[FFA_CEBAF_Collab] [EXTERNAL] RE: FFA energy range

Thu May 25 15:09:22 EDT 2023

Dear All,

Interesting thread of thoughts… Perhaps, we should dedicate the next Friday mtg. to continue this discussion…?
As Todd mentioned, arcs with nonzero momentum compaction can be used to compress beam longitudinally. This is especially relevant for an RLA, where individual linac passes may have different gang phases. We considered such mode of operation for the LHeC ERL, where cumulative SR momentum spread was detrimental to energy recovery…
Certainly, higher order dispersion and momentum compaction effects on FFA Optics needs to be checked..

Cheers,

Alex
___________________________________
S. Alex Bogacz,
Accelerator Physics Group Leader
Center for Advanced Studies of Accelerators
Jefferson Lab
12000 Jefferson Avenue,<x-apple-data-detectors://8>
Newport News, VA 23606<x-apple-data-detectors://8>
___________________________________
Sent from my iPhone

On May 25, 2023, at 2:02 PM, Todd Satogata via FFA_CEBAF_Collab <ffa_cebaf_collab at jlab.org> wrote:

Heyos,

Longitudinal match is critical for high-power ERLs since they are
very loss-intolerant, a lesson David beat into me for ER at CEBAF and
JLEIC cooler work.

Running off-crest doesn't necessarily break this; indeed it is part
of the ER at CEBAF longitudinal match that Gus did with Alex and David
Williams. But it does have to be done in an integrated way, with
particular attention to higher-order compaction in the arcs (T566
and U5666). How big are those for the FFA arcs?

Alex should probably comment more with his experience. I'd worry
that it is a bigger effect than the SR-driven momentum spread when
pulling off crest enough to make appreciable (~10% or more) changes
in energy gain per module.

                                               -Todd

======================================================================
Todd Satogata
Director, Center for Advanced Studies of Accelerators
Jefferson Lab
12000 Jefferson Avenue
Newport News, VA 23606
Cell: (631) 807-0674
======================================================================

On 5/25/23 1:54 PM, Edith Nissen via FFA_CEBAF_Collab wrote:
That's a fair point about the longitudinal dynamics. My background is in synchrotron based boosters, so intuitively, to me, running off crest would be better than on crest. That being said, we would be switching between on and off crest rapidly without much in terms of synchrotron motion happening to smooth things out. It's probably worth simulating if tunability is something that's strongly desired by the users.
Edy Nissen
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
*From:* Brooks, Stephen <sbrooks at bnl.gov>
*Sent:* Thursday, May 25, 2023 1:28 PM
*To:* Kirsten Deitrick <kirstend at jlab.org>; FFA_CEBAF_Collab <ffa_cebaf_collab at jlab.org>; Berg, J Scott <jsberg at bnl.gov>; Edith Nissen <nissen at jlab.org>
*Subject:* Re: [FFA_CEBAF_Collab] [EXTERNAL] RE: FFA energy range
--[If we want some tunability in the energy, couldn't we keep the bottom energy of the FFA arc the same, then just do some path length adjustments to have the higher passes run off crest? that would be a knob to lower the energy not raise it]--
Yes, that would actually fix the problem!  I just don't know how much the longitudinal dynamics would cooperate with being off-crest.
      -Stephen
________________________________________
From: FFA_CEBAF_Collab <ffa_cebaf_collab-bounces at jlab.org> on behalf of Edith Nissen via FFA_CEBAF_Collab <ffa_cebaf_collab at jlab.org>
Sent: 25 May 2023 13:25
To: Kirsten Deitrick; FFA_CEBAF_Collab; Berg, J Scott
Subject: Re: [FFA_CEBAF_Collab] [EXTERNAL] RE:  FFA energy range
If we want some tunability in the energy, couldn't we keep the bottom energy of the FFA arc the same, then just do some path length adjustments to have the higher passes run off crest? that would be a knob to lower the energy not raise it (unless we leave some phase room in the nominal configuration).
It would make the splitters/recombiners a bit more complicated, and that may end up being a showstopper.
Edy Nissen
________________________________
From: FFA_CEBAF_Collab <ffa_cebaf_collab-bounces at jlab.org> on behalf of Berg, J Scott via FFA_CEBAF_Collab <ffa_cebaf_collab at jlab.org>
Sent: Thursday, May 25, 2023 12:15 PM
To: Kirsten Deitrick <kirstend at jlab.org>; FFA_CEBAF_Collab <ffa_cebaf_collab at jlab.org>
Subject: Re: [FFA_CEBAF_Collab] [EXTERNAL] RE: FFA energy range
If everything adjusted to keep the energy ratios the same in the splitters, then we would not need to do anything. If the ratios aren’t maintained, then there will be some steering adjustments needed. Presumably the same issue is faced in CEBAF.
-Scott
From: FFA_CEBAF_Collab <ffa_cebaf_collab-bounces at jlab.org> On Behalf Of Kirsten Deitrick via FFA_CEBAF_Collab
Sent: Thursday, May 25, 2023 12:05 PM
To: FFA_CEBAF_Collab <ffa_cebaf_collab at jlab.org>
Subject: Re: [FFA_CEBAF_Collab] [EXTERNAL] RE: FFA energy range
Isn't there a concern that just because the FFA can accept any energy in the range, the splitter lines won't have the necessary flexibility to provide position/angle for different energies? Or is this a case of "if we know we need it, we can make sure we have that flexibility"?
-Kirsten
________________________________
From: FFA_CEBAF_Collab <ffa_cebaf_collab-bounces at jlab.org<mailto:ffa_cebaf_collab-bounces at jlab.org>> on behalf of Berg, J Scott via FFA_CEBAF_Collab <ffa_cebaf_collab at jlab.org<mailto:ffa_cebaf_collab at jlab.org>>
Sent: Thursday, May 25, 2023 11:59 AM
To: FFA_CEBAF_Collab <ffa_cebaf_collab at jlab.org<mailto:ffa_cebaf_collab at jlab.org>>
Subject: [FFA_CEBAF_Collab] [EXTERNAL] RE: FFA energy range
Presumably this could also be addressed with a redesign of the FFA? I would think we could accommodate the additional energy range and flexibility at the cost of larger magnets and maybe some other modest penalties like radiation? Or is there something that stops this from working? I'm not suggesting it's the best choice, just an option.
-Scott
-----Original Message-----
From: FFA_CEBAF_Collab <ffa_cebaf_collab-bounces at jlab.org<mailto:ffa_cebaf_collab-bounces at jlab.org>> On Behalf Of Jay
Benesch via FFA_CEBAF_Collab
Sent: Thursday, May 25, 2023 11:53 AM
To: FFA_CEBAF_Collab <ffa_cebaf_collab at jlab.org<mailto:ffa_cebaf_collab at jlab.org>>
Subject: [FFA_CEBAF_Collab] FFA energy range

Colleagues,

I did not understand this limitation when we changed to one FFA.  I
suggest that being able to vary the beam energy is more important to
physics than 22 GeV.  It would make the splitters easier to design too;
for that matter it's not clear that six splitters fit in the tunnel at
all.

Jay

-------- Forwarded Message --------
Subject: Re: [EXTERNAL] Re: FFA energy range
Date: Thu, 25 May 2023 15:41:43 +0000
From: Brooks, Stephen <sbrooks at bnl.gov<mailto:sbrooks at bnl.gov>>
To: Jay Benesch <benesch at jlab.org<mailto:benesch at jlab.org>>
CC: Katheryne Price <kprice at jlab.org<mailto:kprice at jlab.org>>

Yes, essentially having the tunability costs you a turn because it
requires the FFA to accommodate lower energy beams at the low energy end
of the range, which would increase the ratio unless the highest energy
is also lowered.

You have three options:
~22GeV with no tunability, just discrete energies (14, 16, 18, 20, 22)
~22GeV with a percent or two of tunability, so a small range around each
energy above
~20GeV with close to full tunability (I haven't checked if it can 100%
cover with no gaps)

       -Stephen

________________________________________
From: Jay Benesch <benesch at jlab.org<mailto:benesch at jlab.org>>
Sent: 25 May 2023 11:36
To: Brooks, Stephen
Cc: Katheryne Price
Subject: Re: [EXTERNAL] Re: FFA energy range

Stephen,

I did not understand that.  If we had only five FFA passes, 20 GeV top,
could the good field region and tune accommodate some energy span?  The
users might prefer that to fixed energies, especially given the
unreliability of our SRF.

Jay

On 5/25/23 11:27, Brooks, Stephen wrote:
> There isn't any adjustable linac energy range in the 1-FFA solution.  This
is one of the requirements that ended up being dropped when we changed to a
single FFA.  Or to put it another way, accommodating linac tunability to get
a fully continuous energy range was one of the things that pushed me towards
the 2-FFA solution.
>
> Of course we could accommodate a couple of percent by running at slightly
dubious tunes.
>
>       -Stephen
>
> ________________________________________
> From: Jay Benesch <benesch at jlab.org<mailto:benesch at jlab.org>>
> Sent: 25 May 2023 11:22
> To: Brooks, Stephen
> Subject: FFA energy range
>
> Stephen,
>
> I've forgotten the allowed energy range as it's been a year since it's
> been discussed.  I remember linac energy range 1000-1100 MeV.  Is that
> correct?
>
> Jay

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