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

[Evaristo Cisbani]

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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> >>
> >