A Study of Dielectric Breakdown Along Insulators Surrounding Conductors in Liquid Argon

TL;DR

This study systematically measures dielectric breakdown voltages along insulators in liquid argon to inform high voltage feedthrough design, revealing permittivity effects and independence from insulator length.

Contribution

It provides new experimental data on breakdown behavior in liquid argon and introduces a model to predict breakdown mechanisms for improved high voltage component design.

Findings

Breakdown voltage depends on material permittivity.

Breakdown voltage is independent of insulator length.

A model for breakdown mechanism is proposed.

Abstract

High voltage breakdown in liquid argon is an important concern in the design of liquid argon time projection chambers, which are often used as neutrino and dark matter detectors. We have made systematic measurements of breakdown voltages in liquid argon along insulators surrounding negative rod electrodes where the breakdown is initiated at the anode. The measurements were performed in an open cryostat filled with commercial grade liquid argon exposed to air, and not the ultra-pure argon required for electron drift. While not addressing all high voltage concerns in liquid argon, these measurements have direct relevance to the design of high voltage feedthroughs especially for averting the common problem of flash-over breakdown. The purpose of these tests is to understand the effects of materials, of breakdown path length, and of surface topology for this geometry and setup. We have found that the only material-specific effects are those due to their permittivity. We have found that the breakdown voltage has no dependence on the length of the exposed insulator. A model for the breakdown mechanism is presented that can help inform future designs.