[Hallc_running] [New Logentry] RC general updates for Hall C, Thursday swing to Friday swing

[mack at jlab.org]

Logentry Text:
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     No more issues with SHMS dipole PS trips. It seems the replacement of the timer module (used in a detect-heartbeat-or-shut-the-hell-down application) did the trick. 

    Moeller run was done on Fri day. (85.2+-0.4%) Thanks, guys! Opportunistic pNMR tests as well. 

    Took HMS/SHMS -3.5/-3.4 GeV data over Thursday nite with 3He target, longitudinal polarization. Good production. 

(There was  ~1hr of significant, multi-mm , slow, sinusoidal beam drifts. Dan Moser eventually traced it down to the locks having been put in a "suspend" state. He said he'd make an entry.) 

    Three target polarization measurements since restoration yesterday: 51%, 57%, and 53%. 

    Beam delivery Friday day problematic due to a serious trip in cryomodule 1L23, and then an injector issue. Longitudinal production resumed at 17:25 Friday. 

    Rapid progress was made Thursday nite in (mostly) resolving the target wall scraping issue that Bill Henry noted. Reducing the FR size from 4.5mm diameter to 4.0mm seemed to improve things, suggesting it was real scraping and not a FR artifact. https://logbooks.jlab.org/entry/3798113 Then JP shifted the beam position by 0.5mm in the correct direction(!) and it got even better, proving that scraping was involved. (confusing assortment of hclog entries on this) With 20/20 hindsight, it had been noticed that the burn scar on this cell window was offset, and the original carbon hole target plot indeed had a 1mm offset. https://logbooks.jlab.org/entry/3782272 So the apparatus is reproducible, but the sensitivity to beam position seems surprisingly high https://logbooks.jlab.org/entry/3798550 . Simona suggested checking the YAG viewer which showed no obvious nasty tail. https://logbooks.jlab.org/entry/3798716 Xiaochao et al will study the history.

The run plan is available at https://hallcweb.jlab.org/wiki/index.php/RC_Meeting_and_Run_Plan,_for_Friday,_March_6,_2020#General_updates: 

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This is a plain text email for clients that cannot display HTML.  The full logentry can be found online at https://logbooks.jlab.org/entry/3798786
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