Construction, Testing and Characterization of Vertical Drift Chambers for Qweak

Qweak is an experiment set to take place at Jefferson Lab that will put the Standard Model to the test by measuring the weak charge of the proton by precisely measuring the parity-violating asymmetry of elastic proton-electron scattering. Ver- tical Drift Chambers, which will momentum analyze events that take place, will be key to the tracking system of Qweak. A vertical drift chamber was constructed and conditioned by applying high voltage to the chamber. After conditioning, the current that the chamber would draw at 3.55kV began to spike to 10.3?A and therefore we were cautious to go above this voltage level when testing the chamber. The efficiency of the chamber was measured using cosmic rays and a 90Sr source. Using cosmic rays, the efficiency of the chamber was (95.3 � 1.3)% at 3.5kV, whereas when using the 90Sr source, the efficiency of the chamber was (81.3 � 1.9)% at 3.5kV. However, it was discovered that these efficiencies were contaminated by background noise that was being picked up by the electronic equipment used to measure the efficiency. After eliminating this background noise, the efficiency of the chamber was again measured, yet it was not at an operating efficiency, which is typically on the order of 99 - 100%. It appeared that the chamber needed to be able to handle larger voltages, however, this was not possible due to the amount of current that the chamber would draw at these larger voltages. It was discovered that the bottom wire frame was the source of the current at these large voltages, so we decided to disassemble the chamber and replace this wire frame. The chamber was then reassembled and is currently being conditioned.