====
Tried optimizing beam backgrounds as a function of beam position (local
bump) at the septum, after storage. I based myself on singles (PHYS2 and
PHYS3). There seems to be some improvement if you move slighty away
from the septum (1 mm) but the you lose again. Needs confirmation
see pg 58,59
also, optimized slits with a gas flow of 0.2 SCCM. *note* we
should compare results at equal currents since non-linear effects will
be important inthis fine tuning. The single-arm background is 10 %
different at high (100 mA) relative to medium currents (80 mA). It seems
flatter after that (see also past logbook plots)
Typically a lifetime of 8-10 minutes at high currents gives a smooth
running. So don't be shy we the slits ! Also, if the difference between
two facing slits is > 15 (nominal mm) you are probably not cutting enough
with one of them. We should try to find the edge on both sides.
=======
Measured magnetic field at CC. Vertical field is up to 200 gauss in
the central region and up to 100 gauss pointing away(in) from the PMT
can. TDR assumed 150 gauss max vertical, 50 gauss horizonthal.
However, on LC0 and RC0 the field is max 50 gauss, while we seem to
already have a problem there. Needs analysis results.
Also, TDR gives an average of ca 3 PE when a "central reflector" is
not used (is it used then ?). With 3 PE, the efficiency is 95 %,
but drops to 80 % is we trigger above the 1 PE peak.
========
Chris De Andrea debugged, took data and analysed cosmic NC data. VZ and
TS are investigating "last" remaining issue (had to do with an apparent
TDC inefficiency)
________________________________________________________________________________
Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124
research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949
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