Search

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 elaborates the effect of unmatched stored energy in high-voltage high-energy pulsed power systems. High-voltage insulation failure of KALI system is analyzed thoroughly for its occurrence. According to the simulations and analysis energy mismatch of MARX generator and Blumlein transmission line is found to be the most significant cause for high-voltage failure of the system. MARX generator and Blumlein of KALI are redesigned to attain better energy balance at same voltage level. Observations, simulation and analytical results are illustrated in the following sections.

We report a direct observation of the microsecond time scale combustion of aluminum realized in underdamped electrical explosions of aluminum wires in the water environment. Experiments were conducted using a pulse power generator delivering a ≤200 kA current amplitude within an ∼1 μs rise-time. Time-resolved spectroscopy was applied to obtain the spectrum of AlO oxide absorption bands, and the temperature of oxides was determined. The results show that decreasing the wire diameter and increasing the discharge current density allow one to decrease the time delay in the appearance of AlO absorption bands to ≤1 μs with respect to the beginning of the wire explosion and significantly increase the rate of aluminum combustion up to ∼1.3 × 103 g/s.

Using streak images of underwater electrically exploding copper, aluminum, and tungsten wires (current densities of 107–108 A/cm2 and energy density deposition of 10–50 kJ/g) and generated weak shocks, the onset of each phase transition, its duration, and the time when the wire explosion occurred were determined. The measured discharge current and resistive voltage were used to calculate the energy and energy density deposition. Using the discharge current waveform and the onset of the strong shock wave, the specific action integral was calculated and compared with published data. The thermodynamic parameters during the wire explosion were calculated using one-dimensional magneto-hydrodynamic simulations coupled with equations of state for water, copper, and aluminum. It was shown that the onset times of weak shocks, in general, cannot be related to the melting or the evaporation of the entire wire.Using streak images of underwater electrically exploding copper, aluminum, and tungsten wires (current densities of 107–108 A/cm2 and energy density deposition of 10–50 kJ/g) and generated weak shocks, the onset of each phase transition, its duration, and the time when the wire explosion occurred were determined. The measured discharge current and resistive voltage were used to calculate the energy and energy density deposition. Using the discharge current waveform and the onset of the strong shock wave, the specific action integral was calculated and compared with published data. The thermodynamic parameters during the wire explosion were calculated using one-dimensional magneto-hydrodynamic simulations coupled with equations of state for water, copper, and aluminum. It was shown that the onset times of weak shocks, in general, cannot be related to the melting or the evaporation of the entire wire.

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.

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.

Summary form only given. This paper deals with the discharge along the surface of angled insulators in compressed gases using 3D finite difference particle-in-cell simulation. The simulation is carried in pure nitrogen at atmospheric pressure. The ionization of neutral atoms of nitrogen takes place by electron impact leading to production of positive ions and secondary electrons. The ionization cross sections of electrons with neutral gas molecules are taken as function of electron energy. The pulse rise time is 5ns with pulse duration of 50ns. The spacer angle `θ' is measured between the inclined surface and line vertical to the electrode. The angle is positive when narrow end is connected to the anode and negative otherwise. The positive spacer angle shows a reduced discharge voltage for a 20mm gap length which is close to the discharge voltage for cylindrical insulators. The negative spacer angle shows a discharge voltage close to the bulk gas gap condition. This is explained by a reduction in the momentum profile of electrons for positive spacer angle which aids in earlier emission of electrons and the discharge path followed is same as that for cylindrical insulators whereas an increase in momentum for negative spacer angle gives a longer discharge path and hence condition close to the bulk gas gap. This finds application in the design of high voltage insulators subjected to impulse voltages.

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.

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.