[BLAST_SHIFTS] summary abs studies sunday

From: Tancredi Botto (tancredi@mitlns.mit.edu)
Date: Sun Dec 15 2002 - 14:20:05 EST


It becomes clear that we lose about 40-50 % of the ABS
flow by running at full current. We monitored dissociator
operation with a pion-diode mounted after a filter for the
first balmer line.

The pion diode show some response to different RF power at dissociator. We
monitored the dissociator operaation as a function of current in the blast
coils. The pin diode measuraments are consistent with a minimal change of
the power in the discharge, could be 20W at maximum. However the ABS
flow decreases. Note sextupoles are on, the atomic signal would be too
weak with out them.

We agree that there are 3 possibilities left, all other things being
constant:

_ The dissociation changes with the BLAST field. The pin diode
  measuraments are consistent with no change. But they would become
  hard proof only if they do see a change. However we really have no
  other way to check dissociation since the QMS is also not good.
  (note, the QMS is a long shot, 7-8 mt below the nozzle)

_ Since the sxpoles are in, we lose atomic focussing with blast field
  on.

_ LIGIT is fooling us and the flow is actually not changing.. But this has
  never been observed before, although ligit is affected by the target
  holding field. Ligit baseline pressure does not change. We are going to
  check it anyways

We confirmed our flow estimates of yesterday with blast data (normalized
elastic yield), lifetime and again with ligit. The atomic flow can
be at most 1.0-1.2 E16 At/s. This is a factor of 6 below maximum ABS
flow.
This is for 70 SCCM input gas, 300 W on the dissociator. By subtracting
a baseline pressure for when the dissoc RF is off we get the following
differential flows

        dissoc. delta-p

30 SCCM, 300 W 5.2E-8

70 SCCM, 300 W 6.4E-8

90 SCCM, 300 W 5.9E-8
90 SCCM, 400 W 6.4E-8

note, the delta-p signal is x10 times that of last week.
We decide to leave things at 70 SCCM, 300 W.

Tomorrow we should finally adjust the nozzle position, which is our
last handle on the intensity optimization. (note, today we were not
fully ready to do this).

-- VZ, TB

________________________________________________________________________________
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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