An apparatus for studying electrical breakdown in liquid helium at 0.4 K and testing electrode materials for the SNS nEDM experiment

TL;DR

This paper presents an apparatus designed to study electrical breakdown in liquid helium at 0.4 K, demonstrating the ability to apply high electric fields and measuring resistivity, aiding the development of materials for the SNS nEDM experiment.

Contribution

The paper introduces a novel apparatus capable of applying high electric fields in liquid helium at 0.4 K and provides initial measurements of resistivity and breakdown behavior.

Findings

Fields exceeding 100 kV/cm can be applied in liquid helium at 0.4 K.

Effective volume resistivity of LHe is greater than 5×10^18 Ω·cm.

Apparatus design and operational experience are documented.

Abstract

We have constructed an apparatus to study DC electrical breakdown in liquid helium at temperatures as low as 0.4 K and at pressures between the saturated vapor pressure and $\sim$600 torr. The apparatus can house a set of electrodes that are 12 cm in diameter with a gap of $1-2$ cm between them, and a potential up to $\pm 50$ kV can be applied to each electrode. Initial results demonstrated that it is possible to apply fields exceeding 100 kV/cm in a 1 cm gap between two electropolished stainless steel electrodes 12 cm in diameter for a wide range of pressures at 0.4 K. We also measured the current between two electrodes. Our initial results, $I<1$ pA at 45 kV, correspond to a lower bound on the effective volume resistivity of LHe of $\rho_V > 5\times10^{18}$ $\Omega\cdot$cm. This lower bound is 5 times larger than the bound previously measured. We report the design, construction, and operational experience of the apparatus, as well as initial results.