Speaker
Description
Liquid argon time projection chambers (LArTPCs) such as the Deep Underground Neutrino Experiment (DUNE) must maintain high argon purity as electronegative impurities can capture drift electrons, degrading signal quality and raising the detection threshold of particle energy depositions. A purity monitor is a miniature TPC that measures the electron lifetime by comparing the charge collected from an electron source between a cathode and anode across a drift distance for the purpose of calibrating detector response. The electron source is traditionally a gold photocathode excited by UV light from an external xenon flash lamp delivered via optical fibers into the detector, but a purity monitor with a new bismuth-207 radioactive electron source was recently tested at ProtoDUNE for continuous purity monitoring. The production of both purity monitor models for the full DUNE far detectors has begun, and each of these will be tested at a liquid argon test facility at UC Irvine. This facility uses liquid nitrogen to condense argon gas to submerge the purity monitors and can continuously recirculate argon through a filter to achieve the necessary purity. The custom filter uses a molecular sieve to absorb water and a copper catalyst to remove oxygen, the leading electronegative impurity. These designs along with extensive quality control tests will ensure detailed monitoring of DUNE detector conditions throughout the cryostat volumes and throughout the experiment’s operation.