Difference between revisions of "New alcohol"
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Max drift times (ns) from various gas mixtures and 2125V: | Max drift times (ns) from various gas mixtures and 2125V: | ||
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| − | %Ar %CO2 % | + | %Ar %CO2 %2p max drift time at 1.9T |
49.5 49.5 1.0 735 | 49.5 49.5 1.0 735 | ||
50.5 48.5 1.0 716 | 50.5 48.5 1.0 716 | ||
Revision as of 13:46, 6 November 2019
After adding 2-propanol (isopropanol) to the chamber the max drift time increased by ~50ns, 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 be mostly inoperable for 2d after changing the gas mix.
Possible options:
Run as is for the fall run, measure efficiency w HV scan, go from there. Repeat in spring at higher intensity current.
Increase the proportion of Ar to give us similar max drift times to before-2-propanol runs. Fill this in with Garf results.
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) so we may need to increase the Ar at that point anyway.
Max drift times (ns) from various gas mixtures and 2125V:
%Ar %CO2 %2p max drift time at 1.9T 49.5 49.5 1.0 735 50.5 48.5 1.0 716 51.5 47.5 1.0 706 52.5 46.5 1.0 692 53.5 45.5 1.0 683
52.5/46.5/1.0 gives us max drift closest to the normal value, however the optimal HV might be a little lower.
