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

[Brooks, Stephen]

--[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>_______________________________________________
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>
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