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The presence of spacer in a spark-gap system leads to a reduction in breakdown voltage. This paper studies the effect of spacer surface profile and surface protrusions on the breakdown voltage in compressed gases. Different spacer profiles comprising of conical angled insulators, bush-bar insulators, and double ended frustum insulators are used to study the effect of spacer profile on spacer efficiency under nanosecond pulsed voltage using particle-in-cell simulation. The effect of protrusions on the surface of the insulators is modeled to study the effect of teeth height on spacer efficiency. An increase in spacer efficiency from 86% in case of cylindrical spacer to 97% with negative angled and bush bar spacer is observed for a 20-mm spacer length placed between the spark gap electrodes with nitrogen as background gas.

Relativistic electron beam generation studies have been carried out in LIA-400 system through explosive electron emission for various cathode materials. This paper presents the emission properties of different cathode materials at peak diode voltages varying from 10 to 220 kV and at peak current levels from 0.5 to 2.2 kA in a single pulse duration of 160-180 ns. The cathode materials used are graphite, stainless steel, and red polymer velvet. The perveance data calculated from experimental waveforms are compared with 1-D Child Langmuir formula to obtain the cathode plasma expansion velocity for various cathode materials. Various diode parameters are subject to shot to shot variation analysis. Velvet cathode proves to be the best electron emitter because of its lower plasma expansion velocity and least shot to shot variability.

This paper presents the design and development of a compact Marx generator based on pulse forming network (PFN) along with a peaking capacitor rated at 300 kV and 64 J. Proposed scheme consists of identical PFNs connected across the charging and grounding resistors according to the Marx generator scheme. Modular construction of the Marx generator is useful in altering the stage capacitance to obtain varying pulse rise time and wave shapes at the output. A peaking capacitor connected at the output of the Marx generator significantly improves the rise time from 25 to 5 ns suitable for driving an antenna load. The effect of peaking capacitor on the intensity of far-field radiation is simulated using finite integration technique for a distance of 15, 20, 30, 40, and 50 m and the results are presented and discussed.

Summary form only given. This paper presents PIC simulations of spark gap discharge, filled with Argon gas at atmospheric pressure. The rogowsky profile electrodes having an inter-electrode gap distance of 20mm were used in this study. The model is based on explosive electron emission from cathode, secondary emission and neutral Argon gas ionization. The phase space profiles, current density, ionization, temperature and velocity of electron plots are presented. Results show that some simulations are in good agreement with existing experimental data. The simulation data of argon discharge was also compared with our previous work of nitrogen gas discharge1. The difference between the two gases for using them as a dielectric medium in spark gaps is presented.

A numerical model employing FDTD based particle-in-cell code (PIC) is used to study the discharge mechanism across a gas /solid interface. The simulation is carried out with and without an insulator in the anode cathode gap at a pressure of latmosphere and a ramp voltage with a rise time of 5ns and pulse duration of 50ns is used as the input pulse. The profiles of electron densities, avalanche growth, phase profile of electrons, and the gap voltage are calculated with and without an insulator to study the mechanism of discharge in presence of an insulator. Spacer efficiency of 81% is obtained which closely agrees with the existing experimental data.

The design, development and commissioning of 1 MV pulsed electron accelerator producing Flash X-Rays is described in this paper. This pulsed power system is based on bipolar MARX generator and Blumlein followed by Explosive electron emission diode assembly. The peak pulsed power is ~ 30 GW. The electron energies in the range of 400 keV to 1030 keV are produced and delivered to experimental load of Industrial diode. Electrons are emitted from a stainless steel ring at ground potential by explosive field emission and bombard the anode tungsten pin for flash X-rays generation. The relativistic electron beam has been simulated within the diode chamber and pattern shows the beam propagation. Imaging plates are used to characterize the source size and optimization has been reported.