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Pulsed Power Conference, 2003. Digest of Technical Papers. PPC-2003. 14th IEEE International

Date 15-18 June 2003

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  • 14th IEEE International Pulsed Power Conference

    Page(s): i - 1445
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  • Influence of initial conditions on capillary discharge device Capex 2

    Page(s): 729 - 732 Vol.2
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    The first time we have used McPherson's XUV grazing incidence spectrograph for measurement of a soft X-ray emission from the capillary discharge device Capex 2 and this spectrum is presented. Recently we have started to study an influence of pre-pulse capillary current on the soft X-ray emission in the fast capillary discharge and the latest results are shown as well. It was found that a very short intense spike that had been measured by a PIN diode doesn't necessarily correspond to a laser pulse. View full abstract»

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  • Wire-array holder critical in high wire-number z-pinch implosions

    Page(s): 733 - 736 Vol.2
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    The quality of high wire-number z-pinch implosions on Z using a dynamic-hohlraum configuration is significantly affected by the method of holding the wires. The two arrangements discussed here have led to differences of a factor of 1.6/spl plusmn/0.2 in radial x-ray power, where the higher power is produced by the holder with the superior current contact at the cathode. In support of this observation, single exploding wire data taken on a 250-ns pulser indicate that improved wire-electrode contact at the cathode permits greater energy delivery to the wire prior to current shunting to surrounding wire-plasma corona. View full abstract»

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  • Paraxial diodes on RITS-3

    Page(s): 737 - 740 Vol.2
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    The paraxial diode is the workhorse X-ray source at AWE for flash radiography of hydrodynamic experiments. It uses a gas filled cone to focus a 30-40 kA, 5 to 10 MV electron beam onto a tantalum target to produce a source 5-7 mm across. Future plans for a new hydrodynamics facility at AWE call for this diode to be fielded at a higher voltage on an inductive voltage adder (IVA) machine. The current machines at AWE are based upon single pulse forming line (SPFL) technology. To gain some experience with IVA technology and paraxial diodes, a series of shots were fired on RITS-3 at Sandia National Labs. Over 30 shots were fired on RITS-3 to optimise and investigate aspects of paraxial diode operation. The main concern with using RITS-3 was the excess current (/spl sim/110 kA) that would be dumped into the vacuum envelope and whether it would effect diode performance. The results that were obtained showed that this was not the case. On RITS-3 a best performance of 57R@1 m from a 5.7 mm spot was recorded, very similar to performance seen on comparable X-ray machines at AWE. View full abstract»

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  • Study of electric explosion of metal wires

    Page(s): 741 - 743 Vol.2
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    This paper is devoted to electric explosion of metal wires. A two-dimensional magnetohydrodynamic model based on the particle-in-cell method is used to consider the formation of strata and low-density plasma corona surrounding a wire. The stratoformation is shown to be due to evolving overheat instabilities. View full abstract»

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  • LSP simulations of the paraxial diode and comparisons with experimental data

    Page(s): 744 - 747 Vol.2
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    The standard paraxial diode is used extensively at AWE to field of variety of hydrodynamic experiments. This diode will also be used in the short term on IVA machines currently being developed for use in the forthcoming HRF. The short term goal for the HRF is to produce 600 R @ 1 m in a 5 mm spot on a 14 MVolt IVA machine. In support of this HRF proposal 2-D PIC simulations using the code LSP have been undertaken to understand the physics of electron beam propagation in the diode. Currently the code is being benchmarked against experimental data from two machines: E-minor and Mogul-E. Some preliminary comparisons will be made in terms of X-ray dose and radiographic spot size. Another important benchmarking parameter is the net current has an important effect upon the behavior of the electron beam. The beam electrons oscillate about the beam axis according to the betatron wavelength with the first focal point of the beam dependent upon the net current established within the gas cell. In this paper we discuss LSP predictions for diodes fielded at voltages up to 10 MV and compare findings with currently available experimental data. View full abstract»

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  • Explosion of thin aluminum foils in air

    Page(s): 748 - 751 Vol.2
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    The electrical explosion of a cylindrical Al foil was studied. The experiments were carried out using an inductive storage facility with a current of up to 40 kA. Owing to the high inductance of the storage (240 /spl mu/H), the current was staying constant during the explosion process. The fuse explosion was studied in the time range of 0.1 ms View full abstract»

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  • Experimental study and development of a single focus burst X-ray flash

    Page(s): 752 - 755 Vol.2
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    A compact single focus X-rays flash device is described in this paper. This device is composed of the following essential components: a 50 kV high voltage power supply, a capacitor bank, a pulse forming line, a high frequency and high voltage switch, a voltage multiplier and an X-ray tube. Before breakdown into the X-ray tube, voltage can be rise up to 400 kV, leading to photon of maximum energy around 400 keV. The duration of voltage pulses is 100 ns. The device can work in two different modes: pulsed mode up to 700 Hz; or in the burst mode at very high frequency. The number of shots in a burst can be chosen between 2 and 6. In burst mode, the system can work up to 20 kHz. View full abstract»

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  • Radiographic performance of Cygnus 1 and the Febetron 705

    Page(s): 756 - 759 Vol.2
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    Spot sizes are measured for medium energy X-ray generators. The Cygnus X-ray source [J. R. Smith et al., 2002] is developed for support of the Sub-Critical Experiments Program at the Nevada Test Site. Cygnus uses proven pulsed power technology to drive a rod pinch diode at 2.25 megavolts. Four rads at one meter is achieved in a 50-ns FWHM pulse and the radiographic spot size is as small as 1 mm-diameter. Radiographic spot size is measured employing roll bars and resolution targets. Images are recorded on film and storage phosphor, digitized, and analyzed. The Febetron 705 X-ray source operates at 2.3 megavolts and is rated at 500 millirads at one meter. A demountable diode tube provides the ability to replace the standard diode with custom hardware. Spot sizes for standard hardware are measured. New diode designs are investigated in an effort to generate smaller radiographic spot sizes to produce improved radiographic images. View full abstract»

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  • Computational method for the dispersion relation of a pulsed Cerenkov free electron maser system

    Page(s): 763 - 766 Vol.2
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    We have constructed a Cerenkov maser oscillator designed to operate at 16.9 GHz with a solid electron beam accelerated to 70 kV, using an alumina tube, fitted into a copper pipe. The measurements of the dispersion curves for such a cavity of various dielectrically loaded structures are presented. A method for calculating efficiently the dispersion curve of a cylindrical Cerenkov free electron device having a small gap between the dielectric liner and the waveguide wall is also described. In any practical realisation, such a gap cannot be avoided and the results obtained here indicate that the dispersion curve can be very sensitive to its thickness. View full abstract»

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  • Cooling system transient analysis using an electric circuit program analog

    Page(s): 767 - 770 Vol.2
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    By exploiting the common mathematical similarities between electrical and thermal circuits, an electric circuit transient analysis program may be used to analyze the transient behavior of thermal circuits. This is an especially convenient approach for the analysis and optimization of the cooling performance of burst mode type electrical apparatus such as high power transmitters. The relations between electrical components and the equivalent thermal components are established such that given the thermal component characteristics, one may then write and electric circuit with the proper values and then run the model to determine the performance in electrical parameters that are then easily interpreted as thermal parameters. Similar techniques have been used for the thermal analysis of components such as semiconductor devices [A. R. Hefner and D. L. Blackburn, Thermal Component Models for Electro-Thermal Network Simulation] and analog hardware [X. Huang and H. A. Mantooth, June 2000]. In this paper the P-Spice/spl trade/ program is used as an example; however, the same procedures may be implemented using any electric circuit analysis program. View full abstract»

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  • A two dimensional electromagnetic-electroplastic modelling technique

    Page(s): 771 - 774 Vol.2
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    The use of two dimensional filamentary modelling techniques has proven to be an accurate approach to modelling the complex electro-magnetic interactions that occur in high magnetic field generation experiments. Due however to the nature of this modelling, limitations arise when considering two dimensional, and three dimensional deformation of the geometry. Accurate modelling leads to a fundamental understanding, and consequently enables the generation system to be optimised. This paper outlines the preliminary steps in investigating into the potential and suitability of finite element analysis for the modelling of two high magnetic field generation experiments; single-turn coil technique, and /spl theta/-pinch flux compression, using a commercially available software package, ANSYS. View full abstract»

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  • Investigation of Z-pinch instability development in the non-ideal MHD regime

    Page(s): 775 - 778 Vol.2
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    The linearized Hall fluid model is used to study the m = 0 sausage and m = 1 kink instabilities in Z-pinch plasmas. A general set of equations that permits the evaluation of axial and azimuthal sheared flow and an axial magnetic field has been employed. The problem is then treated numerically by following the linear development in time of an initial perturbation to the equilibrium state of the plasma. Our results indicate that non-ideal magnetohydrodynamic (MHD) phenomena are important in the analysis of these instabilities. This is illustrated by including the Hall term in the analysis of the m = 0 and m = 1 instabilities in the presence of an axial magnetic field. It is also shown that numerical results are very sensitive to the boundary conditions and initial equilibrium profiles. Methods for reducing numerical inaccuracies in the solutions for growth rates are also discussed. View full abstract»

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  • Monte Carlo optimization multi-pass Bremsstrahlung target for pulsed X-ray source

    Page(s): 779 - 782 Vol.2
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    One of optional version of multi-pass Bremsstrahlung target for intensive pulsed X-ray source is described. Monte Carlo 3-d simulation of Bremsstrahlung characteristics of multi-pass target is discussed. The target under consideration is thin tantalum foil embedded in uniform magnetic field whose direction is oblique to the foil normal, but in contrast to [J. A. Halbleib Sr., 1974] the target is oriented such way that magnetic field direction is parallel to beam axis. X-ray target efficiency is calculated depending on magnetic field, thickness, inclination, electron energy and injected electron angle distribution. View full abstract»

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  • Properties of relatively-dilute plasmas in pulsed-power systems obtained from high-accuracy laser spectroscopy

    Page(s): 785 - 788 Vol.2
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    We describe a novel application of laser-spectroscopy to investigate the electric fields and the properties of relatively dilute plasmas under high-power pulses at the nanosecond time scale. The method is based on resonant laser-pumping combined with electron excitations and deexcitations by the plasma electrons, which allows for simultaneous observations of various line intensities (due to both allowed and forbidden transitions). These observations, together with novel line-shape calculations recently developed, allow for obtaining the electron density, electron temperature, and electric fields. Another feature of the method developed is that plasma-doping is incorporated, which, combined with the laser spectroscopy, yields 3D-spatially-resolved (sub-mm) measurements. The study is carried out in a coaxial-pulsed-plasma configuration (a plasma opening switch). For the first time, line-shape diagnostics was successfully applied to determine the properties of plasmas with densities down to 10/sup 13/ cm/sup -3 /at a sub-microsecond time scale. The electron density was determined rather accurately even though the line profiles were dominated by the instrumental and Doppler broadenings. Such diagnostics can be used for the investigation of high-current carrying plasmas formed in high-power transmission lines, plasma switches, ion and electron diodes, and plasma sources. View full abstract»

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  • Determination of the mass distribution in a gas puff by laser induced fluorescence

    Page(s): 789 - 792 Vol.2
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    Recently, experiments have shown that laser induced fluorescence (LIF) can be a useful diagnostic for determining the mass distribution from a gas puff system used in z-pinch plasma radiation sources [B. H. Failor et al., February 2003]. In this work we report on our efforts to develop a LIF system, using nitric oxide (NO) as the tracer, to determine the mass distribution in the gas puff nozzle assembly used in [B. H. Failor et al., February 2003]. The same assembly has also been extensively studied at NRL using laser interferometry [Y. Song et al, 2000]. Preliminary results indicate that the NO-LIF, laser interferometry and the previous LIF results agree to within 20%. Concentrations of NO less than 0.1% can be used. View full abstract»

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  • Measurements of the radiated fields and conducted current leakage from the pulsed power systems in the national ignition facility at LLNL

    Page(s): 793 - 796 Vol.2
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    An important pulsed power system consideration is that they inherently generate fields and currents that can cause interference in other subsystems and diagnostics. Good pulsed power design, grounding and isolation practices can help mitigate these unwanted signals. During the laser commissioning shots for the NIF Early Light milestone at LLNL, measurements were made of the radiated field and conducted currents caused by the power conditioning system (PCS) modules with flash lamp load and the plasma electrode pockels cell (PEPC) driver. The measurements were made in the capacitor bay, laser bay, control room and target bay. The field measurements were made with B-dot and E-dot probes with bandwidth of about 100 MHz. The current measurements were made with a clamp on probe with a bandwidth of about 20 MHz. The results of these measurements show fields and currents in the NIF Facility well below that required for interference with other subsystems. Currents on the target chamber from the pulsed power systems are well below the background noise currents. View full abstract»

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  • Characteristics of capillary discharge Ne-like Ar soft X-ray laser

    Page(s): 799 - 802 Vol.2
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    Soft X-ray laser has some convenient properties such as short wavelength, monochromaticity and coherency. Aiming at the development of a table-top size laser, we have designed, fabricated and tested a soft X-ray device, which uses a capillary discharge to achieve neon-like argon lasing (J = 0 - 1, /spl lambda/ = 46.9 nm). The pulsed power generator consists of a Marx generator, a pulse transformer, a pulse forming line, a gap switch and a capillary made of Al/sub 2/O/sub 3/ ceramics. Previously, spike output has been observed, when operating the device with a predischarge current of 5 to 15 A and a main discharge current of 9 to 35 kA with a rise time of 55 ns in an argon gas pressure range from 100 to 800 mTorr. When the distance between the end of capillary and the X-ray diode detector changed, the amplitude of spike signal does not change. This indicates that the spike signal shows directivity, which is a property of the laser. In the present study, spectroscopic measurement has been conducted using a grazing incidence spectrometer. The line at 46.9 nm has been observed. The X-ray diode measurement has also been conducted by varying the capillary length,. The result shows that the laser output exponentially increases with increasing the capillary length. View full abstract»

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  • New residual stress mapping tool applied to Atlas current joint design

    Page(s): 805 - 808 Vol.2
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    A redesigned cylindrical liner system has been implemented for use on the Atlas capacitor bank. This new design dramatically changes how the liner, glide planes and current joints of the system are formed. The previous design relied on interference of the liner with the glide plane by thermal shrink fit using liquid nitrogen coolant to form current joints. The new design achieves the required fit by mechanically distorting soft metals with a swaged joint. In this paper, we present the results of the first application of a new residual stress mapping technique, the contour method, to the design and fabrication process of the Atlas upper current joint. One of the strengths of the contour method is that it provides a full cross-sectional map of the residual-stress component normal to the cross section. The results showed significant stresses in the stainless steel glide plane with expected maximum compression near the joint and stresses in the aluminum part liner and return current conductor that corresponds well with measured form distortions. View full abstract»

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  • Examination of liner stability during magnetic implosion using experiments and simulations

    Page(s): 809 - 812 Vol.2
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    Los Alamos has been conducting a number experiments to examine dynamic properties of materials using high-energy pulse power generator systems. These experiments are conducted in a Z-pinch configuration typically with an outer aluminum liner to carry the current, develop the acting force, and act as the driving element. The peak magnetic fields produced by these systems have ranged from 0.5 to 1.7 mega gauss. The onset of what has been called Magneto-Raleigh-Taylor (MRT) instabilities in the outer aluminum liner, when excessive current is applied, has been considered a limitation on the design of these liners. However, in several cases where the material of the liner was calculated to be completely melted the outside liner surface remained stable. Analysis of the data from this and several other experiments and comparison to 1D MHD simulations has already permitted us to examine how the drive conditions on this aluminum layer appear to effect the likelihood of onset of these instabilities. Additionally, careful variations of drive conditions, initial liner surface conditions, and EOS properties (including conductivity) suggest two phenomenons that appear to cause onset of instability. First, while the nature of the instability may still be fundamentally driven by the acceleration of a fluid interface, the effect may be drastically accentuated by the onset of liquid to vapor phase change if the material is allowed to approach too closely to the saturated liquid line. Furthermore, several observed cases which remained stable even after melting suggest that there may be drive conditions which maintain the aluminum at densities and temperatures above the saturated liquid line and significantly delay the onset of MRT instabilities. Second, the gradient of distribution of forces within the melted liner may also impact the growth of instabilities. We will also present the results of 2D simulations of these conditions and examine in greater detail the apparent mechanisms b- which these instabilities grow. View full abstract»

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  • Short circuit protection of high speed, high power IGBT modules

    Page(s): 815 - 818 Vol.2
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    At SLAC, research and development for the next linear collider (NLC) is progressing. The 8-Pack project is a test stand in which key NLC components will be developed. Presently the setup is such that an induction modulator [R. L. Cassel et al., The Prototype Solid State Induction Modulator for SLAC NLC] will generate 400 kV, 1200 A, and 1.6 /spl mu/s flattop pulse to drive four XL4 X-band klystrons. This requires the use of 76 high power IGBT modules operating in parallel at 3600 A and up to 2200 V each. IGBT switching speeds and short circuit protection from klystron arcs are major concerns. This paper describes a gate drive circuit with a new method to protect IGBT modules under short circuit conditions. Using a dI/dt control technique, the gate drive circuit enabled the Mitsubishi module CM600HB-90H to switch 4000 A at speeds up to 10 kA//spl mu/s in normal operation, while holding the short circuit peak-current to about 8000 A. Results from the single IGBT test and the 8-Pack Modulator prototype will be presented. View full abstract»

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  • Semiconductor modeling for multi-layer, high field, photo-switch using sub-bandgap photons

    Page(s): 819 - 822 Vol.2
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    High electric field geometries for high power, photo-conductive switches made possible by employing sub-bandgap photons and inter-bandgap dopants / defects are being investigated for compact pulse power systems. The high field, long absorption depth package reduces the required linear mode, optical closure energy and also reduces the conduction current density through the active material and at the contacts. In addition, the long absorption depth package increases the area available for thermal management and in concert with the reduced current density should increase the lifetime of the switch. This paper describes the semiconductor physics modeling of a multi-layer stack of GaAs wafers in a high electric field configuration. The model results of heavily doped n+ regions on electron injection, leakage current, and voltage hold off is discussed In addition, the modeling of the transverse injection of optical closure energy is discussed. View full abstract»

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  • Opportunities for employing silicon carbide in high power photo-switches

    Page(s): 823 - 826 Vol.2
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    High electric field geometries for high power, photoconductive switches made possible by employing subbandgap energy photons and inter-bandgap dopants / defects are being investigated for compact pulse power systems. The high field, long absorption depth package reduces the required linear mode, optical closure energy and also reduces the conduction current density through the active material and at the contacts. This paper describes the opportunities for employing semi-insulating SiC wafer in the University of Missouri-Columbia, high electric field configuration. The parameters of semi-insulating SiC materials and methods of fabricating such materials into a high power photo-switch are discussed. In addition, transient modeling of the transverse injection of optical closure energy is discussed. View full abstract»

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  • Surface flashover characteristics of semiconductor

    Page(s): 827 - 830 Vol.2
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    Two kinds of silicon samples with distinct surface treatment, i.e., one surface was chemically etched and the other was unetched, were used to investigate the flashover characteristics of semiconductor under impulse voltage in vacuum. Before flashover, the ohmic current was observed for unetched samples and the space charge limited (SCL) current for etched samples, respectively. Meanwhile both samples showed quite different flashover tracks. It was believed that all the phenomena were due to their different density and distribution of surface states. A new model was proposed to describe the development process of surface flashover along semiconductor, i.e., the thermal effect and subsequently the current filament with the applied voltage. It was suggested that the flashover phenomena occurred in the interface layer of silicon butted to electrodes and in its lateral layer near to the ambient. View full abstract»

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  • Control over plasma distribution on explosive emission cathodes

    Page(s): 833 - 836 Vol.2
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    Distributions of emission centers (ECs) on planar explosive emission dielectric (velvet) cathodes at moderate electric fields of 30-70 kV/cm and pulse durations of /spl sim/2 /spl mu/s with the use of a fast framing camera have been investigated. The experimental results suggest a link between the ECs distribution and current conduction paths through which the electron current is supplied to the cathode plasma. On bare velvets, the surrounding metal electrode was shown not to be of primary importance for the current conduction, instead, the current is supplied to explosive emission plasma mainly through the base of the velvet fabric. A development of a circle of brighter and larger ECs along the perimeter of the cathode was normally observed shortly after the beginning of the high voltage pulse. These ECs were found to be a major factor in the diode perveance growth and instability. Domination of the ECs on the cathode periphery has been suppressed by adding a pattern of well-defined current conduction points, e.g. perforations of the velvet fabric, to the cathode design. View full abstract»

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