Electronic transport coefficients and electric breakdown in condensed helium

Abstract

The kinetic Boltzmann equation is applied to determine the electron energy distribution function in condensed helium over a wide range of pressures and temperatures. Account is taken of all the effects influ encing the electron kinetics in dense media. The electron multiplication rates and basic electron transport coefficients in condensed helium at atmospheric and elevated pressures have been determined. Starting from the streamer theory, the limiting breakdown characteristics of condensed helium are calculated. The theoret ical findings are compared with available experimental data. For liquid helium the long standing fundamen tal problem is first solved of the intrinsic dielectric strength determined exclusively by the electron processes in a liquid itself rather than in gaseous bubbles formed at the prebreakdown stage. Comparison with experi mental data allows also answering the question of how the voltage application duration and contaminants affect the breakdown characteristics of liquid helium.

A study of DC electrical breakdown in liquid helium through analysis of the empirical breakdown field distributions

“…1 Studying the behavior of LHe under a strong electric field may be of interest in understanding electronic properties of condensed helium. 2 More recently, the study of electrical breakdown of LHe is motivated by the importance of superfluid LHe as a medium in which experiments in nuclear, particle, and astroparticle physics are performed, along with other noble liquids, in particular LAr and LXe. 3 For some experiments, the application of a high electric field is necessary.…”

“…These observations are therefore presumed to be the result of the following process: (1) Field emission of electrons occurs on a rough surface because of extremely high local fields at sharp asperities. (2) This causes local heating, which in turn results in vapor bubble formation leading to electron multiplication and vapor growth proceeding together. (3) Breakdown is then the result of a vapor column extending to the anode.…”

“…4 The experiment will be performed inside a bath of LHe at approximately 0.4 K, and large-area electrodes (61 cm × 30 cm) will provide an electric field of up to ∼75 kV/cm inside the experimental volume. Because the sensitivity of the experiment is directly proportional to the strength of this applied field, it is of critical importance to establish the following: (1) the highest electric field that can be sustained stably; (2) how the breakdown depends on factors such as the pressure and temperature of LHe, the electrode material and surface condition, and the size of the system (the electrode area and/or the size of the gap between electrodes); and…”