[FFA_CEBAF_Collab] [EXTERNAL] Re: Alternative FFA Arc - A tech note describing a brainstorm

[Berg, J Scott]

Ignoring the timing issue for now, this is essentially what Vasiliy and Randy have been working on, and just getting the match right turns out to be very challenging. The basic challenge lies in the "adiabatically" part: you're coming out of a linac with a beta function in the 10s of m, and need to get to an arc with a beta function around 1 m. For it to be truly adiabatic, you need something of the scale of 10% parameter change per cell. So the initial cells on the linac end will be very long and only slowly get shorter. Thus you end up with a very long transition line. Vasiliy and Randy have been working on making a shorter line, where the focus is more on matching individual energies, but we may be sacrificing energy tunability in doing so (apologies if I'm not getting the current state of that work quite right). 

As to getting the timing right, in principle we could design with nonlinear magnets and make the arc isochronous. But the beamline would suffer in terms of maximum field required in the magnets (or that would be traded off with larger magnets), and you're going to take a hit in radiation and emittance. I would argue that the hit you take in both of those is probably worse if you try to a more local orbit bump (the off-the-cuff argument for radiation is straightforward: you're always better off spreading your integrated field over a larger length).

-Scott

> -----Original Message-----
> From: FFA_CEBAF_Collab <ffa_cebaf_collab-bounces at jlab.org> On Behalf Of
> Brooks, Stephen via FFA_CEBAF_Collab
> Sent: Friday, December 8, 2023 10:02 AM
> To: Andrei Seryi <seryi at jlab.org>; Georg Heinz Hoffstaetter
> <georg.hoffstaetter at cornell.edu>
> Cc: ffa_cebaf_collab at jlab.org
> Subject: Re: [FFA_CEBAF_Collab] [EXTERNAL] Re: Alternative FFA Arc - A tech
> note describing a brainstorm
> 
> I think the devil is in the details.  Closed orbit bumps will probably not
> provide *enough* path length adjustment, when restricted to using practical
> fields and apertures.  They also have to be closed for all energies
> simultaneously, which becomes more complex as the number of passes
> increases.
> 
> Also, having independent adjustment of the passes is probably good
> operationally.
> 
>      -Stephen
> 
> ________________________________________
> From: FFA_CEBAF_Collab <ffa_cebaf_collab-bounces at jlab.org> on behalf of
> Georg Heinz Hoffstaetter de Torquat via FFA_CEBAF_Collab
> <ffa_cebaf_collab at jlab.org>
> Sent: 08 December 2023 08:59
> To: Andrei Seryi
> Cc: ffa_cebaf_collab at jlab.org
> Subject: [FFA_CEBAF_Collab] [EXTERNAL] Re:  Alternative FFA Arc - A tech
> note describing        a       brainstorm
> 
> Hi Andrei,
> 
> This is an excellent strategy and the ultimate application of FFAs for
> recirculating system. I would love to see this realized some day. Dejan and
> I, and others, have talked about this a lot and it has been considered.
> Alas, there are space constraints. Dejan, Scott, and Stephen, can probably
> tell more about the specific problems.
> 
> All the best,
> Georg
> 
> 
> 
> 
> 
> On Dec 8, 2023, at 8:41 AM, Andrei Seryi via FFA_CEBAF_Collab
> <ffa_cebaf_collab at jlab.org<mailto:ffa_cebaf_collab at jlab.org>> wrote:
> 
> Colleagues,
> 
> I was talking to Thomas Roser last week at DESY about our design.
> He suggested to avoid spreaders and combiners altogether, and instead use
> FFA-like beamline that adiabatically transition to regular FFA of the arcs.
> I.e., it will be FFA with varying cell length – starting from longer near
> linacs, to shorter cell in the arcs.
> The timing corrections of individual energies can be done by some closed
> bumps.
> Can this be considered?
> 
> Thanks
>    Andrei
> 
> 
> 
> From: FFA_CEBAF_Collab <ffa_cebaf_collab-
> bounces at jlab.org<mailto:ffa_cebaf_collab-bounces at jlab.org>> On Behalf Of
> Ryan Bodenstein via FFA_CEBAF_Collab
> Sent: Thursday, December 7, 2023 11:35 AM
> To: ffa_cebaf_collab at jlab.org<mailto:ffa_cebaf_collab at jlab.org>
> Subject: [FFA_CEBAF_Collab] Alternative FFA Arc - A tech note describing a
> brainstorm
> 
> Dear FFA Colleagues,
> 
> Since we’ve been entertaining a lot of alternative options lately, I
> thought I’d add to the pile.
> 
> I’ve spoken to a few of you about this, but I thought I’d write it down
> informally and share it with the group. Please note: this is no more than
> brainstorming put to paper (or digital paper, if you will). But it
> describes a few alternative ways to design the FFA arcs. These ideas may or
> may not be feasible, and may or may not help things. They will likely cost
> more, but may be worth it.
> 
> Attached, you’ll find a copy of the tech note. If you are on JLab’s
> network, you can also find it here:
> https://jlabdoc.jlab.org/docushare/dsweb/View/Collection-55373
> 
> Cheers!
> Ryan
> 
> Dr. Ryan Bodenstein (he/him)
> Staff Scientist II – Center for Advanced Study of Accelerators (CASA)
> <image002.jpg>
> 12000 Jefferson Avenue
> Newport News, VA 23606
> United States of America
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