[Sbs_gems] [EXTERNAL] Upper limits in terms of beam current for the GEM study planned for tomorrow

[David Armstrong]

Hi Folks,
    This will be a very interesting study!
  cheers,
    David

On 2/6/22 3:12 PM, Liyanage, Nilanga K (nl8n) wrote:
> Dear All
>
> My objectives for the high current study are to learn about challenges 
> in high occupancy running such as pileups in both time and space,  two 
> signals on the same strip separated by a short time) and two  hits on 
> nearby strips causing the clusters to merge. Even if we solve all 
> hardware problems like gain drop, we are sure to be limited by the 
> occupancy issues in GEp.
>
> Like Kondo said the highest beam current we can take will be limited 
> by the 1 mA limit on the GEM power supplies. The baseline GEM current 
> is about 735 uA, and we are running around 780 uA now  (with 5 uA of 
> beam current on LH2) ;  this is about 45 uA excess current in GEM. 
> Given this  we should be able to go five  times higher or more in beam 
> current before we hit this limit.
>
> So I would like to try to go up to 25 uA on LH2 and also on LD2, if we 
> can get those beam currents.
>
> We can do this in a few steps, say 5 uA steps in beam current. All we 
> need are short runs, say 10 min at each setting
>
> I agree with Alex that it is best to take these without zero suppression.
>
> As Kondo suggested, at each setting we can first take a run with only 
> one UV chamber turned on. After that run, if things look OK, turn the 
> rest of the GEMs and take another run, and then repeat this procedure 
> at the rest of the beam currents.
>
> If we only take  the high current runs with only one chamber on, and 
> not take the tracking runs with the other chambers on, then there is 
> nothing we can learn about pileup and this exercise would not be very 
> useful.
>
> So we must take tracking data to as high beam current as we can
>
> Best
>
> Nilanga
>
> Arun: Given accelerator limits and Hall C running, how much maximum 
> beam current can we take ?
>
>
>
> ------------------------------------------------------------------------
> *From:* Sbs_gems <sbs_gems-bounces at jlab.org> on behalf of Holly 
> Szumila-Vance <hszumila at jlab.org>
> *Sent:* Sunday, February 6, 2022 10:45 AM
> *To:* Rathnayake, Anuruddha (adr4zs) <adr4zs at virginia.edu>
> *Cc:* Sbs_gems at jlab.org <Sbs_gems at jlab.org>; Arun Tadepalli 
> <arunts at jlab.org>
> *Subject:* Re: [Sbs_gems] [EXTERNAL] Upper limits in terms of beam 
> current for the GEM study planned for tomorrow
> To be clear, the question is what current limits are we willing to 
> test up to for the gem test tomorrow on swing- probably a question for 
> Nilanga and/or Kondo. I think this is for coordination with MCC purposes.
>
>> On Feb 6, 2022, at 9:52 AM, Anuruddha Rathnayake 
>> <adr4zs at virginia.edu> wrote:
>>
>> 
>> Dear All,
>>
>> There is a discussion going on between our current RC (Arun) and some 
>> of us here in Jlab about what would be the beam current limits that 
>> we should adhere to, if it is possible to come into such a limit 
>> looking at the observations we have made so far.
>>
>> I'm attaching the GEM linearity studies we have done so far, if 
>> that helps to make a decision. https://logbooks.jlab.org/entry/3932489
>>
>> I believe if you use linearity studies done at SBS-11, that would be 
>> the best as our current spectrometer angles at SBS-9 are similar to 
>> what we had at SBS-9 (Please correct me if I am wrong, I know this 
>> more of as a word of mouth rather than referring to any official 
>> documentation).
>>
>> Best,
>> Anu
>>
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