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I would opine that the dZ offset is negligible for us, but that the amount of offset the beam shows post-cryounit is much larger than 1.2 mm. The quoted 1.2 mm is _not_ the issue with which we struggle, and we have to buck the beam steering strongly (in my
recollection) between cryounit and the first viewer downstream. The _partially-corrected-by-steering-magnet_ offset is itself more than 1.2 mm. The hole size on the linac viewers is, as I recall, 3 mm (1.5 mm radius) and what we tolerate as partly corrected
is yet more than this.</div>
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Or so it seems to me. The blame has been placed on a transverse kick generated by RF fields in the cryounit, as I recall. I was not party to those determinations, and cannot guarantee more than that is what I think I remember. That is why I suggested to
Reza that we take this opportunity to move the cryounit transversely, presumably by the few-mm amount which was estimated in times past. Even partial correction would seem advisable.</div>
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For the consideration of this august assembly....<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> BTeam <bteam-bounces@jlab.org> on behalf of Todd Satogata <satogata@jlab.org><br>
<b>Sent:</b> Friday, October 2, 2020 08:01<br>
<b>To:</b> BTeam <bteam@jlab.org><br>
<b>Subject:</b> [BTeam] Injector Alignment</font>
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<div class="PlainText">(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>
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