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In this article, a self-breakdown repetitive gap switch based on the graphite electrodes with surface modified by TiC is investigated to improve the scattering of the breakdown voltage. The self-breakdown repetitive gap switch was experimentally studied with the graphite electrodes and two kinds of TiC modified graphite electrodes (hereinafter referred to as TiC-I electrodes and TiC-II electrodes). Results show that the scatterings of the breakdown voltages of the graphite, TiC-I and TiC-II electrodes were 2.49%, 1.80%, and 1.54%, respectively. Compared with the graphite electrodes, the mass losses of TiC-I and TiC-II electrodes are reduced by 50% and 68%. The influence of electrode surface morphology on the switch stability is analyzed based on the mechanism of switch conduction process. Compared with the graphite electrodes, the electric field amplification coefficients of TiC-I and TiC-II electrodes are more evenly distributed, which leads to the more evenly distributed field emission current density. Thus, the breakdown areas of TiC-I and TiC-II electrodes are smaller and the gas breakdown processes are more stable than those of the graphite electrodes, resulting in smaller scattering of the breakdown voltage. The method that decreases the scattering of the breakdown voltage and reduces the mass loss of the electrodes by modifying graphite electrodes surface can greatly improve the stability of the switch, which is of significance to the application of the switch in the compact, long time stable operation of high-power pulse power devices. [ABSTRACT FROM AUTHOR]

Unlike planar diodes, separate research of the axial and radial plasma expansion velocities is difficult for magnetically insulated coaxial diodes. Time-resolved electrical diagnostic which is based on the voltage-ampere characteristics has been employed to study the temporal evolution of the axial and radial cathode plasma expansion velocities in a long pulsed magnetically insulated coaxial diode. Different from a planar diode with a “U” shaped profile of temporal velocity evolution, the temporal evolution trend of the axial expansion velocity is proved to be a “V” shaped profile. Apart from the suppression on the radial expansion velocity, the strong magnetic field is also conducive to slowing down the axial expansion velocity. Compared with the ordinary graphite cathode, the carbon velvet and graphite composite cathode showed superior characteristics as judged by the low plasma expansion velocity and long-term electrical stability as a promising result for applications where long-pulsed and reliable operation at high power is required. [ABSTRACT FROM AUTHOR]