IONIZATION PHENOMENON IN HIGH-DENSITY GASEOUS AND LIQUID ARGON IN CORONA DISCHARGE EXPERIMENTS

Experimental investigations of corona discharge in Ar for a wide regio n of fluid density from a rare gas up to a liquid have been carried ou t. Corona current has been observed for a point cathode voltage above the threshold value V-s. Values of V-s have been measured for a wide r ange of fluid density N and for different cathode radii r(p). The obta ined dependences of V-s(N, r(p)) on N and r(p) have been analysed usin g the Townsend-Meek breakdown criterion. For low-density gas the calcu lations of V-s have been carried out by using universal data on ioniza tion coefficient alpha(gas)/N(E/N). The data of V-s for low-density ga s are in good agreement with these calculations. Deviation from the 'g aseous' dependence has been obtained in measurements carried out with a continuous increasing of the fluid density. The onset corona voltage in dense supercritical gas and in liquid is appreciably smaller than the values calculated from the gaseous Paschen curve. To explain this disagreement a model of impact ionization in liquid was developed. An assumption was made that inelastic energy losses of fast electrons by excitation of atoms without their ionization are absent in liquid. The expression for the ionization coefficient in liquid Ar alpha(liq)/N(E /N) has been obtained and it was used for calculation of V-s in liquid . The calculated values are in agreement with the experimental data ob tained in liquid Ar.