[BLAST_SHIFTS] summary 12/14

From: Tancredi Botto (tancredi@mitlns.mit.edu)
Date: Sat Dec 14 2002 - 23:42:46 EST


All day devoted to ABS. ABS dissociator was re-installed at around 2 pm.
Flow measuraments give ligit pressures as follows (sxpoles in)

status ligit (torr)

No abs flow 0.8e-9

injection valve open
Dissoc. RF off 5.5E-8

Dissoc RF ON 1.2E-7

RF_on-RF_off gives an idea of flow of atoms, after rejection of the
3,4 states *and* amplification from sx poles units. The above pressure
differentials were constant for a number of values of diss. RF power
and H2 flow, consistently with what was measured with a QMA 1 month
ago and in general with saturated dissociator operation.

Note, we have not optimized the nozzle position with respect to the
skimmer. We now have the capability to do so without opening vacuum.
The nozzle alignement was visually inspected, nevertherless.

We observed Delta-P = 6.7E-8 torr. If this was all atoms, it corresponds
to 1.5E16 At/s. However we know only a fraction is atoms.
If an 80 % fraction is atoms, the atomis flow is 1.2 E16 At/s

We proceeded to try measure dissoc fraction with the QMA (sxpoles off).
We have chopper signal but no chopped signal. We have no M=2
signal. We discard "dissociation fraction" masuraments for now.

We turned on the MFT units. With blast off, having the MFT on (at 60 MHz,
4.5 A current to the static field) reduces the differential flow by 40%.
In other words, the dissocation fraction -as measured from the MFT -
seems to be 80-85%. This is an upper limit as we assume that the MFT
efficiency is 100% Note, at the same time, with the qma signal alone,
we roughly estimate a diss. fraction of 2/3, with larger uncertainties.

With these caveats, then our estimate of a 1.2E16 At/s flow becomes
more realistic.

We will leave ABS on, MFT on for tonight and measure one full shift.
The holding field will be at 45 deg.

Abs work will continue tomorrow, when we will optimize intensity
at the nozzle/skimmer interaction. We realize that this is not an
optimization of actual flow inside the storage cell (rather of the flow to
the scatt chamber). The QMA needs to be looked at at somepoint.

-- VZ, TB, NM

________________________________________________________________________________
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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