[BTeam] Injector Alignment

Fri Oct 2 12:39:02 EDT 2020

Thanks, Jay.

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.

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.

Michael

________________________________
From: Jay Benesch <benesch at jlab.org>
Sent: Friday, October 2, 2020 12:33
To: bteam at jlab.org <bteam at jlab.org>; Michael Tiefenback <tiefen at jlab.org>
Subject: Re: [BTeam] Injector Alignment

Mike,

I think it really is the FPC.  I can't find where I got the number, but
I recall a transverse kick that's a few percent of the accelerating
gradient.  Richard York's analysis of the emittance growth due to the
FPCs may have the number buried in it in a manner I can't discern.
https://jlabdoc.jlab.org/docushare/dsweb/Get/Document-33459/86-028.pdf

https://jlabdoc.jlab.org/docushare/dsweb/Get/Document-33629/89-132.pdf
does not seem to have the transverse kick.

Jay

On 10/2/20 12:10 PM, Michael Tiefenback wrote:
> 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.
>
> 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.
>
> For the consideration of this august assembly....
>
> Michael
>
> ------------------------------------------------------------------------
> *From:* BTeam <bteam-bounces at jlab.org> on behalf of Todd Satogata
> <satogata at jlab.org>
> *Sent:* Friday, October 2, 2020 08:01
> *To:* BTeam <bteam at jlab.org>
> *Subject:* [BTeam] Injector Alignment
> (Email forwarded from Reza bounce; originally to Joe Grames and
> Chris Curtis with CC: to Chris Gould, Matt Poelker, BTeam, Will
> Oren, Camille Ginsburg, Alicia Hofler, and Yan Wang at 07:15 Fri
> Oct 2 2020.)
>
> I had a good meeting yesterday (Thursday Oct 01-20) with Curtis,
> Gould, and Grames on Injector Alignment. The decision is to leave
> things as is.
>
> What does it mean?
>
> (Chris Curtis please correct me if I misstate something)
>
> According to the latest surveys (2008 & 2012) there is an offset of
> about 1.2 mm in X and 1.5 mm in Z between injector and North Linac
> coordinates. Everything before girder 0L03 is aligned to injector
> coordinates and everything from 0L03 and higher is aligned to NL
> coordinates.
>
> This situation causes almost no problem for us in operating or
> modeling of the Injector. Why? Because there is a long drift right
> before 0L03. A 1.2 mm X offset becomes unnoticeable in a long
> drift. (Z offset is even more insignificant)
>
> Now, if we attempt to eliminate this coordinates' difference during
> the Phase 1 of injector upgrade, this 1.2 mm offset will show up next
> year right at the choppers where the elements are much closer to each
> other and 1.2 mm offset will all of a sudden become significant.
>
> The other point to consider is that there is no guarantee that the
> North Linac won't move farther with respect to the injector in
> future. It may continue in the same direction or reverse course. Since
> moving all injector back and forth is not practical, my vote is to
> take this offset at a location which is least disruptive, and that
> would be 0L03 girder. In other words don't change anything.
>
> The only problem remains is what Chris Curtis brought up and that is
> potential for confusion when we align elements in the injector. We
> should keep clear documentation that 0L03 is the breakpoint and make
> sure there is no ambiguity in the sign of 1.2 mm.
>
> Chris, if you or other experts in alignment group start a tech note to
> document this, I would be happy to contribute to any part that falls
> under my expertise.
>
> I have added more recipients for the email. Please let us know if we
> are overlooking something important.
>
> Reza,
>
> Reza Kazimi
> kazimi at jlab.org
>
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