Procuring 50 Tonnes of Underground Argon for DS-20k

The DarkSide-50 (DS-50) two-phase liquid argon (LAr) detector has been searching for weakly interacting massive particle (WIMP) dark matter for the past four years, and during the last three years has been successfully operating the detector with argon that was extracted from underground CO₂ wells in Colorado, USA. This source of argon has been long shielded from cosmic rays entering Earth’s atmosphere, and has been proven to have a lower concentration of the cosmogenically produced isotope of ³⁹Ar that beta decays with an endpoint energy that causes the beta spectrum to entirely cover the LAr WIMP search region. A 70-day exposure of the underground argon (UAr) inside DS-50 demonstrated that the UAr extracted from Colorado contains a factor greater than 1400 less ³⁹Ar, compared to argon separated from the air in Earth’s atmosphere. This large reduction in ³⁹Ar opens the door for the construction of much larger two-phase LAr detectors that can be used for the direct detection of WIMP dark matter, as well as other rare-event searches. This talk will focus on the details of a new project called Urania, aiming to extract up to 250 kg/day of UAr from the same source of gas used to extract the UAr for DS-50. This effort will procure 50 tonnes of UAr for use in a 20-tonne fiducial volume detector called DarkSide-20k, which is set to begin operations in 2021.

This presentation was used for the Low-Radioactivity Underground Argon Workshop held at Pacific Northwest National Laboratory in Richland, Washington on March 19 - 20, 2018.