Status of TPC at PSI

[Claude Petitjean <claude.petitjean@psi.ch>]

Dear friends,

I like to give you a short account where we are in tuning up
our tpc:

2 weeks ago we had in the OLGA hall (East) the tpc nicely running
in 10 bar pure protium at up to 6.5 kV cathode voltage and with
an electrical drift field of up to 2kV/cm. We had on every wire
very nice signals from passing cosmic rays and/or the Sr90 beta
source.

But then a hot spot developed, clearly identifyable somewhere in
the middle of the tpc plane (anode B8 vs Cathode #17) which forced
us to pull the voltage back to 5 kV. Since we could'nt easily
recover, we took the protium out and filled in 10 bar Nitrogen.
At this (no-amplification) condition we could apparently burn up
the hot spot, and we are now nearing again 7 kV on the cathodes.

Our plan is to tune the tpc up next week in 5 bar N_2 and - if
successful - to move it into muE4 area. Meanwhile, Fred and Tom
have successfully cranked up the daq to a state where they want
to see real tpc signals.

Lets cross the fingers that this will happen soon!

With best regards

Claude