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Xe-CO 2 Stability Chiho Wang Duke University. Setup. X-ray aperture limits active region ~ 6-7cm on straw. 0.002” Cu foil reduced X-ray intensity to ~0.1uA/cm Only 1 pair of ASD sockets are active to draw current. Scan along straw at 8cm intervals.
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Xe-CO2 Stability Chiho Wang Duke University
Setup • X-ray aperture limits active region ~ 6-7cm on straw. • 0.002” Cu foil reduced X-ray intensity to ~0.1uA/cm • Only 1 pair of ASD sockets are active to draw current. • Scan along straw at 8cm intervals. • At each location, raise HV from 1550V to 1750V at 25V step, 20 sec interval. • Record current & # of Trips.
Observation • Most ASD HV trip at mid wire support location. • Some ASD HV trip at end wire support. • After several hours of “burning” at the wire support, it gets more stable and less likely to trip • ASD 28-33 were scanned many times with Ar-CO2 before taking Xe data. They are obviously more stable. • In the case of Ar-CO2, X-ray also triggers a self-sustained current draw that lasts for several hours even after X-ray is turned off. This contributes to an increase of current draw when X-ray passes through mid wire support. This current, however, also dies out after burning.
Summary • Xe-CO2 is stable at 1750V with 0.3uA/cm local rate • Mid wire support tends to be unstable in the beginning of the chamber operation, but can be improved with “burning”. • Some end wire supports also show the same instability but not as often as mid wire support.
