[Sbs_gems] [EXTERNAL] Mixing System for GEMs

[Ezekiel Wertz]

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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