D. D. P. Kumar

Characterization and analysis of a pulse power system based on Marx generator and Blumlein.

A pulse power system (1 MV, 50 kA, and 100 ns) based on Marx generator and Blumlein pulse forming line has been studied for characterization of a general system. Total erected Marx inductance and series resistance are calculated from modular testing of Marx generator and testing of Marx generator with Blumlein. The complete pulse power system has been tested with the termination of a liquid resistor load for finding the Blumlein characteristic impedance. Equivalent electrical circuits during the charging and discharging of the Blumlein are constructed from the characterized parameters of the system. These equivalent circuits can be used in the analysis of prepulse voltage and droop in the flat top of the main pulse in the pulse power systems based on Marx generator and Blumlein.

Intense relativistic electron beam generation and prepulse effect in high power cylindrical diode

Intense gigawatt relativistic electron beam has been generated in a high power cylindrical diode in the presence of prepulse. A bipolar prepulse voltage, recorded at the diode, varies both in amplitude and time duration with the Marx generator voltage. It was found that only at the accelerating gap ⩽1.65cm there is some shot to shot variation in the diode voltage and current for the same Marx generator voltage. The anode and cathode plasma expansion velocities were calculated using the perveance data. The plasma expands at 5cm∕μs for 1.85cm radial anode-cathode gap and the plasma velocity decreases for smaller gap. It was found that the effect of the prepulse is less pronounced in the cylindrical diode as compared to planar diode that allows one operation of the cylindrical diode with the gap ⩽1.85cm.

Impedance collapse and beam generation in a high power planar diode

Summary form only given. Intense relativistic electron beam generation studies were carried out in a planar diode configuration to investigate the effect of the plasma expansion on the impedance characteristics of the diode. The diode voltage and current waveforms were analyzed with the bipolar space-charge limited flow model. The anode and cathode plasma expansion velocities were calculated using the perveance data. The plasma expands at 9.5 cm/mus for 31 mm anode-cathode gap and the plasma velocity decreases for smaller gap. It was found that the electron emission is more uniform for 25 mm anode-cathode gap as compared to 31 mm gap. Effect of a nylon sheet on the anode plate has been studied with respect to the impedance characteristic of the diode. It was found that the plasma expand with a faster velocity in the presence of nylon sheet on anode.

A design approach for systems based on magnetic pulse compression

A design approach giving the optimum number of stages in a magnetic pulse compression circuit and gain per stage is given. The limitation on the maximum gain per stage is discussed. The total system volume minimization is done by considering the energy storage capacitor volume and magnetic core volume at each stage. At the end of this paper, the design of a magnetic pulse compression based linear induction accelerator of 200 kV, 5 kA, and 100 ns with a repetition rate of 100 Hz is discussed with its experimental results.

Analysis of temporal jitter in a copper vapor laser system

Temporal jitter in a magnetic pulse compression based copper vapor laser (CVL) system is analyzed by considering ripple present in the input dc power supply and ripple present in the magnetic core resetting power supply. It is shown that the jitter is a function of the ratio of operating voltage to the designed voltage, percentage ripple, and the total propagation delay of the magnetic pulse compression circuit. Experimental results from a CVL system operating at a repetition rate of 9 kHz are presented.

Prepulse Suppression on a High-Power Electron Beam Accelerator Using a Dielectric Cathode Holder

Intense gigawatt relativistic electron beam generation studies were carried out with a Perspex cathode holder. Purpose of the dielectric cathode holder was to minimize the prepulse voltage across the diode. The typical electron beam parameter was 180 kV, 26 kA, 100 ns, with a few hundreds of ampere per square centimeter current density. It was found that corrugated Perspex of length ges35 mm can eliminate the prepulse voltage but affects the rise time of the diode voltage. The diode voltage and current waveforms were analyzed with the bipolar space-charge limited flow model. The anode and cathode plasma expansion velocities were calculated using the perveance data. The plasma expands at 5.1 cm/mus for 18-mm anode-cathode gap and the plasma velocity increases for larger gap. Inserting a dielectric at the cathode holder could be a very effective method to reduce prepulse voltage at the electron beam diode, but it increases the rise time of the diode voltage and reduces the effective electron beam pulsewidth. The prepulse voltage reduces significantly (les10%) when an inductance is added to the charging circuit of the Blumlein line.

Intense electron beam generation in a high power cylindrical diode with a bipolar pulse

Our previously reported results demonstrated that an intense gigawatt relativistic electron beam can be generated in a cylindrical diode in the presence of prepulse. This article reports intense electron beam generation in a cylindrical electron beam diode when subjected to a high voltage bipolar pulse. The experimental results are compared to the Langmuir–Blodgett law. The diode perveance in the positive voltage pulse linearly increases with time due to the increase in the emission area. It was found that the electron beam can be generated from the diode during the negative voltage pulse due to a very little gap closure during the positive voltage pulse.

Prepulse minimization in KALI-5000

A pulse power system (1 MV, 50 kA, and 100 ns) based on Marx generator and Blumlein pulse forming line has been built for generating high power microwaves. The Blumlein configuration poses a prepulse problem and hence the diode gap had to be increased to match the diode impedance to the Blumlein impedance during the main pulse. A simple method to eliminate prepulse voltage using a vacuum sparkgap and a resistor is given. Another fundamental approach of increasing the inductance of Marx generator to minimize the prepulse voltage is also presented. Experimental results for both of these configurations are given.

Generation of short duration high power microwave using KALI - 5000

A pulse power system (1 MV, 5 0kA, and 100 ns) based on dual polarity charged Marx generator and Blumlein pulse forming line (PFL) was built to generate high power microwaves. This paper describes the inherent prepulse present with the Blumlein configuration and the mitigation strategies adopted. Further, a qualitative attempt to verify the generation of high power microwave output on the system is presented.

Effect of cathode diameter on intense relativistic electron beam generation in the presence of prepulse

Intense gigawatt relativistic electron beam generation studies were carried out in the presence of prepulse. Electron beams were generated using planar and annular graphite cathodes of various diameters at a fixed 25mm anode-cathode gap. For the planar cathode, the beam parameters obtained are 340keV, 24kA, and 100ns at a 680A∕cm2 current density. With an annular cathode, 346keV, 10kA, and 100ns electron beam could be generated at a 3.4kA∕cm2 current density. The peak electric field in the diode varies from 58to138kV∕cm. A bipolar prepulse voltage has been recorded at the diode for both the cathodes. The amplitude of the negative prepulse voltage varies with the Marx generator voltage but the time duration remains same. The positive prepulse voltage varies both in amplitude and time duration with the Marx generator voltage. Some shot to shot variation in the diode voltage and current were recorded for the annular cathode due to the nonreproducibility of the prepulse generated plasma. It was found that the...