Doug, I took the field off data last night. BQMs were OK: 190/200/80/110
with a more aggressive slit position (lifetime from 30 to 13 min, 0.05
SCCM gas). It looked ok enough that we went to ion pol studies. One trick
was to limit the injection current to 70 mA. Although the above
conditions were fine for 0.5 hr (at about 9 pm) when we started data
taking the chambers tripped to often. We should try again.. I am not sure
if only a few of the wires were to blame (again, went to ion pol studies)
-- tancredi
P.S. I spoke w/ adrian and peter: after ca. 3 hrs of quite operation with
field on (the field off was aborted) a few wires (one box?) started to
repeatedly trip. They noticed it was only a few so they asked for
instruction on how to switch those off so as to keep taking data for the
night. I do not know about bqms at that time but you can easily check that
in scalers. True, by morning they had to let the wch rest for a while
which suggests the recipe you prefer may indeed be the best:
1) check bqm history
2) wait 1 hr with wch off, no beam first
3) call wch expert to change/switch-off hv ??
________________________________________________________________________________
Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124
research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
On Thu, 29 May 2003, Douglas Hasell wrote:
> 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
>
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