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Thanks, Jay.</div>
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That agrees with my memory of the issue. I had thought at the time that rotating the downstream end of the cryounit by about 3 mm to the right would accomplish most of what we have (at various times) desired. But this is for others to consider. I recall
having suffered scraping issues at the 5 MeV (0L03 or thereabouts) dipole associated with this kick and offset.</div>
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I thought the issue merited careful deliberation. It's not my area of focus, but the injector is important to everyone. Sort of like a heart is of interest even to a podiatrist.<br>
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Michael<br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> Jay Benesch <benesch@jlab.org><br>
<b>Sent:</b> Friday, October 2, 2020 12:33<br>
<b>To:</b> bteam@jlab.org <bteam@jlab.org>; Michael Tiefenback <tiefen@jlab.org><br>
<b>Subject:</b> Re: [BTeam] Injector Alignment</font>
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<div class="PlainText">Mike,<br>
<br>
I think it really is the FPC. I can't find where I got the number, but <br>
I recall a transverse kick that's a few percent of the accelerating <br>
gradient. Richard York's analysis of the emittance growth due to the <br>
FPCs may have the number buried in it in a manner I can't discern.<br>
<a href="https://jlabdoc.jlab.org/docushare/dsweb/Get/Document-33459/86-028.pdf">https://jlabdoc.jlab.org/docushare/dsweb/Get/Document-33459/86-028.pdf</a><br>
<br>
<a href="https://jlabdoc.jlab.org/docushare/dsweb/Get/Document-33629/89-132.pdf">https://jlabdoc.jlab.org/docushare/dsweb/Get/Document-33629/89-132.pdf</a>
<br>
does not seem to have the transverse kick.<br>
<br>
Jay<br>
<br>
<br>
<br>
<br>
On 10/2/20 12:10 PM, Michael Tiefenback wrote:<br>
> I would opine that the dZ offset is negligible for us, but that the <br>
> amount of offset the beam shows post-cryounit is much larger than 1.2 <br>
> mm. The quoted 1.2 mm is _not_ the issue with which we struggle, and we <br>
> have to buck the beam steering strongly (in my recollection) between <br>
> cryounit and the first viewer downstream. The <br>
> _partially-corrected-by-steering-magnet_ offset is itself more than 1.2 <br>
> mm. The hole size on the linac viewers is, as I recall, 3 mm (1.5 mm <br>
> radius) and what we tolerate as partly corrected is yet more than this.<br>
> <br>
> Or so it seems to me. The blame has been placed on a transverse kick <br>
> generated by RF fields in the cryounit, as I recall. I was not party to <br>
> those determinations, and cannot guarantee more than that is what I <br>
> think I remember. That is why I suggested to Reza that we take this <br>
> opportunity to move the cryounit transversely, presumably by the few-mm <br>
> amount which was estimated in times past. Even partial correction would <br>
> seem advisable.<br>
> <br>
> For the consideration of this august assembly....<br>
> <br>
> Michael<br>
> <br>
> ------------------------------------------------------------------------<br>
> *From:* BTeam <bteam-bounces@jlab.org> on behalf of Todd Satogata <br>
> <satogata@jlab.org><br>
> *Sent:* Friday, October 2, 2020 08:01<br>
> *To:* BTeam <bteam@jlab.org><br>
> *Subject:* [BTeam] Injector Alignment<br>
> (Email forwarded from Reza bounce; originally to Joe Grames and<br>
> Chris Curtis with CC: to Chris Gould, Matt Poelker, BTeam, Will<br>
> Oren, Camille Ginsburg, Alicia Hofler, and Yan Wang at 07:15 Fri<br>
> Oct 2 2020.)<br>
> <br>
> I had a good meeting yesterday (Thursday Oct 01-20) with Curtis,<br>
> Gould, and Grames on Injector Alignment. The decision is to leave<br>
> things as is.<br>
> <br>
> What does it mean?<br>
> <br>
> (Chris Curtis please correct me if I misstate something)<br>
> <br>
> According to the latest surveys (2008 & 2012) there is an offset of<br>
> about 1.2 mm in X and 1.5 mm in Z between injector and North Linac<br>
> coordinates. Everything before girder 0L03 is aligned to injector<br>
> coordinates and everything from 0L03 and higher is aligned to NL<br>
> coordinates.<br>
> <br>
> This situation causes almost no problem for us in operating or<br>
> modeling of the Injector. Why? Because there is a long drift right<br>
> before 0L03. A 1.2 mm X offset becomes unnoticeable in a long<br>
> drift. (Z offset is even more insignificant)<br>
> <br>
> Now, if we attempt to eliminate this coordinates' difference during<br>
> the Phase 1 of injector upgrade, this 1.2 mm offset will show up next<br>
> year right at the choppers where the elements are much closer to each<br>
> other and 1.2 mm offset will all of a sudden become significant.<br>
> <br>
> The other point to consider is that there is no guarantee that the<br>
> North Linac won't move farther with respect to the injector in<br>
> future. It may continue in the same direction or reverse course. Since<br>
> moving all injector back and forth is not practical, my vote is to<br>
> take this offset at a location which is least disruptive, and that<br>
> would be 0L03 girder. In other words don't change anything.<br>
> <br>
> The only problem remains is what Chris Curtis brought up and that is<br>
> potential for confusion when we align elements in the injector. We<br>
> should keep clear documentation that 0L03 is the breakpoint and make<br>
> sure there is no ambiguity in the sign of 1.2 mm.<br>
> <br>
> Chris, if you or other experts in alignment group start a tech note to<br>
> document this, I would be happy to contribute to any part that falls<br>
> under my expertise.<br>
> <br>
> I have added more recipients for the email. Please let us know if we<br>
> are overlooking something important.<br>
> <br>
> Reza,<br>
> <br>
> Reza Kazimi<br>
> kazimi@jlab.org<br>
> <br>
> _______________________________________________<br>
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> BTeam@jlab.org<br>
> <a href="https://mailman.jlab.org/mailman/listinfo/bteam">https://mailman.jlab.org/mailman/listinfo/bteam</a><br>
> <br>
> _______________________________________________<br>
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> BTeam@jlab.org<br>
> <a href="https://mailman.jlab.org/mailman/listinfo/bteam">https://mailman.jlab.org/mailman/listinfo/bteam</a><br>
> <br>
<br>
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