[Sbs_gems] [EXTERNAL] Problems with J0 Mid

[Evaristo Cisbani]

Dear Ezekiel,

in case of short, the HV current at 4100 V, no beam should be around 114 uA
Therefore I expect there is a short in the middle GEM.

To be reasonable sure of the presence of a short, you can try to rump up the HV
at 500 and 1000 V; if the current is above the max current reported in the
manual (13.5 and 26 uA), then it is very likely a short.

In this case, one need to remove the protective resistor from the compromised
sector.

To do than one need to identify the sector; we used the thermo camera, which
requires to have a reasonable access to the GEM module. I do not know if this
can be done with the GEM in Bigbite.

Thanks
Evaristo
 
On Thu, 2 Dec 2021 22:12:21 -0500
Ezekiel Wertz <ewertz at email.wm.edu> wrote:

> Hi Kondo,
> 
> Thanks for the quick feedback. We will have to discuss the path forward,
> but it is good to know that the problem is identifiable.
> 
> Zeke
> 
> On Thu, Dec 2, 2021 at 10:10 PM Gnanvo, Kondo (kg6cq) <kg6cq at virginia.edu>
> wrote:
> 
> > Hi Zeke,
> > This crosses all the boxes of a shorted sector
> >
> > A gas window collapsed would not change the current.
> >
> > Best regards
> > Kondo
> > ------------------------------
> > *From:* Sbs_gems <sbs_gems-bounces at jlab.org> on behalf of Ezekiel Wertz <
> > ewertz at email.wm.edu>
> > *Sent:* Thursday, December 2, 2021 9:52 PM
> > *To:* Sbs_gems at jlab.org <sbs_gems at jlab.org>
> > *Subject:* [Sbs_gems] [EXTERNAL] Problems with J0 Mid
> >
> > Hi Folks,
> >
> > I was alerted by the shift crew to a problem with J0 Middle. At the moment
> > we are not entirely sure what has occurred, but the HV demonstrated some
> > problems and the efficiency of the module has become greatly reduced. See
> > the following log entries.
> >
> > https://logbooks.jlab.org/entry/3955216
> > https://logbooks.jlab.org/entry/3955221
> > https://logbooks.jlab.org/entry/3955220
> >
> > Also see the 50k replay plot for J0 mid on page 24
> >
> > https://logbooks.jlab.org/files/2021/12/3955238/summaryPlots_12496_bb_gem_for_shiftcrew.pdf
> >
> > Currently we suspect either a foil collapse or new shorted sectors in this
> > module. But we are uncertain of the actual cause which is why I am
> > contacting all of you. I have instructed shift crew to turn off J0 middle
> > HV until further notice
> >
> >
> > Ezekiel
> >