[BTeam] Hall A Energy discussion

[Brian Freeman]

Thanks for all the great discussion everyone!

I appreciate all of the responses and helps us all to understand what is being requested and why.

Adding to the list of Daniels links is when I was able to opportunistically measure what the max compression is:
https://logbooks.jlab.org/entry/3828665
I found that between 7 and 8 degrees is max compression, going further starts to de-bunch the beam, as apparent in Arc 1. Running the the NL off crest as well certainly will confuse things even more.

Can anyone explain why the compression knob is effective? Is it because the Compton is in a chicane and this magnetically compresses too? It would be interesting to perhaps have an SLM or even a viewer with in the chicane on the Compton beam lines to help?

I plan to have a closer look at global beam loss as a function of 0L04 phase, this is also maybe useful to determine what we are doing to the machine. Perhaps if it is just reduced size through the Compton it would be best to go back and try an Optics solution again?

Thanks again,
-B
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From: Daniel Moser <moser at jlab.org>
Sent: Monday, August 24, 2020 11:08 PM
To: Brian Freeman <bfreeman at jlab.org>; bteam at jlab.org <bteam at jlab.org>; Michael Aiken <aiken at jlab.org>; HyeKyoung Park <hkpark at jlab.org>; Paul Vasilauskis <vasilaus at jlab.org>; ciprian at jlab.org <ciprian at jlab.org>; Eric Forman <eforman at jlab.org>
Subject: Re: Hall A Energy discussion

1) The PID lock used to keep HALLA:dpp at -1.1e-4, its setpoint, only adjusts the gradient in 2L19-1, its output.
2) Yes, the Inj SLM spot with 0L04 +10.4deg off-crest is ~50% of the entire horizontal width. With the NL on-crest, the spot is not quite as long on the 1A SLM, but with it off-crest further negative, as it was taken at ~two points on Saturday for Hall A Compton background rates, the spot elongates further. Here are some screen grabs of what we see on the SLMs right now, NL crested,  https://logbooks.jlab.org/entry/3833462
3)  Back on 8/19, when trying to reduce xA Compton rates, I did first try to take the 0L04 gang phase closer to crest. Rates sky-rocketed. https://logbooks.jlab.org/entry/3831043 Interested to see what would happen if we tried again right now, given the optimized steering solution (see 5)).
4) 0L04 gang phase throughout run thusfar https://logbooks.jlab.org/entry/3832620
5) Eric Deir did excellent sleuth work Saturday evening, finding times when Compton rates were best, determining what orbit we had then, and then steering to it, bringing Compton rates down to ~5kHz. https://logbooks.jlab.org/entry/3832602

Of course I typed all this up hours ago, and now we are bringing Hall C online and finding 0R08 BLM trips are a big limiter to their current. Going to send this w/ the caveat of more to come. 0L04 gang phase has been reduced by 4degs, closer to crest.


________________________________
From: Brian Freeman <bfreeman at jlab.org>
Sent: Monday, August 24, 2020 8:21 AM
To: bteam at jlab.org <bteam at jlab.org>; Michael Aiken <aiken at jlab.org>; HyeKyoung Park <hkpark at jlab.org>; Paul Vasilauskis <vasilaus at jlab.org>; ciprian at jlab.org <ciprian at jlab.org>; Daniel Moser <moser at jlab.org>; Eric Forman <eforman at jlab.org>
Subject: RE: Hall A Energy discussion

Just some clarification  about the Hall A energy discussion of this morning.

  1.  Hall A is requesting a certain energy error (dp/p) -1E-4. This is an abnormal  request.
  2.  With FFB on in Energy mode,  or when running Arc 2 it does as designed and brings the error even closer to zero down to the E-5 range. So not sure what this request is about, and I believe this abnormal request is the root of the Hall A issue. (Cipran ?)
  3.  This issue with monitoring the SLMs, is that we are running 0L04 so far off crest that the spots almost encompass the entire image frame:
     *   https://logbooks.jlab.org/entry/3832990
     *   This was done to reduce Compton rates.
     *   I suggest we back out of the 0L04 change.

BTeam items for tomorrow's meeting? Yves you still on vacation?

Any others chime in, please.

-Brian
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