Gas contamination and mitigation in a 100 m$^3$ / 10 bar argon TPC with optical readout: a viability study

TL;DR

This study evaluates the feasibility of gas contamination control and mitigation strategies in a large argon TPC with optical readout, crucial for neutrino and rare event detection, focusing on material choices and impurity management.

Contribution

It demonstrates the conceptual viability of optical readout in a large argon TPC, analyzing gas distribution, outgassing, and impurity mitigation techniques for the DUNE Near-Detector.

Findings

Contaminant levels can be controlled within a week after filling.

Fresh gas injection effectively maintains impurity levels within operational limits.

Material choices and distributor design are critical for impurity mitigation.

Abstract

Gaseous Optical Time Projection Chambers (OTPCs) aimed at Neutrino Physics and Rare Event Searches will likely exceed the tonne scale during the next decade. This will make their performance sensitive to gas contamination levels as low as 100 ppb, that is challenging at room temperature due to outgassing from structural materials. In this work we discuss gas distribution and impurity mitigation in a 5 m-length/5 m-diameter 10 bar TPC filled with Ar/CF$_4$ admixed at 99/1 per volume (1.75 tonne), loaded with technical plastics in order to enhance light collection and readout. Different distributor topologies, outgassing and flow rates are discussed. Specifically, our work is aimed at illustrating the conceptual viability of the optical readout of ND-GAr's TPC (within the DUNE Near-Detector complex), in terms of material compatibility. For our proposal, with perforated distributors aligned with the electric field, and under realistic assumptions, the concentration of contaminants can be controlled within a week after chamber filling. In the case of N$_2$, injection of fresh gas at %-level seems to represent the safest strategy to keep the concentration within operability limits.