[Sbs_gems] [EXTERNAL] Chance for GEM study at 20 uA?

[Andrew Puckett]

It’s now unclear whether we will attempt this today.

puckett.physics.uconn.edu

> On Nov 15, 2021, at 1:11 PM, Evaristo Cisbani <evaristo.cisbani at roma1.infn.it> wrote:
> 
> Dear Ezekiel,
> 
> 20% of current divider increase should be safe for the divider itself.
> 
> According to Dave Mack HV vs current analysis, and similar findings from
> Roberto, the first GEM foil becomes the most critical and at 20 uA of beam
> current it riches ~ 500 V. This is likely still safe: during assembly we
> tested all GEM sectors (in dry conditions) up to 550 V for few tens of minutes.
> 
> I am less confident about the foil distortion caused by the larger potential
> between foils (from about 750 V to 900 V); many years ago we did some Finite
> Element evaluations but I did not remember the conclusions and I have been
> unable to retrieve them from my documentation.
> 
> As suggested by Kondo and Nilanga, when you go at high beam current, please
> monitor the HV divider current; if it is not stable better switch of the
> chamber immediately.
> 
> Thanks
> 
> Evaristo
> 
>> On Mon, 15 Nov 2021 11:31:40 -0500
>> Ezekiel Wertz <ewertz at email.wm.edu> wrote:
>> 
>> Maybe that's more of a question for Evaristo. I do not know. I just want to
>> remind everyone that at 4100V (nominal setting for INFN GEM production) we
>> see about base current with no electron beam of 104 uAmp
>> 
>> Zeke
>> 
>>> On Mon, Nov 15, 2021 at 11:26 AM Ezekiel Wertz <ewertz at email.wm.edu> wrote:
>>> 
>>> Hi Nilanga,
>>> 
>>> The INFN GEMs will see probably about a 20-30 uAmp increase in HV at at 20
>>> uAmp of beam current. Is that safe for the divider since excess current
>>> would then be like 20% of the overall current load of the divider?
>>> 
>>> Zeke
>>> 
>>> On Mon, Nov 15, 2021 at 11:17 AM Liyanage, Nilanga K (nl8n) <
>>> nl8n at virginia.edu> wrote:
>>> 
>>>> Hi Sean
>>>> 
>>>> Thanks for letting us know.
>>>> 
>>>> Yes, it would be OK to get 20 uA on LH2. Please make sure to set the
>>>> current limits accordingly.
>>>> 
>>>> Later, for GEP-5 we will have to go to much higher currents, of the order
>>>> of 70 uA; so going to 20 uA now would be a good data point for us.
>>>> 
>>>> As Kondo has suggested before, while you are getting this current, please
>>>> monitor the GEM current, if it is not stable and keep going up (after the
>>>> initial increase following the beam current change), you my want to turn
>>>> the chambers off
>>>> 
>>>> Best
>>>> 
>>>> Nilanga
>>>> ------------------------------
>>>> *From:* Sbs_gems <sbs_gems-bounces at jlab.org> on behalf of Sean Jeffas <
>>>> sj9ry at virginia.edu>
>>>> *Sent:* Monday, November 15, 2021 11:01 AM
>>>> *To:* sbs_gems at jlab.org <sbs_gems at jlab.org>
>>>> *Subject:* [Sbs_gems] [EXTERNAL] Chance for GEM study at 20 uA?
>>>> 
>>>> Hi Kondo, Nilanga, and Evaristo,
>>>> 
>>>> The MCC is investigating some RF beam issues today, and they said that
>>>> they will send 20 uA of beam to hall A while doing their study. The
>>>> question is, can we keep the GEMs on to see the current draws at 20 uA? We
>>>> would try it on LH2, which has already been tested up to 10 uA. Here are
>>>> the numbers for currents at LH2 that we have taken so far:
>>>> 
>>>> No beam: https://logbooks.jlab.org/entry/3943588
>>>> 8 uA on LH2: https://logbooks.jlab.org/entry/3943079
>>>> 10 uA on LD2: Sadly no screenshots were taken, so I will quote the EPICS
>>>> values
>>>> UV Layer 0: 812 uA        INFN J0 bot: 116
>>>> UV Layer 2: 804 uA        INFN J0 mid: 118
>>>> UVa XY 0: 743 uA           INFN J0 top: 112
>>>> UVa XY 1: 768 uA           INFN J2 bot: 113
>>>> UVa XY 2: 769                INFN J2 mid: 113
>>>> UVa XY 3: 771                INFN J2 top: 0 (off)
>>>> 
>>>> 
>>>> So if we go up to 20 uA on LH2 I assume we double the excess currents
>>>> found here we would certainly pass the trip limits on all modules on the
>>>> front tracker. This For example UV layer 0 will go up to probably 870 uA.
>>>> Would this be safe? Are you guys ok with this test?
>>>> 
>>>> Best,
>>>> Sean
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>>>> 
>>> 
> 
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