Mar 25, 2019
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Original Moller Polarimeter Page
Agenda:
- Commissioning report -- Sanghwa/Simona
- Simulation update -- Eric
- Simulation update -- Bill
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Meeting ID 388 466 836
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Minutes
Bill showed a compilation of data taken from commissioning runs. Systematic errors are a chief concern. No obvious reason seen in position variation.
Eric showed results of quad scans. Fall off at low quad values predicted in simulation still not apparent in data.
Questions posed by Don
- Were the scintillator paddles were turned off throughout the commissioning time? Ans. Yes. Scintillator paddles remained off.
- Was the raster on? Ans. No, raster was off.
Were intervening optics between upstream BPM's disabled? i.e. can we extrapolate the BPM's directly to obtain position on target?
- Can we insert an Al or C foil into the empty slot to measure a null asymmetry? Ans. Simona will check with Thia (budget/time) and Dave Meekins (time/availability) once the foil material and thickness have been determined.
- Should we make use of the insertable HWP to check systematics? Ans. This can be done quite easily once the beam is set up for parity running. Charge asymmetries should be at the 100 ppm level. We can use this as one test to differentiate between target and beam systematics.
- What is the plan to enable running at higher current (1 muA) on 10 micron foil? We don't want to have to take 2 to 3 times longer runs to get the statistics. Ans. Simona will follow up with Yves.
- We observed large systematic point to point errors during commissioning which made interpreting the data difficult.
a) Consecutive points taken at ostensibly the same settings have measured asymmetries of >2 percentage point differences, far outside the statistics. b) The 1 micron foil asymmetry was systematically lower than the 4 and 10 micron . Even the 1 micron at 3T was lower than the 4/10 at 2.5 T. Ans. It was observed during commissioning that calling for the target to move to a given position did not result in the same angle being read back, sometimes as much a 1 degree off from that specified. This needs to be further investigated as a contributing factor to the systematics.
- Is there any plausible explanation for the large systematic offset between 1micron and 4/10 micron foil asymmetry other than foil wrinkles? Should we ignore this for now and focus on solving the issues for 4 and 10 micron? --Undecided
- A quick estimate suggests that energy instability (dP/P) would not be sufficient to effect the precession into the hall by more than 1 deg or so. Anyone have better insight on this? Ans. Further look required.
- Is our best bet going to 4 T so that angle dependence and wrinkles have a small effect? Ans. Perhaps, but only if the systematic if target foil related.
- Is priority for next commissioning run to establish what level of repeatability we can obtain on 4 and 10 micron foils at 4 T? Check asymmetry systemtaics with non-magnetic foil, IHWP, and target holding field reversal? Ans. TBD
- Can we produce a stripchart of asymmetry vs time that is generated at end of each run? Ans. TBD
- Do we need more position information? What is BPM width? We have excursions at the 0.1mm level. Is this masked in noise? Will increasing slow sample rate help? Ans. TBD
