[Sbs_gems] [EXTERNAL] Mixing System for GEMs

[Ezekiel Wertz]

Currently the mixing system is matching the same percentages as if the
premixed gas were being flushed through the system. The premixed Ar/CO2
bottle normally say CO2 25.0% or something like that with an uncertainty of
+/- 2% and then say the remaining concentration is Argon. The Binary Gas
Analyzer displays this as about 77/23 or 78/22 with some variance in the
signal readback.

Zeke

On Mon, Nov 8, 2021 at 12:19 PM Bogdan Wojtsekhowski <bogdanw at jlab.org>
wrote:

> Great, so it was more CO2.
> Would you match the same % as in the premixed bottles?
> ------------------------------
> *From:* Ezekiel Wertz <ewertz at email.wm.edu>
> *Sent:* Monday, November 8, 2021 12:16 PM
> *To:* Bogdan Wojtsekhowski <bogdanw at jlab.org>
> *Cc:* sbs_gems at jlab.org <sbs_gems at jlab.org>; Jack Segal <segal at jlab.org>
> *Subject:* Re: [Sbs_gems] [EXTERNAL] Mixing System for GEMs
>
> Hi Bogdan,
>
> So what it seems like to me is that the different techniques used in
> determining the concentrations of gas are different between the
> manufacturer and the gas mixing system used by Jack. This ultimately leads
> to a 2-3% difference in the gas concentration. Which is about the
> uncertainty of the premixed gas. Since the gas system was originally 75/25,
> but displays the premixed system as about 77/23 or 78/22, we originally saw
> the GEM efficiency lower even though the mixing system was operating
> properly. I think this answers your question.
>
> Zeke
>
> On Mon, Nov 8, 2021 at 12:12 PM Bogdan Wojtsekhowski <bogdanw at jlab.org>
> wrote:
>
> Looks nice. Could you summarize why the original use of the mixing system
> was
> not successful?
> ------------------------------
> *From:* Sbs_gems <sbs_gems-bounces at jlab.org> on behalf of Ezekiel Wertz <
> ewertz at email.wm.edu>
> *Sent:* Monday, November 8, 2021 12:07 PM
> *To:* sbs_gems at jlab.org <sbs_gems at jlab.org>
> *Cc:* Jack Segal <segal at jlab.org>
> *Subject:* [Sbs_gems] [EXTERNAL] Mixing System for GEMs
>
> Hi GEM folks,
>
> I have attached a plot and will describe a discussion I had with Jack this
> morning pertaining to the GEM gas mix system. So if you have questions he
> may be able to address them better. I would like to preface that the mixing
> system is not connected to the BigBite GEMs when these tests and
> manipulations were done.
>
> Recently (last couple of days) Jack was able to use the Binary Gas
> Analyzer, which I think analyzes the gas sample using a molecular
> technique. Jack would be able to provide a more accurate description of the
> technique. Whereas, the original mixing system used a mass slow control
> based off of a voltage setpoint. What he noticed is that both systems agree
> pretty well.
>
> The plot pretty much summarizes the behavior of the GEM gas system, but I
> will provide a description as well. The original gas mixing system used for
> the GEMs was properly calibrated to 75/25 or 74/26 Ar/CO2. We see this
> early on in the plot (more to the left). After this Jack then connected
> premix Ar/CO2 75/25, premix Ar/CO2 80/20, and 100% Argon. What we see is
> that with the Binary Gas Analyzer the premixed Ar/CO2 75/25 actually
> displays as closer to 77/23 or 78/22 for Ar/CO2. Then to the right of the
> plot we see that Jack has calibrated the mixing system to be fairly
> identical to the premix gas value. In other words the mixing system is now
> calibrated to the same concentrations of Ar/CO2 as the premixed gas that
> the GEM folks are more familiar with.
>
> So the gas system needs to flush for a couple of hours and it has been
> since about 10am this morning. From last week there is cosmic data using
> the premix system and GEM efficiencies are available. This afternoon we
> could switch to the mix system. Let it flush the now calibrated mixed
> Ar/CO2 through the BigBite GEMs for at least 10 hours and then some time
> this week before returning to beam operations we could collect cosmic data
> and compare it to the efficiencies with the premixed gas.
>
> If there are any comments or questions please respond to this email.
>
> Best,
> Zeke
>
>
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