Electronic transport coefficients and electric breakdown in condensed helium

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 influencing 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 theoretical findings are compared with available experimental data. For liquid helium the long-standing fundamental 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 experimental data allows also answering the question of how the voltage application duration and contaminants affect the breakdown characteristics of liquid helium.