Spatial and Temporal Evaluations of the Liquid Argon Purity in ProtoDUNE-SP

TL;DR

This paper evaluates the liquid argon purity in ProtoDUNE-SP, introducing a new muon-based measurement method, and finds that the electron lifetime exceeds 30 ms over weeks, with purity varying by position.

Contribution

It introduces a novel method to measure argon purity using muons crossing both drift volumes in ProtoDUNE-SP.

Findings

Electron lifetime exceeded 30 ms over weeks.

Purity measurements from monitors and muons are consistent.

Argon purity varies with position in the detector.

Abstract

Liquid argon time projection chambers (LArTPCs) rely on highly pure argon to ensure that ionization electrons produced by charged particles reach readout arrays. ProtoDUNE Single-Phase (ProtoDUNE-SP) was an approximately 700-ton liquid argon detector intended to prototype the Deep Underground Neutrino Experiment (DUNE) Far Detector Horizontal Drift module. It contains two drift volumes bisected by the cathode plane assembly, which is biased to create an almost uniform electric field in both volumes. The DUNE Far Detector modules must have robust cryogenic systems capable of filtering argon and supplying the TPC with clean liquid. This paper will explore comparisons of the argon purity measured by the purity monitors with those measured using muons in the TPC from October 2018 to November 2018. A new method is introduced to measure the liquid argon purity in the TPC using muons crossing both drift volumes of ProtoDUNE-SP. For extended periods on the timescale of weeks, the drift electron lifetime was measured to be above 30 ms using both systems. A particular focus will be placed on the measured purity of argon as a function of position in the detector.