Hi,
Just to let everyone know what has been going on and what is being
done to solve the recent problems with the wire chambers:
1. On Monday evening Nick noticed we were out of iso-butane, he phoned
me, and I instructed him in changing the bottle.
2. The chambers ran fine for the rest of Monday evening and Tuesday
morning until we opened for the weekly shutdown.
3. Tuesday evening the wire chambers would not hold operating voltage.
Around 12 boxes had to be lowered by as much as 250 V. Tried re-tuning
the beam and turning the chambers off for several hours. Nothing
helped.
4. Wednesday afternoon Aaron and Tong changed the iso-butane again with
the suspicion that we had a bad bottle of gas. Aaron also added water
to the bubbler.
5. Thursday morning there were still around 6 boxes tripping or which
required voltages lower than required for efficient operation. I came
in to check things. Everything looked fine. The bubbler was not full
of water so I added about 2 litres. Since then I have been
conditioning the chambers with HV. Currently, without beam, they hold
4000 V (150 V above nominal). However, 4 boxes still tripped at noon
with beam so I have dumped the beam and continued conditioning the
wires. The chambers have been without beam in the ring for about 8
hours (except for one fill at noon). I will try operating the chambers
with beam again at 16:00.
In general it is not clear whether the problem is with the gas, water,
or something else. The problem developed after Nick changed the
iso-butane but also after the access Tuesday. Things improved after
exchanging the iso-butane again on Wednesday but not back to normal.
The chambers seem okay without beam but the inner chambers trip with
beam indicating it is beam related probably beam induced ionisation in
the chambers.
Plan for tonight is to try operating the chambers but with just 50 mA
of injected beam. If that works we will increase the current tomorrow
morning.
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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