Difference between revisions of "CDC 60 40"
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This does not look nearly as good as 50/50 gas mix. | This does not look nearly as good as 50/50 gas mix. | ||
− | Resolution is calculated as fitted drift distance - measured distance, so it is positive when the measured drift time and distance are too small. | + | Resolution is calculated as fitted drift distance - measured (interpolated) distance, so it is positive when the measured drift time and distance are too small. |
In this case they are slightly too small at small drift distance but too large at large drift distance. This could be a problem with the gas mix. For reference, plot res vs distance for tz=5,7,and 0. | In this case they are slightly too small at small drift distance but too large at large drift distance. This could be a problem with the gas mix. For reference, plot res vs distance for tz=5,7,and 0. | ||
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|[[Image:run_31842_resx20_tz8_6040.png|thumb|x250px|1975V, resolution vs hit radius]] | |[[Image:run_31842_resx20_tz8_6040.png|thumb|x250px|1975V, resolution vs hit radius]] | ||
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− | Increasing tz_add to 8ns shifts the resolution up at earlier times but it hardly moves at later times. This would probably have been obvious from the tz=0 data (below). | + | Increasing tz_add to 8ns shifts the resolution up at earlier times but it hardly moves at later times. This would probably have been obvious from the tz=0 data (below) where all the measured drift distances are too large. "Measured" drift distances are actually interpolated from a table of distance calculated for a given gas mix and a range of time measurements. So for this data I should use Garfield tables for a gas mix with faster drift velocity, ie more Ar. |
{| border="0" cellpadding="2" | {| border="0" cellpadding="2" | ||
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Suspect total flow of 60sccm might be too low for the CO2 MFC. Increase to 80sccm and repeat. Also try Garfield for different gas mixes and look at tmax. | Suspect total flow of 60sccm might be too low for the CO2 MFC. Increase to 80sccm and repeat. Also try Garfield for different gas mixes and look at tmax. | ||
+ | Measured Tmax was 573, Garfield calcs give 560ns for 60/40, 517ns for 63/37 (and 610ns for 57/43). Not sure the fitted Tmax is accurate enough to pick the gas mix given the slope at the high end of drift time histo. |
Revision as of 17:09, 11 September 2012
60/40 Ar/CO2 and cosmics, prototype horizontal
This does not look nearly as good as 50/50 gas mix. Resolution is calculated as fitted drift distance - measured (interpolated) distance, so it is positive when the measured drift time and distance are too small. In this case they are slightly too small at small drift distance but too large at large drift distance. This could be a problem with the gas mix. For reference, plot res vs distance for tz=5,7,and 0.
Increasing tz_add to 8ns shifts the resolution up at earlier times but it hardly moves at later times. This would probably have been obvious from the tz=0 data (below) where all the measured drift distances are too large. "Measured" drift distances are actually interpolated from a table of distance calculated for a given gas mix and a range of time measurements. So for this data I should use Garfield tables for a gas mix with faster drift velocity, ie more Ar.
Suspect total flow of 60sccm might be too low for the CO2 MFC. Increase to 80sccm and repeat. Also try Garfield for different gas mixes and look at tmax.
Measured Tmax was 573, Garfield calcs give 560ns for 60/40, 517ns for 63/37 (and 610ns for 57/43). Not sure the fitted Tmax is accurate enough to pick the gas mix given the slope at the high end of drift time histo.