[Clas12_rgh] beam energy

[Volker Burkert]

Eugene,

I thought we have given up on using the Hall C magnet.

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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