[Sbs_gems] [EXTERNAL] Re: Test for GEp

Wed May 15 12:20:07 EDT 2024

Hi Bogdan

Yes, you are absolutely correct, it is a 30 cm target. I am sorry I missed that. So yes, it would be a factor of 6-7.

Yes, in that case it is good to push higher in the beam current for the test and also test the HV corrections on Sunday.

While I think that from the hardware perspective the GEMs would still be OK at that high luminosity,  I think Andrew might have a really  challenging problem with tracking with that factor of 6-7 increase: currently we are having raw occupancies of ~ 12.5 % , so given the same gain etc. we will have about 80-90% level occupancies for GEp; I do not think we ever expected or prepared for those level of occupancies (Andrew, please correct me if I am mistaken here); in my opinion, it would be next to impossible to run with anything higher than ~ 50-60% occupancy and get useful tracking information.

In that case we will seriously have to think about the hadron filter you have been proposing; and this Sunday could be an idea opportunity to test something like that.

Best

Nilanga

________________________________
From: Bogdan Wojtsekhowski <bogdanw at jlab.org>
Sent: Wednesday, May 15, 2024 12:07 PM
To: Liyanage, Nilanga K (nl8n) <nl8n at virginia.edu>; Sbs_gems at jlab.org <Sbs_gems at jlab.org>; Mark Jones <jones at jlab.org>
Subject: Re: Test for GEp

Hi Nilanga,

We can use BB tracker to monitor the beam stability and conformation from 50k analysis will good.
The difference between GEn-Rp and GEP operation is a bit larger:
GEP plans to use 50 uA on 30 cm long LH2 but GEn-RP used 15 uA on 15 cm LH2 => a factor of 6-7.
In addition, GEP will use SBS at 16 degree angle but now we have 23 degree.
So, it will be useful to see how GEM capable to operate with 30 uA on 15 cm long LH2.

Bogdan

________________________________
From: Liyanage, Nilanga K (nl8n) <nl8n at virginia.edu>
Sent: Wednesday, May 15, 2024 11:29 AM
To: Sbs_gems at jlab.org <Sbs_gems at jlab.org>; Bogdan Wojtsekhowski <bogdanw at jlab.org>; Mark Kevin Jones <jones at jlab.org>
Subject: [EXTERNAL] Re: Test for GEp

Dear All

Looks like thanks to all the hard work put in by Holly, Vimukthi and the team,  all GEM trackers are operating pretty well now, with efficiencies mostly around 75-80% per layer.

The current production running at 15 uA on LD2  is equivalent to about 25 uA on LH2; so about 50% of the GEp goal; this is consistent with the ~ 10-12% occupancies we are seeing in the SBS front tracker, I think Andrew was expecting about 25-30% for GEp.

Given this,  the high efficiencies, good tracking etc. we are seeing now are great signs for GEp.

As I mentioned earlier, what we are doing now  is much harder than the case for GEp: we are now requiring 3 hits out of 4 layers, while GEp will be asking for 4 hits out of 8 layers. This means that the layer efficiencies we are already getting are more than enough for GEp. Given the combinatorials of C(8,4) we should be able to get a very high tracking efficiency with what we already have. In fact, we might be able to lower the gains a bit to achieve more stable performance under higher luminosity, and still be able to get very good tracking efficiency in GEp.

We should be able to demonstrate this with the analyzer removed runs this Sunday

With the individual power supplies, is seems that the gains are pretty linear with beam current. So I think even at twice the current lumonosity we should be able to operate the power supplies like we are doing now, without any additional corrections to account for protective resistor voltage drops.

As for the program on Sunday, I do not think we need to push too high on the beam current, if we can get something like 25 uA on LH2 and LD2, that would be sufficient; with LD2 that would be close to 42 uA on LH2.

One thing we MUST remember for the beam test on Sunday is that the GEM gains are going to go up for both FRONT  AND BACK TRACKERS on SBS with beam current. This means that we may not be able to go to the same high voltage settings we are using for these chambers, especially for the back tracker ones,  for production right now. So, for the beam test,  we should back down all the GEMs voltages  to 3500 V and then carefully go up in voltage in 25 V steps while carefully monitoring the gains.

Also: if the beam is not stable and/or crappy, I think we should not turn on the GEMs on Sunday: given everything we have learned so far, there is nothing much left we must do to prepare for GEp. So if the beam quality is not good, I would rather not risk the GEMs to take some data which is not a must.

I plan to be there on Sunday

Best

Nilanga

________________________________
From: Sbs_gems <sbs_gems-bounces at jlab.org> on behalf of Mark Kevin Jones via Sbs_gems <sbs_gems at jlab.org>
Sent: Thursday, May 9, 2024 5:15 PM
To: Sbs_gems at jlab.org <Sbs_gems at jlab.org>; Bogdan Wojtsekhowski <bogdanw at jlab.org>
Subject: [Sbs_gems] Test for GEp

Hi all,
            Everyone has been working hard to get the GEMs working at this setting. Thanks to everyone.

For the next experiment GEp, we need to verify that the GEMs can be run at that
the luminosity of 50uA on 30cm LH2 target. Nilanga seemed fairly confident
that we can run at the GEp luminosity after the current scan that was early in the experiment.
       Do we need to do additional tests to show the expected performance for the GEp?
I am sure that we will get from Thia and Patrizia questions about the expected performance for GEp.

Cheers,
              Mark
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