[Clas12_rgh] beam energy

Wed Aug 28 14:27:36 EDT 2024

On 8/28/2024 12:51 PM, Volker Burkert via Clas12_rgh wrote:
>
> Eugene,
>
> I thought we have given up on using the Hall C magnet.
>
Hi Volker,

I don't think we made a decision yet. What we decided is to resubmit the 
proposal to next PAC. I understood we have to converge by the end of the 
year with the configuration. Unless we will have a clear path for 
central detection we plan to go with the Hall-C magnet.

Since most of the expenses (beam line + target) are the same we can have 
a proposal with Hall-C magnet, which will make possible first running 
with transverse target, and later on submit upgrade proposal (basically 
just the new magnet+recoil) for additional time. Given the low 
luminosity running with transverse target we will certainly benefit from 
additional running with the new magnet.

Best,

Harut

> I am not saying we should run the program at 2.5 T. That was just an 
> example that I know from the past. We don’t want to give up the high 
> polarization at 5Tesla for the core RGH program. But at the 2-gamma 
> program that Axel mentioned one has higher rates and maybe the lower 
> polarization is tolerable.
>
> We should design the magnet for 5T. But if things go approximately 
> linear, I would think the target would also work at 11x4/5 and at 
> 11x3/5 GeV. Chris will know if he can get microwave generators at the 
> corresponding lower frequencies. So, to get to the lower energies we 
> could then just lower all magnetic fields of the chicane and of the 
> target magnet simultaneously and no mechanical changes might be needed.
>
> Volker
>
> *From: *Eugene Pasyuk <pasyuk at jlab.org>
> *Date: *Wednesday, August 28, 2024 at 12:37 PM
> *To: *Volker Burkert <burkert at jlab.org>, Axel Schmidt <schmidta at jlab.org>
> *Cc: *Eugene Pasyuk via Clas12_rgh <clas12_rgh at jlab.org>
> *Subject: *Re: [Clas12_rgh] beam energy
>
> Volker,
>
> If we go 2.5 T, the Hall C magnet or its clone would need some 
> modifications. To get the required field homogeneity at 5 T, it is 
> shimmed with an iron cylinder. It needs to be modified to go to a 
> different field, hopefully just a shim.
>
> But if we want to run at 2.5 T, we may just design a new magnet. The 
> forces on the coils will be smaller, and the coil supports could be 
> lighter. We may get larger acceptance.
>
> -Eugene
>
> ------------------------------------------------------------------------
>
> *From:*Volker Burkert <burkert at jlab.org>
> *Sent:* Wednesday, August 28, 2024 12:15
> *To:* Axel Schmidt <schmidta at jlab.org>; Eugene Pasyuk <pasyuk at jlab.org>
> *Cc:* Eugene Pasyuk via Clas12_rgh <clas12_rgh at jlab.org>
> *Subject:* Re: [Clas12_rgh] beam energy
>
> Hi Axel,
>
> For such a large range in energy it might be better to also lower the 
> polarizing target magnetic field with the chicane magnets and use 
> different microwave frequencies. The prize to pay is lower 
> polarization. In the past people have used 2.5 Tesla mag. field with 
> still decent polarizations (50-60% for protons??) . But Chris may want 
> to comment on this option.
>
> Volker
>
> *From: *Clas12_rgh <clas12_rgh-bounces at jlab.org> on behalf of Axel 
> Schmidt via Clas12_rgh <clas12_rgh at jlab.org>
> *Date: *Wednesday, August 28, 2024 at 11:52 AM
> *To: *Eugene Pasyuk <pasyuk at jlab.org>
> *Cc: *Eugene Pasyuk via Clas12_rgh <clas12_rgh at jlab.org>
> *Subject: *Re: [Clas12_rgh] beam energy
>
> Dear Eugene,
>
> Thank you for raising this issue.
>
> Acknowledging that the approved experiments are all designed for 5th 
> pass beam (and that obviously takes priority), I would be very curious 
> to know how much additional cost and effort would be needed to 
> accommodate 4th pass, or even 3rd pass beam energies. Lower energies 
> would probably be a lot better for measuring two-photon exchange, the 
> physics August and I are investigating.
>
> I realize that this would require a MUCH larger chicane bend. Would 
> this increase the size/cost/complexity by a large factor? At what 
> point does it become completely infeasible?
>
> We are still in the early stages for exploring this. We'll do 
> simulations and report to the group. But this seemed like a good 
> moment to register this point.
>
> Thanks,
>
> Axel
>
> On Aug 28, 2024, at 11:03, Eugene Pasyuk via Clas12_rgh 
> <clas12_rgh at jlab.org> wrote:
>
>     Hello RGH enthusiasts,
>
>     While thinking of the chicane design, it occurred to me that, so
>     far, in all our simulations, we have considered beam energy of 11
>     GeV. 11 GeV may not be available. Since the target magnet field is
>     fixed to be 5 T, we will have more bending for lower beam
>     energies. It has two consequences: more background in the forward
>     detector and a larger offset of the middle chicane magnets. The
>     latter means we would need a wider opening of the chicane magnets.
>     The maximum opening for the existing design that produces enough
>     BdL needs to be checked with the company. It may require a
>     substantial redesign of the magnet compared to the existing
>     version they built for someone.
>
>     We should define the minimum acceptable beam energy for this
>     experiment and run simulations with this condition.
>
>     -Eugene
>
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