[Rgc] RG-C Run Planning

[Sebastian Kuhn]

Dear all,

since I will be away for the next 2 weeks, I wanted to share with you where I think we are with the FTon part of RG-C and what I would suggest for those upcoming weeks. I will still be able to access email now and then, but I can’t guarantee that I can respond right away (much less join the RC meetings on a regular basis).

As you know, we agreed on 4 PAC weeks (= 8 calendar weeks) of FTon running before changing over to FTOut. Given that we had quite some struggle early on, both with beam delivery and with the polarized target, I estimate that we are about 2 calendar weeks behind at this point. I know that other halls are requesting extensions of their present experimental runs (Hall D unti 8/17, and Hall C probably even more than 2 weeks). Doug told me that his present update to the schedule has us penciled in for the changeover to begin with 2 weeks delay, on Thursday, August 25. Hopefully there will be an official announcement fairly soon.

At this point, we have collected data as shown below, together with the estimated remaining number of PAC SHIFTS (= x2 for real shifts) we would have to take on each target:

Fraction taken  PAC Shifts still Needed
NH3     46%     19.4
ND3     9%      32.5
C       44%     3.4
CH2     77%     0.4
CD2     0%      4.2
MT      100%    0.0
Sum     29%     59.9

Note that the total fraction of data we have already on tape is 29% of the expected for 4 PAC weeks, with a total of 60 more PAC shifts needed. The time elapsed so far corresponds to 59% of the initial 8 calendar weeks, but with the extension,we still would have 104 more shifts before the changeover. So we can MOSTLY if not fully catch up. Going forward, you can update these numbers (e.g., for the weekly Wednesday 1:30 MCC meeting) by dividing the total charge collected so far by the expected charge of 12 mC. (The MT target charge would have to be divided by 4 to account for the higher beam current). For the time elapsed, I use the days passed since 6/18/22 (first day of decent 10.55 GeV beam on target) until now, and divide by 56 (until further notice, i.e. when we get a new schedule).

As you can tell from the numbers above, we may still need about 2 calendar days (3 PAC shifts) of data on C, which could be scheduled whenever it is convenient (e.g.,, if we want to switch targets but don’t have time to go from one type of ammonia immediately to the other). Similarly, we need maybe 1 more shift on CH2 (put in in the morning, swap in the evening for C, e.g.). We have not taken any data on CD2 yet, but once this target becomes available (and if it looks like we’ll get some decent ND3 data), I would recommend planning at least 2 days of data taking on that. We do NOT need any more MT data.

I also want to reiterate that I strongly believe that it would be advantageous for minimizing systematic uncertainties if we would change the Solenoid polarity, e.g. next Thursday 7/28 during RF recovery. This would even out the difference in polarization degree for the two polarization signs, and I claim it would even help with systematic uncertainties from acceptance gaps etc., since it would basically result in an “independent” measurement of the same asymmetry, with different corrections. If y’all agree and do this next Thursday, I would probably try to postpone the C and CH2 remaining shifts until afterwards (see previous paragraph) to match the different running conditions, and split the CD2 between both polarities. However, that may not be too crucial.

Finally, here are some loose ends that hopefully can get taken care of over the next 2 weeks:
1) Complete the trigger file test series (maybe this evening?)
2) Execute the BMT HV test runs as requested by Yury and Francesco (once they come up with a specific test plan)
3) Assuming our irradiation and anneal is a success, switch the ND3 target polarization sign halfway between now and next Thursday. Also, keep flipping the HWP about once a day. Finally, take another Moller run (maybe right before or after the Thursday shutdown).
4) If possible, analyze the alignment run and apply alignment corrections as warranted.

Thanks, and may the beam (and target) be with you! - Sebastian

P.S.: One more request from (future) RCs: Please update the RGC RC wiki page daily:
https://clasweb.jlab.org/wiki/index.php/RGC_RC
by adding a headline with the date linked to that day’s RC Daily Update. You can add anything else below that (e.g. meeting time, discussion items,…), but even if you leave it blank otherwise, it will be a good way to quickly access all daily RC summaries. Thanks.

P.P.S.: I went to today’s Engineering meeting and presented our “wish list” for the changeover. Here is the compromise that we arrived at:

CHANGEOVER WORK TO BE DONE:
==============================

MUST:
———
1.) Disassemble beam line, remove downstream raster magnet, pull back target and solenoid, de-install FT and FTon Moller shield, install new ELMO Moller shield.
2.) Repair/replace any broken/flaky modules

SHOULD:
————
1.) Repair cold-tank NMR circuit; re-confirm target cell position
2.) Refill LTCC S2 (and S6 if we can get extra gas and sustain the high leak rate).

LIKE:
——
1.) Fix or replace x-Raster power supply with spare, check for oscillations (2nd magnet on floor)
2.) Search for and repair leaks in LTCC S2 and S6 - unfortunately not realistic.
3.) Fix remote control for shim coil currents


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