Hi,
Just a comment about the wire chamber tripping last night.
During the first part of the shift there was an attempt to run
without the BLAST magnetic field which was unsuccessful. The rates in the
BQM were not reported but this would be useful to know. In any case I
suspect the wire chambers charged up during this phase.
Then, when the toroid was turned on some boxes continued to trip.
Again, knowing what BQM rates were would be useful. I think the correct
thing to do in this case is to turn the WC HV off and have no beam for
about one hour and then try again. The shift turned off four boxes which
were tripping regularly and then continued to run.
Turning off the boxes and continuing data taking should be avoided
if at all possible. Each box usually connects to 5 cells. The inner
chamber has 18 or 19 cells so 5 corresponds to over 25% of the angular
range covered by the inner chambers. The middle and outer chamber have
26-27 and 34-35 cells so are a bit less important. With these cells
missing there is effectively no tracking through that region (there are
some fixes which can track with missing super-layers but it is a reduction
in efficiency if nothing else). So not only do we lose the data from these
tracking regions but if we wish to use these runs in any physics analysis
we have to run the Monte Carlo with these boxes turned off for the same
luminosity and spin states in order to compare the data.
The inconvenience of resetting the HV during a run has to be
weighed against shutting things down for an hour or the hassle of running
the MC with these same boxes off in order to use the data.
Of course ultimately boxes tripping is a wire chamber problem which
has to be solved. But for the past few weeks we have run the wire chambers
with relatively few trips and without needing to turn off boxes so I think
the BQM rates were probably high and/or the chambers had become charged
during the period with no toroid.
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
This archive was generated by hypermail 2.1.2 : Mon Feb 24 2014 - 14:07:29 EST