Liquid Argon Dielectric Breakdown Studies with the MicroBooNE Purification System

TL;DR

This study systematically investigates the dielectric breakdown electric field in liquid argon using various electrode geometries and contamination levels, revealing a geometric dependence and the first known area dependence in liquid argon.

Contribution

It presents the first demonstration of how stressed cathode area influences breakdown electric field in liquid argon, using a dedicated cryostat and electrode geometries.

Findings

Breakdown electric field depends on electrode geometry.

First evidence of stressed cathode area effect in liquid argon.

Breakdown voltage varies with contamination levels.

Abstract

The proliferation of liquid argon time projection chamber detectors makes the characterization of the dielectric properties of liquid argon a critical task. To improve understanding of these properties, a systematic study of the breakdown electric field in liquid argon was conducted using a dedicated cryostat connected to the MicroBooNE cryogenic system at Fermilab. An electrode sphere-plate geometry was implemented using spheres with diameters of 1.3 mm, 5.0 mm, and 76 mm. The MicroBooNE cryogenic system allowed measurements to be taken at a variety of electronegative contamination levels ranging from a few parts-per-million to tens of parts-per- trillion. The cathode-anode distance was varied from 0.1 mm to 2.5 cm. The results demonstrate a geometric dependence of the electric field strength at breakdown. This study is the first time that the dependence of the breakdown field on stressed cathode area has been shown for liquid argon.