[Sbs_gems] [EXTERNAL] Mixing System for GEMs

[Jack Segal]

Just to be clear, the BGA uses standing ultrasonic waves in a cavity to determine the ratio of a two gas mixture.
It is a Stanford Research Systems model BGA244.

On 11/8/2021 12:22 PM, Ezekiel Wertz wrote:
> 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 <mailto: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 <mailto:ewertz at email.wm.edu>>
>     *Sent:* Monday, November 8, 2021 12:16 PM
>     *To:* Bogdan Wojtsekhowski <bogdanw at jlab.org <mailto:bogdanw at jlab.org>>
>     *Cc:* sbs_gems at jlab.org <mailto:sbs_gems at jlab.org> <sbs_gems at jlab.org <mailto:sbs_gems at jlab.org>>; Jack Segal <segal at jlab.org <mailto: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 <mailto: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 <mailto:sbs_gems-bounces at jlab.org>> on behalf of Ezekiel Wertz <ewertz at email.wm.edu <mailto:ewertz at email.wm.edu>>
>         *Sent:* Monday, November 8, 2021 12:07 PM
>         *To:* sbs_gems at jlab.org <mailto:sbs_gems at jlab.org> <sbs_gems at jlab.org <mailto:sbs_gems at jlab.org>>
>         *Cc:* Jack Segal <segal at jlab.org <mailto: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
> 

-- 
John(Jack) Segal
Halls A and C Spectrometer Support Manager
Thomas Jefferson National Accelerator Facility
12000 Jefferson Avenue
Suite 12
Newport News, VA 23606-4486
Phone: (757) 269-7242
Cell: (757) 320-9977