Somesh Vinayak Tewari

Development and Analysis of PFN Based Compact Marx Generator Using Finite Integration Technique for an Antenna Load

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.

Particle-in-Cell Simulations of Discharge Along Gas–Solid Interface

A new computational model to understand the mechanism of discharges along the gas/solid interface at high voltage and high pressure is made based on the models of explosive electron emission, secondary emission, and neutral gas ionization by using finite-difference time domain-based particle-in-cell code. The charge particle movement at different durations is obtained at a pressure of 1 atmosphere. The profiles of phase space, the net charge density along the gap, and the effect of the dielectric on the characteristics of the gas discharge are presented. The ionization coefficient (α) and drift velocity (ve) calculated from simulation data closely match with the existing experimental results.

Computational model of discharge across a gas/solid interface at high pressure

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.

Pulsed flashover of solid dielectric materials in compressed gas environment

An experimental investigation of surface flashover characteristics of PMMA and POM is studied in compressed nitrogen gas environment with nitrogen as the background gas. The operating pressure range is from 1kg/cm2 to 4kg/cm2. It is observed that the breakdown voltage of PMMA is higher than POM owing to a higher permittivity mismatch between POM- nitrogen interface as compared to the PMMA- nitrogen interface. The reduction in spacer efficiency with pressure for PMMA is 11% as compared to POM which shows a higher reduction of 18%. This paper further emphasizes on the role of energy level and density of charge carrier trapping centers for a reduced breakdown voltage in POM as compared to PMMA.

Simulation of breakdown mechanism in high-power spark gaps filled with nitrogen gas at atmospheric pressure

A comparative computational analysis of electrical breakdown is done by introducing imperfection or void in a dielectric inside a high-voltage cavity design with nitrogen as the background gas. The simulations have been carried out using 3D particle-in-cell tools. The partial discharge (PD) causes electric field strength variations along the dielectric and ionization of the gas inside the void that lead to breakdown of the gas and plasma formation with varied particle (ions and electrons) momenta within the dielectric. The PD effects in the dielectric rupture condition with an irregular void and fissure are compared with a smaller void enclosed by the dielectric. The charged particle dynamics in dielectric and its effect on the streamer present in the outside cavity are observed.

Surface potential decay of PMMA and POM in air

Perspex (polymethyl methacrylate (PMMA)) and delrin (polyoxymethylene (POM)) are subjected to high voltages and then the surface potential decay is measured using an electrostatic voltmeter. The surface trapping parameters of PMMA are calculated using isothermal current theory and a plot between trap density and energy level is obtained. It is observed that the maximum electron and the hole traps in the surface layer of PMMA are ~1.5 × 1017 eV−1m3 and 0.8 × 1017 eV−1 m3, respectively, and the energy level of its electron and hole traps are in the range of 0.60–0.90 eV and 0.78–0.9 eV, respectively. The introduction of roughness on POM surface leads to an increase in the energy level from 0.55–0.87 eV to 0.55–0.89 eV. It is also observed that there is an increase, both in peak surface potential and time to decay in PMMA as compared to POM. This holds true for positive as well as negative dc voltages and is caused by the charge retentivity in the material resulting from the length of the polymeric chain.

Effect on electron drift velocity and ionization coefficient along a gas-solid interface

This paper presents the theoretical analysis of the variations in the drift velocity and ionization coefficient of electrons in the presence of an insulator in gases at high pressure. The model is developed taking into consideration the variation of parameters like drift velocity, ionization coefficient, transit time of travel of electron and streamer length in the presence of insulator which are responsible for flashover of insulator in gases at a reduced voltage unlike the plain gas gap conditions. Some of the parameters calculated theoretically are found to be in close agreement with the existing experimental data.

3D particle in cell simulations of spark gap discharge using Argon gas as dielectric medium

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 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 discharge. The difference between the two gases for using them as a dielectric medium in spark gaps is presented.

Optimisation of sequential triggering delay in a coaxial fast erecting Marx generator

This paper analyses the phenomena of wave erection in a coaxially arranged fast erecting MARX generator for finding the importance of delayed sequential synchronization of spark gap switches. A wave propagation model of coaxially arranged MARX generator is made. Simulation shows, that generated output voltage and energy delivered to load is not a monotonous function of delay time. Variation of output voltage with delay in triggering of sparkgap is plotted. Similar experimental setup is fabricated and tested with copper sulphate dummy load. Results are compared and discussed in the following sections of the paper.