[Sbs_gems] [EXTERNAL] UV GEM HV Settings

Thu Nov 18 17:59:36 EST 2021

Sean,
Beside the HV scan of the new layer, you are right, that we need clear evidence of efficiency drop before deciding to go for higher HV. Current drop itself is not necessarily equivalent to efficiency drop.

Other things to look at is the ADC distribution (it will be clearer module by module and not layer by layer to avoid any smearing)  If there is significant gain drop, you will see it in ADC distribution as well. You can also look at average cluster size (here again, it is better to look at it module by module)

There are many things that can give you indication that your efficiency might be dropping beside just plan track-based efficiency. In a complex situation like this, all these information are useful and needed together before one should decide to increase the HV because of efficiency drop. GEM experts needs o be looking at all these consistently

Analyzing these information individually is not necessarily the best approach. Also having these data for layers that are made of several modules might also be misleading

Best regards
Kondo

From: Andrew Puckett <puckett at jlab.org>
Sent: Thursday, November 18, 2021 5:24 PM
To: Jeffas, Sean (sj9ry) <sj9ry at virginia.edu>; Gnanvo, Kondo (kg6cq) <kg6cq at virginia.edu>
Cc: Holly Szumila-Vance <hszumila at jlab.org>; Liyanage, Nilanga K (nl8n) <nl8n at virginia.edu>; sbs_gems at jlab.org
Subject: Re: [Sbs_gems] [EXTERNAL] UV GEM HV Settings

I think we should do a quick HV scan of the new layer at low luminosity, say 1 uA LH2. The efficiency calculation is going to be more reliable there. Then we can quickly see where we stand and if we are well below the plateau.

From: Sean Jeffas <sj9ry at virginia.edu<mailto:sj9ry at virginia.edu>>
Date: Thursday, November 18, 2021 at 4:47 PM
To: Gnanvo, Kondo (kg6cq) <kg6cq at virginia.edu<mailto:kg6cq at virginia.edu>>
Cc: Holly Szumila-Vance <hszumila at jlab.org<mailto:hszumila at jlab.org>>, Andrew Puckett <puckett at jlab.org<mailto:puckett at jlab.org>>, Liyanage, Nilanga K (nl8n) <nl8n at virginia.edu<mailto:nl8n at virginia.edu>>, sbs_gems at jlab.org<mailto:sbs_gems at jlab.org> <sbs_gems at jlab.org<mailto:sbs_gems at jlab.org>>
Subject: Re: [Sbs_gems] [EXTERNAL] UV GEM HV Settings
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<mailto: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<mailto: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<mailto:puckett at jlab.org>>; Liyanage, Nilanga K (nl8n) <nl8n at virginia.edu<mailto:nl8n at virginia.edu>>; Jeffas, Sean (sj9ry) <sj9ry at virginia.edu<mailto:sj9ry at virginia.edu>>; sbs_gems at jlab.org<mailto: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<mailto:sbs_gems-bounces at jlab.org>> on behalf of Andrew Puckett <puckett at jlab.org<mailto:puckett at jlab.org>>
Date: Thursday, November 18, 2021 at 3:43 PM
To: "Liyanage, Nilanga K (nl8n)" <nl8n at virginia.edu<mailto:nl8n at virginia.edu>>, "Jeffas, Sean (sj9ry)" <sj9ry at virginia.edu<mailto:sj9ry at virginia.edu>>, "sbs_gems at jlab.org<mailto:sbs_gems at jlab.org>" <sbs_gems at jlab.org<mailto: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<mailto:sbs_gems-bounces at jlab.org>> on behalf of Liyanage, Nilanga K (nl8n) <nl8n at virginia.edu<mailto:nl8n at virginia.edu>>
Date: Thursday, November 18, 2021 at 3:30 PM
To: Jeffas, Sean (sj9ry) <sj9ry at virginia.edu<mailto:sj9ry at virginia.edu>>, sbs_gems at jlab.org<mailto:sbs_gems at jlab.org> <sbs_gems at jlab.org<mailto: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<mailto:sbs_gems-bounces at jlab.org>> on behalf of Sean Jeffas <sj9ry at virginia.edu<mailto:sj9ry at virginia.edu>>
Sent: Thursday, November 18, 2021 3:22 PM
To: sbs_gems at jlab.org<mailto:sbs_gems at jlab.org> <sbs_gems at jlab.org<mailto: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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