Dear Colleagues,
People who will run shifts must read this.
For the past day or so we have been unable to take data because of a
problem with the right sector wire chamber. The situation developed
after the maintenance day Tuesday when the gas bottle for helium and
iso-butane were changed. It also happened after changes were made to
to the beam tune. It is not clear what caused the problem. The
symptom is that the TDC distributions for the right sector are not flat
as normal but slope down from the peak corresponding to the sense wire.
This implies that the electrons which are produced by tracks far from
the sense wire do not reach the sense wire. This can be explained in
terms of some gas contamination, a leak, or possibly insufficient flow
of gas through the right WC.
On Wednesday, when the problem was noticed by Ben, we first increased
the flow from 4 to 5 l/min. After 3 hours this had no noticeable
effect. Around 15:00 we replaced both helium and iso-butane bottles to
see if the problem could be due to a bad batch of gas. There was no
quick improvement but we decided to let the gas flow overnight to give
it a chance to flush thoroughly.
Thursday morning the problem was still there though it was slightly
better. We then opened the hall and Chris Vidal and Jim Kelsey
modified the gas system to disconnect the left sector so all gas was
flowing through the right sector. The situation improved after a few
hours. Chris and Jim re-routed some flexible pipes and looked for
other potential problems. In the afternoon they put the gas system
back together and we have started running again.
The right sector TDC distributions are not perfect yet but are quite
good. I think we can use this data for analysis again.
***** NOTE *****
However, the shift crew should be very careful to watch the right
sector TDC distribution for each run. If it does not continue to
improve or if it starts to get bad again I should be notified
immediately.
***** NOTE *****
If the problem re-appears we can switch to helium-3 in the unpolarised
system tomorrow and study intensities over the weekend. The WC's even
in a weakened start are working well enough for this work.
On the longer term Jim and Chris are investigating getting the extra
plumbing and fittings required to bring the return gas lines from each
sector back to the gas control panel and connected them to separate
bubblers with some way to regulate the flow. This would likely take
two days to install once all the parts are available.
Cheers,
Douglas
26-415 M.I.T.
Tel: +1 (617) 258-7199
77 Massachusetts Avenue Fax: +1 (617)
258-5440
Cambridge, MA 02139, USA E-mail:
hasell@mit.edu
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