Operators: tancredi tancredi
This shift was devoted to ABS studies, collecting data on MFT and SFT scans
as described below.
At startup, HK tuned the ABS rf transitions. He reported problems with ligit
"bursts" and poor resolution in the compression tube ion gauge. Again, the
CT is the only tool against which you can tune/check the SFT,WFT transitions.
We investigated the issue of the CT ion gauge first: unfortunately instead of an
analogue read-out we have to digitize an analogue version of the digital gauge
controller read-out. Thus the gauge controller intrinsic ADC "resolution" may
affect the final radout value. We essentially toggled between two settings: HIGH
scale and a gauge calibration factor for D2, vs LOW scale and g.c.f. for N2 (this
is the default we have been using). In the first case the pressure reading is
multiplied by a factor 2.86 which we hoped could increase our sensitivity. The
manual is unclear about the HIGH and LOW scale but the HIGH seemed more
appopriate for pressures above 1e-7 (which occurs when the scale is set to D2)
We then turned to the MFT, as the MFT leaves a signal in both ligit and the CT.
The MFT can be tuned for 3-4 and 1-4 transitions. Each has different gradient
and static magnetic fields. Data was taken with WFT=SFT=off, gradient fields set
to -1.0 and -3.0 A (as recommented) and as a function of the static field in the 8.5
to 3.5 A range. Before the static field was scanned, the magnet hysterysis was
compensated for. The beam was off, blast and holding field were on and in "data
taking" conditions. Each scan was repeated 3 times.
The MFT static field is monitored by a gauss probe, and is cycled between -15
and 15 A. At those extremes the gauss probe reads -13 and 57 Gauss
respectively, which gives a clear indication of the direction of the BLAST field.
Therefore we decided to use the following recipe for taking out the hysterisys:
ramp the MFT to +15, -15, (+15, -15) and then go back to +15 and come down
monotonically from the high side.
Unfortunately this is done differently during data taking but I express my doubts
that you can cycle to the -15 point (low field) and then set the field for any given
transition. Also, since this was not critical for this measureement, we used a 2 s
setlling time instead of 0.4.
We then executed scans as described above, for both the MFT 3-4 and 1-4 (using
the different settings for the grad field) and for two sets of gauge settings.
At each value of the static field current we took 10 data points (1 second apart)
Results are attached in pdf, and shown as a function of time (left) and MFT current (right).
In these plots the time scale corresponds to 100 s = 7.5 A, 200 s = 6.5 A , 300 s = 5.5 A. The 3-4 and 1-4 resonances are clearly visible in ligit. The ligit burps are
also visible but they clearly do not pose a problem. Note that at each current
we do 10 measurements (which is the cause of the vertical bars on the right side
plots).
The CT tube signal is more problematic: it is not always there and I would
say in either scale for the gauge. We nevertherless chose "HIGH and d2 scale
factor" as our preferred setting since it seemed cleaner during the first MFT 3-4
scans. Also, the CT-bckg gauge (ideally not sensitive to the sx effects) seems
responsive to the incoming spin state, although this may only be an artefact.
Two main conclusion form these studies:
1) The CT is still not in a position to help (with reasonable confidence) the tuning
of the other ABS RF units. Therefore this tuning is ambiguous. The relative
efficiency of the WFT and SFT units is critical for the combined V-T analysis
we plan on D2.
I suggest changing cell since with this cell we have no CT signal.
2) Contrary to what was set by hauke for data taking, on july 05 the 1-4
transition does not occur at a static field current of 7.6. He pointed me to
some data from april 03. Please see for yourself: the cycle programs I used
are ~/pro2003/ABS/mft34.cycle and ~/pro2003/ABS/mft14.cycle. The data is
plotted with the respective .kumac files (in paw, just hit enter and then type
the name of the kumac. It is plain to see what input files are expected)
The difference regarding point 2) may have to do with hysterysis curve in the BLAST field. But I wish to hold to the considerations made in this email. It would
be interesting to compare with ion pol data for the 1-4/MFT-off.
We then turned to the SFT: to do so we leave the MFT in the (better known)
3-4 transition and we cylce the SFT static field. The SFT 2-6 and 3-5 transitions
are expect for the same value of the grad field. A plot is attached. In this plot
the scan is wider so 100 s = 9.5 A, 200s, 8.5 A and so on. The nominal transitions
for the SFT 2-6 and 3-5 are at a current of 4.6 and 9.9 respectively
During this scan ligit stays constant, as desired. Again burps are not an issue.
Again data was taken 3 times. The CT "sees" the small signal from a transition
although not reproducibly. Unfortunately we have a transition in both the
9.5-9.0 and in 4-3.5 range.
I do not know how to explain this: the 3-5 transition should not occur since state
3 is already taken out by the MFT. The consistency of this data also should be
checked against the ion pol data. For the SFT scan we used ~pro2003/ABS/CYCLES/sft26_mft34.cycle
The hysterysis procedure was the same as of the MFT, but it may have to be
different in case of SFT.
In summary: spent time developing a tool for routine checks of the ABS
transitions (thanks to VZ for giving me the blueprint and leave early). This
required more time than expected and taking over the target and preventing
data taking. On the other hand we wanted to wait long time for the Wch due to the fact the Wch had no He this morning.
Such a check of the ABS can now be done quickly. It does not take much more
then simply typing ABSsoft blabla.cycle. It is a few minutes per transition unit.
Data is presented in ascii to the out-file defined by the "log" command in .cycle.
We should plan on making this a standard routine. In particular these checks
may be useful at some point to compare the health of the transition units and
monitor "long term" stabilty effects.
Found that the MFT 1-4 does not occur where planned, the SFT tuning has no
clear signature. Therefore the target sequences for data taking seem junk. Discussed this with hauke at end of shift. However plan not to do anything until
these scans can be confirmed (or not) tomorrow. In particular, they should be
repeated tomorrow with the "previous" hysterysis cycle.
More worried about the CT, after all.
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