Hi Flemming & Dana;
We are writing to you concerning your recent Memorandum
which contains some asumption about a gas supply system.
Here in Krakow, dr. C. Garabatos (CERN/GSI) gave a seminar
on Ageing of Drift Chambers and our comments are influenced
by discussion with him.
1. Ethane gas in not good choise with respect of the ageing problem.
His other suggestion is to use isobutane gas (more expensive, but
we have to run a long time).
2. Gas flow is also underestimated in the Memorandum. In the MIT chambers
a gas has been replaced in 20 minutes. The paper presented at 1987
Nucleare Science Symposium (San Francisco Oct. 19-20) R. Herdenson
et al., indicates that: exchange of the entire volume of the detector at
about 2 times/minute causes that the aging is 2 or 3 times less effective
than with 10 times slower flow ( 0.2 volume/minute ). Such fast flow
in practise can't be applied but this statements show the evident relation
between the flow rate and the aging properities of the setup.
3. Another problem is connected with gas supply tubes.
Here, plastic, rubber has to be eliminated everywhere
where it is possible.
More precise estimation we will send to you in early January.
Best regards;
Zbig & Tom
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