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Dear Jay:</div>
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Those are very good suggestions, and probably what we need at this moment for planning out the positron effort.</div>
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(And sorry for the price tag that comes with it.)<br>
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Xiaochao<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Jay Benesch <benesch@jlab.org><br>
<b>Sent:</b> Friday, July 2, 2021 9:11 PM<br>
<b>To:</b> Xiaochao Zheng <xiaochao@jlab.org>; pwg <pwg@jlab.org>; solid@jlab.org <solid@jlab.org><br>
<b>Subject:</b> Re: [Pwg] PAC Theory and Technical Review for Ae+e- Proposal (PR21-12-006)</font>
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<div class="PlainText">Colleagues, <br>
<br>
There are two accelerator working groups involved in the writing of white papers, one on positron sources and one on FFA permanent magnet replacement of the fifth pass electromagnets to increase energy to ~20 GeV. The former is concentrating on something that
requires the polarity of all the magnets in the machine to be reversed, requiring several weeks as mentioned in the TAC report. Since the FFA work assumes permanent magnets the scheme most recently considered, introduced by Andrei Seryi, allows only electrons
at energies beyond 8.8 GeV and could preclude them altogether, now that I think a bit more about it. For a few months I enticed the FFA working group into working on a much more expensive scheme, one which would allow electrons clockwise (as now) and positrons
counter-clockwise via a new 1.2 GeV ring, two new transfer lines and multiple positron injectors. We hadn't figured out how to get the positrons to halls A/B/C (or electrons for that matter at the higher energy, but a least no new tunnels would be required
for the latter.) This scheme would not require any magnets to change polarity since particle transport direction is reversed. Electron and positron transport from CEBAF to the Halls would differ. Monthly switches might be possible. Perhaps the response
to TAC point 2 could include something like "JLab's FFA working group has considered an expensive (~$1B) scheme which would provide simultaneous positron beams to three halls and allow changes from electrons to positrons in about a day. We urge JLab to more
fully explore this option in addition to less expensive ones that would provide electrons to ~20 GeV but positrons only to 8.8 GeV, after which permanent magnets would preclude field reversal. "
<br>
<br>
Jay <br>
<br>
________________________________________<br>
From: Pwg <pwg-bounces@jlab.org> on behalf of Xiaochao Zheng <xiaochao@jlab.org><br>
Sent: Friday, July 2, 2021 8:01 PM<br>
To: pwg; solid@jlab.org<br>
Subject: [Pwg] PAC Theory and Technical Review for Ae+e- Proposal (PR21-12-006)<br>
<br>
Dear All:<br>
<br>
We received the theory and technical reviews for the Ae+e- proposal today, please see attached.<br>
<br>
I will be drafting a point-by-point reply within the week and send it to the two PAC readers (Steven Dytman and Shufang Su) of our proposal. Please let me know by email if you would like to join the effort of drafting the reply.<br>
<br>
Cheers,<br>
<br>
Xiaochao<br>
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