A Novel UV Laser System for Electric Field Calibration in Liquid Argon Time Projection Chambers

At the core of any time projection chamber lies the electric field. The field is responsible for the separation of electron-ion pairs created during charged particle interactions as well as their transport to the readout plane. Any non-uniformity in the electric field causes distortions to a drifted ionization track, impacting the detectors spatial resolution and calorimetric capabilities. Both the spatial and calorimetric capabilities are central to the time projection chamber and provide their key advantage over other detector technologies The effect is particularly prominent in large scale liquid argon time projection chambers used for precision neutrino experiments. Sampling the detector with intrinsically straight ultraviolet laser beams while recording the distorted ionization signal provides a probe of the electric field. In this thesis the necessary hard- and software of such an ultraviolet laser system used to characterize the electric field in a liquid argon time projection chamber is outlined. Furthermore, the deployed methods to recover a spatial distortion and electric field map are described and verified against simulations. In case of the MicroBooNE detector, a map of the spatial distortion was obtained and a maximal spatial distortion of 20 ± 4 cm has been observed. Furthermore, the electric field has been reconstructed within the coverage limits of the laser system, a maximal distortion from the nominal field of 15 ± 4 % has been measured. The temporal distortion variation of the spatial distortion in drift direction has been observed to be 2.2 ± 0.3 mm over two hours. Correlations between neighboring wires suggest that these features extend up to 20 cm