New Readout Techniques of the DRIFT-II Detector
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The DRIFT detector is a negative ion time-projection chamber used for dark matter detection. It is unique in that it drifts negative ions instead of electrons, which limits diffusion within the detector. The detector contains a cathode and anode, separated by a potential difference of 10 kV, which provides a strong electric field and negates the need for a strong magnet to drift the ions. Currently, in the DRIFT-I detector, the anode plane (consisting of dozens of 20 micron wires) are readout to provide information about the path an event took within the detector (along the so-called x-axis). The detector also picks up track information along an arbitrarily labeled z-axis by using timing information and known drift velocities. Because the DRIFT-I detector see in x and z, it has 2 dimensional sight. In DRIFT-II, another readout technique is implemented to provide full three-dimensional sight. Sandwiching the anode plane are two grid planes. These grid planes are nearly identical to the anode plane, with the two main exceptions being the grid planes are at a more negative potential, and their wires are oriented perpendicular to the anode wires. The purpose of the grid is to provide a super-strong electric field around the anodes to create Townsend avalanche near the anodes. DRIFT-II implements readout of the grid as well as the anode. Because of the grid wires' perpendicular orientation relative to the anode, the DRIFT detector picks up an additional dimension of sight, and obtains full directionality within the detector.