[Mott] Mott work summary Feb. 13th

[Joseph Grames]

Mott work summary for Thursday Feb. 13th is shown below. For those off-site you can access electronic logbook (https://logbooks.jlab.org) with your JLAB username and password to view all entries, pictures, plots, etc.

Last night we completed ~final adjustments for timing and pretty much "fixed" the DAQ and documented to the wiki.  Then, moved to 31MHz and set polarization vertical P=P0<y> and measured asymmetry and reversal with optical lambda/2 waveplate.  Using our standard 40.04% effective AP for 1um Au found polarization of about 87%, very rewarding start.  We then measured (physics asymmetry, instrumental asymmetry, rate, deadtime) as a function of a) beam current 0-5uA, b) 9 positions on target, c) dump dipole, d) empty target frame, e) spot shape (best, normal, degraded).  We found we could indeed vary the instrumental instrumental asymmetry from zero to large ~20% values and the fraction of relative "good" elastic to "bad" background rates, but in each of those ~25 measurements (calculated using TOF cut, elastic cut and super-ratio method 2 detectors, 2 helicities) found a physics asymmetry consistent with one another to the point-wise ~0.6% statistical uncertainty.  Broadly, it was easy to generate a typical beam to Mott with consistently zero instrumental asymmetry at good operating rate ~2kHz (dead<6%) and clean 31MHz elastic separation, good elastic:background contributions.

We will take Friday and possibly Saturday OFF, definitely to return on Sunday to complete final pass of systematic studies and then move into a program of collecting asymmetry on foils.  I'll forward around our proposed plan in the meanwhile.

-Joe

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1600 - Shift starting

1715 - Have been done for 1 hour. Problem was a HV cable not plugged into back of ISB PS.

1745 - Beam setup to Mott at KE=5.0MeV and checked setup script again.

1800 - Many faults on BLM HV, need to mask many bits to get stable configuration.

1805 - Running 0.5uA on 1um Au target to check against shutdown 2 nights ago.

1850 - Measured dE/E timing at ISB, adjusted dE timing to middle of E; took pics and 7301

1855 - Switched to 31MHz on C laser; beam spot coincident w/ A; looks good, moving on.

1905 - Adjusting BFM delay to account for dE/E timing shift of 12ns

1949 - Changed HWien=+89, sending measurable polarization first time

2013 - Measured beam polarization with IHWP OUT/IN. OUT=>87.4%, IN=>-87.2%

2100 - Completed rate/asymmetry/deadtime vs. intensity 0.5-5.0 uA @ 31MHz on 1um Au

2115 - Spent a little time to improve transmission at A2/MS; had forgotten x16 factor in bunch charge! :) For tonight will run at ~1uA to Mott for systematic studies.

2240 - Completed asymmetry vs. position on 1um Au

2310 - Completed asymmetry vs. dump dipole and thru hole

2350 - Completed asymmetry vs. spot size/shape

2355 - Backing out quad and HWien changes.