Difference between revisions of "New alcohol"

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If necessary, increase the proportion of Ar to give us similar max drift times to before-2-propanol runs.  What decrease in efficiency constitutes necessity?
 
If necessary, increase the proportion of Ar to give us similar max drift times to before-2-propanol runs.  What decrease in efficiency constitutes necessity?
  
Note that slight increase in Ar (few percent) would give us shorter drift times and higher gain, so we could run at lower HV.  In future years we may need to increase the HV as the chamber ages, there is very little headroom to do this (we are close to the max on the supplies) & we may need to increase the Ar at that point anyway.
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Note that slight increase in Ar (few percent) would give us shorter drift times and higher gain, so we could run at lower HV.  In future years we may need to increase the HV as the chamber ages.  Apparently the HV max limit can be adjusted on the back of the unit so that's not an issue.
  
 
Max drift times from various gas mixtures, 2125V and 1.9T
 
Max drift times from various gas mixtures, 2125V and 1.9T
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Reinhard suggested that heating the bubbler would give us less alcohol in the gas mix.
 
Reinhard suggested that heating the bubbler would give us less alcohol in the gas mix.
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Changing the gas mix would also require new Garfield tables for the time to distance tables (quick) and repeating the drift/field function fits (not so quick) https://halldweb.jlab.org/wiki/index.php/CDC_B_field

Latest revision as of 14:39, 7 November 2019

After adding 2-propanol (isopropanol) to the chamber the max drift time increased by ~50ns, and (from a quick look) the gain appears to have increased by approx 10%. See https://logbooks.jlab.org/entry/3737619.

Max drift time (for straight straws) with cosmics and no field increased from approx 630 to 670ns which is in line with Garfield simulations for 0T, 50/50 gas mix plus 0 to 1% isopropanol. With field on, the max drift time is predicted to increase from 690ns to 735ns.

(The field varies across the chamber varies, it is highest at forward angles, most of the tracks are forward and the observed max drift time with field on is 688ns. https://logbooks.jlab.org/entry/3651126 This matches Garfield for 1.9T, so using Garfield with 1% isopropanol at 1.9T gives the new estimate of 735 ns).


Concerns about the longer drift time: reduced efficiency due to greater chance of noise or out of time hits arriving before the real hit, this would be greater still when running at higher intensity. Not sure how to quantify this, not confident that simulation for higher intensity will be accurate.

Apparently it takes about 2 days to flush the mixing tank so the CDC would not be at its best for a few days (2.5?) after changing the gas mix.

Possible plan:

Run as is for the fall run, measure efficiency w HV scan, go from there. Repeat in spring at higher intensity current. Is the CDC_Efficiency plugin good enough for this?

If necessary, increase the proportion of Ar to give us similar max drift times to before-2-propanol runs. What decrease in efficiency constitutes necessity?

Note that slight increase in Ar (few percent) would give us shorter drift times and higher gain, so we could run at lower HV. In future years we may need to increase the HV as the chamber ages. Apparently the HV max limit can be adjusted on the back of the unit so that's not an issue.

Max drift times from various gas mixtures, 2125V and 1.9T

%Ar   %CO2  %2pr max drift (ns)  Gas mixer setting
49.5  49.5  1.0  735
50.5  48.5  1.0  716
51.5  47.5  1.0  706                  52/48
52.5  46.5  1.0  692                  53/47
53.5  45.5  1.0  683                  54/46

52.5/46.5/1.0 gives us max drift closest to the normal value, however the optimal HV might be a little lower. Yves reported optimum HV of 150V less for 60/40 Ar/CO2 than for 50/50 Ar/CO2. Decreasing the HV to 2100V caused the simulated max drift time to increase ~ 10ns.

Max drift times from various gas mixtures, 2100V and 1.9T

%Ar   %CO2  %2pr max drift (ns)  
52.5  46.5  1.0  701
53.5  45.5  1.0  693 

Reinhard suggested that heating the bubbler would give us less alcohol in the gas mix.

Changing the gas mix would also require new Garfield tables for the time to distance tables (quick) and repeating the drift/field function fits (not so quick) https://halldweb.jlab.org/wiki/index.php/CDC_B_field