[BTeam] Fw: [EXTERNAL] Follow up on Hall B Halo Rates Troubleshooting

[Dennis Turner]

The hall folks did retract the collimator as a test, with no improvement to rates:

https://logbooks.jlab.org/entry/3835914

Dennis

________________________________
From: Brian Freeman <bfreeman at jlab.org>
Sent: Friday, August 28, 2020 6:01 AM
To: Michael Tiefenback <tiefen at jlab.org>; Dennis Turner <dturner at jlab.org>; HyeKyoung Park <hkpark at jlab.org>; bteam at jlab.org <bteam at jlab.org>; Stepan Stepanyan <stepanya at jlab.org>; Sebastian Kuhn <kuhn at jlab.org>; Paul Vasilauskis <vasilaus at jlab.org>; Mohammad Hattawy <mohammad.hattawy at gmail.com>
Subject: Re: [BTeam] Fw: [EXTERNAL] Follow up on Hall B Halo Rates Troubleshooting

All,

Re-including Hall folks here for comments.... as they stare at and understand their Halo counters/ Detector rates better than I.

One puzzling thing I noticed while digging is that the Upstream counters are quiet, the midstream only marginally increased on one counter (bottom), and the Downstream are noisy the right counter has almost double the counts as any others. If we had significant halo coming into the Hall wouldn't all counters have increased, or is this due to the focusing?

I don't think pre-buncher is worth touching as I could find no reason in the archiver to believe that it would do any good, and if it did we would likely have to put it back anyways, for the other Halls.

 So, additional items to add to the list are:

  1.
  2.  Injector check and retune has also come to mind .... alot a few hours for Yan/ Alicia to check the front end? We know the C beam has a tail from logs the other day, and we continue to have 0R08 BLM trips. ( 1 hr - 2hrs )
  3.  Re-steer at 2R->3S, this should be done regardless of the Hall B situation. After we re-steered at 2R after separation check I saw that Swing shift had difficulty with 7S01 BLM trips. The 3S01 vertical position isa at +7-8mm. I think we can improve this some. I also noticed that for some reason there is another BComm of design by 0.33%  ( MXS3R ), maybe fine but I would like to check this. ( 30 min to 1 hr ).
  4.  Given my above statements about no upstream counts. It could be possible that we should narrow our focus into the Hall from 2C24 to the target. Is it possible we are hitting the collimator that sits after the tagger magnet? Does the hall have insertables we don't know about? A valve, harp, or viewer simi-stuck in the beam line? We should simply cycle all insertables in the B line. (10 min)
  5.  We could simply try angle and position changes into the target ? It looks like things got really noisy after a target change in the hall on the 15th, probably a coincidence (https://logbooks.jlab.org/entry/3835820) . I believe that the Midstream counters sit around the Target somewhere, and Downstream counters are after CLAS. So perhaps we just have a bad angle going into the Target? ( 1hr )
  6.  Try focusing effects from the 2H00 and 2H00A quad pair that Tief/ Yves had mentioned in previous emails. Do we need to back up to the Tagger to do this?  ( 1-2 hrs ).
  7.  Open to other ideas from anyone.....


-Brian
________________________________
From: BTeam <bteam-bounces at jlab.org> on behalf of Michael Tiefenback <tiefen at jlab.org>
Sent: Thursday, August 27, 2020 9:15 PM
To: Dennis Turner <dturner at jlab.org>; HyeKyoung Park <hkpark at jlab.org>; bteam at jlab.org <bteam at jlab.org>
Subject: Re: [BTeam] Fw: [EXTERNAL] Follow up on Hall B Halo Rates Troubleshooting

We've had hints of scraping in 3S01 and vicinity.  It may be useful to test the sensitivity of 2R vertical (perhaps horizontal as well) steering.  The orbit locks steer the beam in the accelerator with some delay, not coordinating within the set of locks.  This flutter will move the beam by small amounts during the (very minor) steering tweaks.  If no effect on count rates is seen, then perhaps scraping is not the cause of the Hall B background rates.  Other diagnostic tests near the Hall B target are under consideration, too.

Michael Tiefenback

________________________________
From: BTeam <bteam-bounces at jlab.org> on behalf of Dennis Turner <dturner at jlab.org>
Sent: Thursday, August 27, 2020 21:03
To: HyeKyoung Park <hkpark at jlab.org>; bteam at jlab.org <bteam at jlab.org>
Subject: Re: [BTeam] Fw: [EXTERNAL] Follow up on Hall B Halo Rates Troubleshooting

Separation has already been rechecked.  First pass separation was tweaked, but no improvement for Hall B beam resulted:
https://logbooks.jlab.org/entry/3835771
https://logbooks.jlab.org/entry/3835775

Dennis

________________________________
From: BTeam <bteam-bounces at jlab.org> on behalf of HyeKyoung Park <hkpark at jlab.org>
Sent: Thursday, August 27, 2020 7:40 PM
To: bteam at jlab.org <bteam at jlab.org>
Subject: [BTeam] Fw: [EXTERNAL] Follow up on Hall B Halo Rates Troubleshooting

FYI
I presume BTeam has been pondering the results of tests and analysis.
Talk to you tomorrow,
HyeKyoung

________________________________
From: mhattawy at odu.edu <mohammad.hattawy at gmail.com>
Sent: Thursday, August 27, 2020 6:21 PM
To: Brian Freeman <bfreeman at jlab.org>; HyeKyoung Park <hkpark at jlab.org>; Stepan Stepanyan <stepanya at jlab.org>; Kuhn, Sebastian E. <skuhn at odu.edu>; Paul Vasilauskis <vasilaus at jlab.org>; Mike Spata <spata at jlab.org>
Subject: [EXTERNAL] Follow up on Hall B Halo Rates Troubleshooting

Dear HyeKyoung and all,
   Following up on the effort of understating the rates increase we see in Hall B and the logbook entry from Brian https://logbooks.jlab.org/entry/3835655. Brian reported on checking the laser phase on FC and the sensitivity to the 2C09 position. Unfortunately, we did not improve the situation and the rates are still increasing forcing me to reduce the beam current to 170 nA (from 180 nA).

Brian mentioned additional possible tests in his summary:
1. Check/ Recheck all Separation.
2. Check background relative to pre-buncher settings.
3. Test the sensitivity to Quad changes.

I would like to ask Brian if he can provide a time estimate for these additional tests and I would like to ask you if you can provide the manpower to continue this investigation tomorrow at the beginning of the day shift.

Best regards,
Mohammad Hattawy.
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