[Sbs_gems] [EXTERNAL] UV GEM HV Settings

[Sean Jeffas]

I suppose we need a clearer description for signs that the detector need a
higher voltage setting. As Andrew has been working with the analysis
software he has repeatedly maintained that the we should not go off of the
GEM efficiencies that the analysis quotes. So what should we look for to
decide that the voltage is getting too low?

>From my knowledge all that we have is the HV efficiency scan. Even if the
tracking is not perfect, it will still show us the correct shape, with the
plateau efficiency values. We set the voltages originally using the values
found during commissioning here https://logbooks.jlab.org/entry/3925085. If
we look at UV layer 0 (uva_uv_l0_m0) and UV layer 2 (uva_uv_l2_m4) we see
that going from 3697 V to 3653 V drops us by about 5% efficiency, which is
fine. But during this last week, with 5 uA on LD2 we usually found UV layer
0 and UV layer 2 running around 70% efficiency. So what should we actually
look for to decide that something needs to change?

Best,
Sean

On Thu, Nov 18, 2021 at 3:50 PM Gnanvo, Kondo (kg6cq) <kg6cq at virginia.edu>
wrote:

> Sean, all
>
> There is no reason to change from previous setting. Like Nilanga said, we
> should stick to the setting we had before.
>
>
>
> The new chamber need HV scan to know the optimal value (don’t assume that
> it is the same exactly than the other UV layers). You can start with 3653
> and see what you get or do a HV scan. But keep I mind that we need to be
> careful regarding increasing the HV before we really understand all the
> consequences in modifying HV divider.
>
> If there is no clear reason, to go higher I would be very conservative.
> That is my default mode
>
>
>
> Best regards
>
> Kondo
>
>
>
> *From:* Sbs_gems <sbs_gems-bounces at jlab.org> *On Behalf Of *Holly
> Szumila-Vance
> *Sent:* Thursday, November 18, 2021 3:45 PM
> *To:* Andrew Puckett <puckett at jlab.org>; Liyanage, Nilanga K (nl8n) <
> nl8n at virginia.edu>; Jeffas, Sean (sj9ry) <sj9ry at virginia.edu>;
> sbs_gems at jlab.org
> *Subject:* Re: [Sbs_gems] [EXTERNAL] UV GEM HV Settings
>
>
>
> 3653 for layers 0,2 and new 3. The back tracker has had no changes.
>
>
>
> *From: *Sbs_gems <sbs_gems-bounces at jlab.org> on behalf of Andrew Puckett <
> puckett at jlab.org>
> *Date: *Thursday, November 18, 2021 at 3:43 PM
> *To: *"Liyanage, Nilanga K (nl8n)" <nl8n at virginia.edu>, "Jeffas, Sean
> (sj9ry)" <sj9ry at virginia.edu>, "sbs_gems at jlab.org" <sbs_gems at jlab.org>
> *Subject: *Re: [Sbs_gems] [EXTERNAL] UV GEM HV Settings
>
>
>
> Okay, so then what are the recommended settings for ALL UVA
> layers/modules? I’m confused. Because we have been running with a mix of
> 3653 and 3697
>
>
>
> Andrew
>
>
>
> *From: *Sbs_gems <sbs_gems-bounces at jlab.org> on behalf of Liyanage,
> Nilanga K (nl8n) <nl8n at virginia.edu>
> *Date: *Thursday, November 18, 2021 at 3:30 PM
> *To: *Jeffas, Sean (sj9ry) <sj9ry at virginia.edu>, sbs_gems at jlab.org <
> sbs_gems at jlab.org>
> *Subject: *Re: [Sbs_gems] [EXTERNAL] UV GEM HV Settings
>
> HI Sean,
>
>
>
> No, I think it would be best to run at 3653 V  with this modified divider
> for right now.
>
>
>
> We are going to study the modified divider with the  x_ray source here
> over the new couple of weeks. Once we know more, we can consider going
> higher if needed
>
>
>
> Best
>
>
>
> Nilanga
> ------------------------------
>
> *From:* Sbs_gems <sbs_gems-bounces at jlab.org> on behalf of Sean Jeffas <
> sj9ry at virginia.edu>
> *Sent:* Thursday, November 18, 2021 3:22 PM
> *To:* sbs_gems at jlab.org <sbs_gems at jlab.org>
> *Subject:* [Sbs_gems] [EXTERNAL] UV GEM HV Settings
>
>
>
> Hi Kondo and Nilanga,
>
>
>
> After we changed the resistor on UV GEM layer 0 back in October Kondo
> recommended to lower the HV a bit to monitor the GEM HV. Here is the
> logbook reference https://logbooks.jlab.org/entry/3930480. However we
> discovered this week that the voltage has never been returned to 3697 V
> since then, and we ran all this week at 3653 V. From Kondo's log it is my
> impression that he meant to only set it to 3653 V for a few hours. Is it ok
> to change to 3697 V at this point? Also with the two other UV GEMs in BB we
> also have these new dividers. Then ran all night at 3653 V with cosmics
> with no issues. Can we set those to 3697 V as well?
>
>
>
> Best,
> Sean
>
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