot channels still exist. I don't think we can do much for
them. We think most hot channels are due to the improper setting of
the mezz cards threshold from DB. Chamber themselves are pretty quiet
in terms of dark current. Experts's help is urgently needed.
If the CR test is continuously to be so, it will be the bottle neck
of our work. Of course, hot channel depends how one define it.
- The last but not the least, cracks and leaks
Comment from Jeff Gregory about the hot channels:
Just a comment on the noisy channels. They are not because of
"incorrect" settings. They are due to a limitation in the design on
the ASD. Thresholds are set for groups of 8 channels at a time, three
per mezzanine card. From the DB information, we set the threshold at
the median value of the 8 channels. If one of the channels is far
from the median, it will appear be 'noisy'.
This threshold difference is made more pronounced by the
relatively electrically noisy environment of building 184. There may
be something particular about the DAQ setup at building 184 that is
contributing to this, but it does not seem to be something internal to
the chambers.
We could use some value other than the median for setting the
thresholds. Moving all the thresholds 10mV farther from 0 will kill
the noise and make a very pretty profile, but it will also
significantly worsen resolution and I don't think it is called for.
I propose that for chamber commissioning, all hot channels should
be compared to the database. If the database lists a high offset for
those channels then they are ignored ("high" is relative but can be
determined quantitatively from the rest of the ASD). If it does not,
then the setup should be checked for problems (bad signal HH, etc).
This will avoid serious CR bottlenecks. Electronics scans are going
relatively smoothly now and so most chambers should pass with 1 day
spent running the electronics scan and 1 night of cosmic ray data.
Additional criteria from the electronics scan can also be defined.
Also, I will continue to search for external sources of noise when I
have a free chamber available for more than a day or two.
-Jeff.
EMS5A02:
This chamber has a long term leak rate of 2 mbar/day for both
multilayer for about 2 years. this value is higher, according my
experience. The leak rate is about 20 mbar/day with helium for 93
hours measurement. No leaks were found with Q196 (red caps were used
to the signal caps in order to be sensitive to the leaks). We (Alan
did it, I sampled some of them) used VECCO to "scan" all possible leak
spots. Surprisingly we found that the location of the endplugs alone
the tube end has leak rate around 5 x(10^-6 - 10^-5 ml/sec) for almost
ALL tubes. Some sector (tube with the same length appeared to have
high leak rate around 5x10^-5 ml/sec, some at 5 x 10^-6 level). I then
suspect that there might be cracks in that region which we cannot see,
or the structure of the material of these endplugs are so loose that
they appeared to be micro-cracks everywhere. This may be particularly
true when the endplugs under stress.
Incidently, Agostino came to bldg 184 right at a time when I mentioned
to Alan my own suspicions. Agostino told me that they found 5 endplugs
have cracks in such a region.
I am pretty sure one cannot explain such a high leak rate as from
diffusion.
If the leak stay at this level, it's not a big problem. I myself
believe that 10-20 mbar/day leak rate is good enough for muon
chambers, though we have been strictly shooting for reaching ATLAS
specification. The problem is if the leak rate increases as a function
of time, we then have a big trouble here simply we probably can do
nothing for so many tubes in this location.
Can any one trace the history of this chamber? it's the MIC004 chamber.
It's again a week fighting all different troubles.
Zhenngguo Zhao