Purity monitoring for ProtoDUNE-SP

The Deep Underground Neutrino Experiment (DUNE) is a next-generation long-baseline neutrino oscillation experiment based on liquid argon time projection chamber (LArTPC) technology. DUNE's single-phase (SP) prototype ProtoDUNE-SP (PD-SP) at CERN finished its two-year Phase-1 running in July 2021, successfully collected test-beam and cosmic ray data. A key aspect of LArTPC calibration is the lifetime of drift electrons, which corrects the charge attenuation caused by drift electrons captured by impurities. A purity monitor is a miniature TPC measuring the lifetime of electrons generated from the photocathode via the photoelectric effect. It enables continuous monitoring of the detector status, especially when filling the cryostat and when liquid argon recirculation systems operate. The purity monitoring system in ProtoDUNE-SP Phase-1 (PD-SP-I) monitored liquid argon purity throughout its entire lifetime. It is essential to the experiment's successful commissioning, operation, and data taking. I will discuss the design, implementation, and results of purity monitors in PD-SP-I and future plans.