In this thesis certain aspects of the vacuum breakdown development are studied both experimentally and by numerical simulations. We start with investigations of the model of oscillatory development of electrical breakdown (Mazurek, 1988), which was based on observation of light pulses in the cathode luminosity with a regular repetition rate about 5ns/pulse. By high time resolution measurements we obtain data about transient behaviour of several physical variables (gap current, gap voltage, light emission from the gap, X-ray intensity) during breakdown development. Then we consider possibility of oscillations in electron beam current due to the virtual cathode formation. The measured data and the discussion of virtual cathode suggest that the model of oscillatory development of electrical breakdown should be discarded.Then the parameters of electron beam emitted during vacuum breakdown are calculated rigorously by tracing electron trajectories in the self-consistent electric field. The exact formulae for gap perveance are obtained for typical gap geometries. The practical model for transient anode heating is developed which includes penetration and energy deposition of electrons into the anode. Perveance and anode heating model are implemented in a PSPICE circuit model of a breaking vacuum gap. Simulations performed by the circuit model of vacuum gap are compared to the measured gap voltage and current waveforms and a reasonable agreement is found.The influence of electrode geometry, gap length and electrode material on voltage collapse is studied experimentally and then analyzed by performing circuit simulations based on the aforementioned circuit model. It is shown that uniform field gaps have faster voltage collapse due to their larger perveance compared to point-plane gaps. Extremely long voltage fall times in the case of point anode are explained by invoking braking of the cathode plasma emissive surface.Finally, certain aspects of plasma dynamics, not directly measured, are also analyzed by circuit simulations. It is determined that anode heating by an electron beam is not fast enough to produce plasma out of the anode material, and it is suggested that anode plasma is created mainly by electron impact ionization of the desorbed gas. Circuit simulations also suggest that inherent scattering in voltage fall times can be explained by inherent scattering in the expansion velocity of the cathode plasma, which stems from the stochastic behaviour of the processes of the cathode spot creation.
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