[FFA_CEBAF_Collab] [EXTERNAL] Re: re JLab/BNL FOA response

[Berg, J Scott]

I like the idea of the iron plates. If we want to be neurotic, three plates so that each line sees symmetric iron. Probably doesn't even need to be that thick. Without the plates, we should look at a simulation, I would expect relatively significant fields outside, and spreading out enough that you're not going to get great shielding from the return yoke from the adjacent line. But the thing to do is check in a simulation, Nick probably even has 3-D maps from the CBETA correctors.

-Scott

> -----Original Message-----
> From: FFA_CEBAF_Collab <ffa_cebaf_collab-bounces at jlab.org> On Behalf Of
> Brooks, Stephen via FFA_CEBAF_Collab
> Sent: Monday, March 7, 2022 2:26 PM
> To: Jay Benesch <benesch at jlab.org>; Georg Heinz Hoffstaetter
> <georg.hoffstaetter at cornell.edu>
> Cc: ffa at cebaf <ffa_cebaf_collab at jlab.org>; Camille Ginsburg
> <ginsburg at jlab.org>
> Subject: Re: [FFA_CEBAF_Collab] [EXTERNAL] Re: re JLab/BNL FOA response
> 
> --[I think the 1200 MeV racetrack was your idea as it allows the
> electromagnets in the West Arc to be used as is.]--
> 
> It's an old idea and I only proposed it because the positron group at
> some point implied they wanted electrons up to ~1GeV to hit their
> production target.  Then I thought "OK, the least invasive way to do this
> is a self-contained e- and e+ injector at the first-linac-pass energy" so
> it's plug-and-play with the rest of CEBAF (apart from the positrons
> having to go anticlockwise and therefore the detectors being in the wrong
> place, requiring the transfer lines you added) and provides electrons for
> the e+ production target as well as CEBAF.
> 
> The 650MeV with a single electromagnetic recirculation loop is simpler,
> cheaper, smaller and has already been studied in some way as part of your
> ERL efforts.  It can also accelerate e+ but not simultaneously (the
> electromagnets in the recirculating loop would have to change polarity).
> Other option would be two recirculating loops on opposite sides if
> simultaneous e+ and e- is really needed, but that makes it wider, may be
> a problem for your hall.
> 
> --[I am pleased to learn that window-frame magnets big enough to fit over
> the permanent magnets can provide roughly the necessary steering fields.
> I trust they have a steel return outside the picture frame so the return
> fields from the first FFA's steerers don't affect the second centered 50
> cm below.]--
> 
> We didn't put this on CBETA (but we didn't have multiple FFA lines).  Not
> sure if it's necessary, maybe just put an iron plate between.  After all,
> the iron frame of the other line's corrector provides some shielding
> itself.
> 
>      -Stephen
> 
> ________________________________________
> From: Jay Benesch <benesch at jlab.org>
> Sent: 07 March 2022 14:11
> To: Brooks, Stephen; Georg Heinz Hoffstaetter
> Cc: ffa at cebaf; Camille Ginsburg
> Subject: Re: [FFA_CEBAF_Collab] [EXTERNAL] Re: re JLab/BNL FOA response
> 
> Stephen,
> 
> I think the 1200 MeV racetrack was your idea as it allows the
> electromagnets in the West Arc to be used as is.  I have no objection to
> altering it.
> 
> I sent the document out in the hope that the group could arrive at a
> consensus by noon Friday and get started on writing the FOA response on
> the basis of that consensus.  Although I'd like some weasel-words in the
> response in case we come up with a much better idea than the present
> baseline A+1 ;-)
> 
> I am pleased to learn that window-frame magnets big enough to fit over
> the permanent magnets can provide roughly the necessary steering fields.
>   I trust they have a steel return outside the picture frame so the
> return fields from the first FFA's steerers don't affect the second
> centered 50 cm below.
> 
> Jay
> 
> On 3/7/22 13:36, Brooks, Stephen wrote:
> > Also, in Jay's slides is there any reason why the rather complex 1.2GeV
> injector idea can't be replaced by the 650MeV single-loop injector
> throughout?  Is it because you wanted electrons and positrons
> simultaneously?  I don't see any disadvantage otherwise, unless you
> specifically wanted 1.2GeV.
> >
> >       -Stephen
> >
> > ________________________________________
> > From: Brooks, Stephen <sbrooks at bnl.gov>
> > Sent: 07 March 2022 13:33
> > To: Jay Benesch; Georg Heinz Hoffstaetter
> > Cc: ffa at cebaf; Camille Ginsburg
> > Subject: Re: [FFA_CEBAF_Collab] [EXTERNAL] Re:  re JLab/BNL FOA
> response
> >
> > Providing a dipole correction is in principle very easy with gradient
> magnets, since you can shift the magnet physically by a small distance.
> >
> > 18000 G.cm = 0.018 T.m = ~0.01 T Or less over the length of a typical
> CEBAF FFA magnet.  At 40T/m that's a 0.25mm shift.  I'm not 100% familiar
> but I think there are "piezo" movers that can be electrically operated to
> expand and contract over such small distances.  Although levers and gears
> and motors would be possible too...
> >
> > I'm reminded that CBETA's windowframe correctors that wrapped around
> the magnets could provide something like 0.02T or 1280G.cm, equivalent to
> a 2mm shift of the whole magnet (!)  So that's another possibility.  And
> those correctors were only 10-15cm long, same as the magnets.  For CEBAF
> FFA, our magnets are order of 2m long.  The permanent magnet is
> transparent to the field from the windowframe outside.
> >
> >       -Stephen
> >
> > ________________________________________
> > From: FFA_CEBAF_Collab <ffa_cebaf_collab-bounces at jlab.org> on behalf of
> Georg Heinz Hoffstaetter via FFA_CEBAF_Collab <ffa_cebaf_collab at jlab.org>
> > Sent: 07 March 2022 09:25
> > To: Jay Benesch
> > Cc: ffa at cebaf; Camille Ginsburg
> > Subject: [FFA_CEBAF_Collab] [EXTERNAL] Re:  re JLab/BNL FOA response
> >
> > Hi Jay,
> >
> > Is there space to put the correctors in-between the permanent magnets?
> >
> > Best,
> > Georg
> >
> >
> >> On Mar 7, 2022, at 8:54 AM, Jay Benesch via FFA_CEBAF_Collab
> <ffa_cebaf_collab at jlab.org> wrote:
> >>
> >> Colleagues,
> >>
> >> I created the attached to clear up in my own mind what the options
> are.  This may assist in writing the FOA response.
> >>
> >> The last two slides may throw a large wrench into the whole exercise.
> >>
> >> Jay
> <FFA_options_benesch_7mar2022.pdf>_______________________________________
> ________
> >> FFA_CEBAF_Collab mailing list
> >> FFA_CEBAF_Collab at jlab.org
> >> https://mailman.jlab.org/mailman/listinfo/ffa_cebaf_collab
> >
> >
> > _______________________________________________
> > FFA_CEBAF_Collab mailing list
> > FFA_CEBAF_Collab at jlab.org
> > https://mailman.jlab.org/mailman/listinfo/ffa_cebaf_collab
> 
> 
> 
> _______________________________________________
> FFA_CEBAF_Collab mailing list
> FFA_CEBAF_Collab at jlab.org
> https://mailman.jlab.org/mailman/listinfo/ffa_cebaf_collab