[Halld] [EXTERNAL] Re: update on the beam transmission activity

[Richard Jones]

Lubomir and all,

As you recall, I have been asking to develop a fast raster capability. This
would enable us to measure the 2D photon beam profile at the collimator as
a function of photon energy in real time, instead of "flying blind" in a
situation like this. Clearly the virtual spot we have right now is not a
simple product of 1D Gaussians, as assumed in the harp fitting tool. I am
not saying the harp fitting tool is useless, but it is based on sampling
the beam at a very few points far from the position of interest at the
collimator.

We have spent very little actual time developing the fast raster
capability, much less than has been wasted in the sort of re-tuning
attempts that have taken place over the past few days. Last time I sat down
to work with MCC expert Mick McCaughn on the fast raster, our work was cut
short by the Crew Chief who said it was not an approved activity. So unless
the collaboration comes together and decides to invest some time and get
the fast raster to work, and we communicate the importance of this
capability to the Accelerator Division, we are going to continue to stumble
forward in the dark like this and waste valuable beam time.

-Richard Jones

On Fri, Nov 12, 2021 at 6:54 PM Lubomir Pentchev <pentchev at jlab.org> wrote:

> *Message sent from a system outside of UConn.*
>
> Hello all,
>
> I just wanted to update you on the attempts to improve the beam
> convergence and transmission.
>
> Hovanes did his best to scan the active collimator to find the best
> position. He used both diamond and amorphous radiator, found somewhat
> better spot (off by fractions of a mm), but this didn't improve the
> transmission noticeably.
> The scan results also showed some asymmetries in the PS response when
> moving the collimator in x/y direction.
> After ~3h hours of studies at 16:30 we decided to go back to the original
> settings of the 5C11 quadrupole (as of yesterday before 13:00).  After that
> Hovanes performed another collimator scan, the distributions looked much
> more symmetric, and most importantly the transmission was restored to the
> yesterday's values. Even more, based on the last scan, Hovanes found new
> values for the beam position on the active collimator (0.0,-0.1) that
> improved the transmission by about 5-10%. We have not performed the harp
> scans to check the convergence, as the Ops were busy with setting up Hall
> A. This can be done later if needed.
>
> For more details look at https://logbooks.jlab.org/entry/3941683
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__nam10.safelinks.protection.outlook.com_-3Furl-3Dhttps-253A-252F-252Flogbooks.jlab.org-252Fentry-252F3941683-26data-3D04-257C01-257C-257C4f2fcbfb20f24970828d08d9a637ba9a-257C17f1a87e2a254eaab9df9d439034b080-257C0-257C0-257C637723580556981191-257CUnknown-257CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0-253D-257C1000-26sdata-3DkjMvp0vl9WdxzVVR0LAiqLYmHp1XHtwhiCaA1NT-252Fdv8-253D-26reserved-3D0&d=DwIFaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=iNGu2nyAzbYrgRkp14amkg&m=dgs4LWynqSiO_HSuULLehbr2Mr9caytZ2U4rKwYIgLg4FZAsXlS85WJiAUK2R92Q&s=a08Y_zTCjW4cB0783jvxDA-QuQZTVI8JGHDD5HlLmx8&e= >
> .
>
> We started production running at 17:30.
>
> Regards,
>  Lubomir
>
>
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