[BTeam] bteam lead from 09/08 til 09/20

[Michael Tiefenback]

We have noted that the shift to 499 MHz laser frequency appeared to coincide with the Hall B tail reduction.  It was a dramatic effect.  Aiken mentions that this was done in coincidence with reducing the prebuncher amplitude.  Confounding factors abound.

I had considered the question of extinction ratio, wondering whether the alternate and not really intended pulses interleaved with the main 249.5 MHz train might have enough particle content to be the tails.  In this possibility, the even smaller bunch charge of the attenuated beam would change its low-energy propagation (both transversely and longitudinally) through the Wien region and chopper slit.  The "tails" in Hall B did not show signs of being longitudinally different from the body of the beam, but only differently transversely distributed.  Little to no dependence upon linac phase, for instance, which was a very early test.  After concluding that the transverse distribution might result from a head-tail "twist" of the beam, shortly thereafter frozen into its transverse distribution by the bunch compression, I would have moved toward testing pre-buncher sensitivity.  Fortunately, the issue became moot.  But we should seek to understand more than we now do.

Michael Tiefenback

________________________________
From: BTeam <bteam-bounces at jlab.org> on behalf of Matthew Poelker <poelker at jlab.org>
Sent: Tuesday, September 14, 2021 12:35
To: Michael Aiken <aiken at jlab.org>; bteam at jlab.org <bteam at jlab.org>; Shukui Zhang <shukui at jlab.org>
Subject: Re: [BTeam] bteam lead from 09/08 til 09/20

referencing Mike's comment on Hall B beam tails:

On topic of laser rep rate and beam quality, Yes, we can expect the laser pulse width to vary with rep rate, with shorter optical pulses obtained at higher repetition rates.  Perhaps with a shorter optical pulse, the hall B electron bunches became more similar to the other hall electron bunches, with more consistent results among the halls re: prebuncher setting.   Laser pulsewidth also varies with dc bias voltage and the amplitude of the rf applied, these parameters can be tweaked when troubleshooting beam at Hall B.

It was very smart to change the rep rate to see impact, clever.  Unfortunately, this is not always an option depending on beam energy received and what the other halls are doing. Glad it was an option this time.

Shukui has a draft paper on the green laser system he built for the GTS, so although the wrong color light for CEBAF, the behavior of gain switched diode lasers is the same.  Note, there is less timing jitter at higher rep rates too, another benefit of higher rep rate.

Encourage Shukui to finish this paper😉

Matt
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From: BTeam <bteam-bounces at jlab.org> on behalf of Michael Aiken <aiken at jlab.org>
Sent: Tuesday, September 14, 2021 12:22 PM
To: bteam at jlab.org <bteam at jlab.org>
Subject: Re: [BTeam] bteam lead from 09/08 til 09/20

I'm on shift and unable to host the meeting today.  I've compiled a list of relevant findings from the the previous week, as well things to think about for the near future:

[https://outlook-1.cdn.office.net/assets/mail/file-icon/png/docx_16x16.png]Bteam09142021.docx<https://jeffersonlab-my.sharepoint.com/:w:/g/personal/aiken_jlab_org/Eb9TtPHEoepPsNLU5wUjcE0BaLx6dMS6PPfmuq1kdd4_mw?e=Sds2Al>

It would still be useful to discuss some of these items among yourselves.  Freeman will be in training, but might be able to chime in towards the end.

-Mike Aiken
________________________________
From: BTeam <bteam-bounces at jlab.org> on behalf of Yves Roblin <roblin at jlab.org>
Sent: Wednesday, September 8, 2021 10:35 AM
To: bteam at jlab.org <bteam at jlab.org>
Subject: [BTeam] bteam lead from 09/08 til 09/20

I will be in vacation during this time.  Mike Aiken will be leading the Bteam. Todd Satogata will be available to perform CASA reviews as needed for ATLISes that requires it.


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