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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 25 mm anode-cathode gap. For the planar cathode, the beam parameters obtained are 340 keV, 24 kA, and 100 ns at a 680 A/cm2 current density. With an annular cathode, 346 keV, 10 kA, and 100 ns electron beam could be generated at a 3.4 kA/cm2 current density. The peak electric field in the diode varies from 58 to 138 kV/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 effect of prepulse is more pronounced in the cathode of larger diameter. [ABSTRACT FROM AUTHOR]

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 typical electron beam parameter was 280 kV, 18 kA, 100 ns, with a few hundreds of A/cm2 current density. 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/μs 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 diode closes at a faster rate in the presence of nylon sheet on anode. Nylon materials are released into the diode region due to the electron beam bombardment and get deposited on the cathode. This deposition affects the subsequent electron beam generation. [ABSTRACT FROM AUTHOR]

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 ≤1.65 cm 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 5 cm/μs for 1.85 cm 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 ≤1.85 cm. [ABSTRACT FROM AUTHOR]

Intense relativistic electron beam diode has been operated without a prepulse switch. Our previously reported results demonstrated that the large pulse power systems in the presence of prepulse can deliver gigawatt power pulses into a matched load if the anode cathode gap is set larger than that estimated by the Child Langmuir relation. This article reports some more experimental results on the current and voltage characteristics, the shot to shot reproducibility of the diode in the presence of prepulse. Intense electron beam diode behavior was studied for various anode cathode gaps and voltages in presence of prepulse. It has been observed that for small gap, prepulse generated plasma completely fills the anode cathode gap and the diode behaves as plasma filled diode. At a large gap the beam parameters obtained are 420 keV, 22 kA, 100 ns. From the experimentally obtained values of perveance an upper limit was set up for the Marx voltage (or anode cathode voltage) and lower limit for the anode cathode gap in order to avoid the gap closure problem and the diode can be operated with a better shot to shot reproducibility. [ABSTRACT FROM AUTHOR]

Large pulse power systems in the presence of prepulse can deliver gigawatt power pulses into a matched load. While employing these pulse power systems for the generation of intense relativistic electron beams (IREBs), the prepulse initiated plasma closes the anode cathode gap, if the gap distance is set by the Child-Langmuir formula. In order to reduce the prepulse effect, the anode cathode gap has been increased for the generation of IREB with output parameters of 400 kV, 20 kA, and 100 ns pulse duration. In this paper the generation of IREB in the presence of prepulse without using any prepulse switch has been discussed. [ABSTRACT FROM AUTHOR]

Thick silicon dioxide (SiO2) films up to 5 μm have been deposited by helicon activated reactive evaporation (plasma assisted deposition with electron beam evaporation source) as both bilayer and trilayer structures, and the film stress was investigated in the context of optical waveguide fabrication. A model for stress in the SiO2–Si bilayer as a function of film thickness is formulated and interpreted in terms of Volmer–Weber film growth mechanisms. We find that island coalescence begins at a film thickness of less than 165 nm and continues until about 700 nm. Above approximately 1 μm thickness, the film continues growth as a continuous film. The stress in a deposited SiO2 film in an SiO2–Si–SiO2 trilayer structure was investigated by adapting the established Stoney’s equation for a trilayer system, and comparing it with a thermally grown SiO2 trilayer. A constant value of stress is obtained for the deposited SiO2 film for film thickness >1 μm which was consistently less than both measured and previously reported values of stress in thermally grown SiO2. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper presents a new high voltage pulse shaping methodology for pulsed power applications. The aim is to generate high voltage square pulse across anode cathode gap of e-beam diodes. The non-linear time varying perveance characteristics of e-beam diodes are used for shaping of output voltage pulse across it, generated directly from Marx generator. Analytically, it has been shown in the paper that under certain conditions, if achieved, Marx generator feeding an e-beam diode can produce a square-like pulse at the output, without any extra pulse shaping arrangements. Experimental results to support the analysis are also presented in the paper. [ABSTRACT FROM AUTHOR]