Pulsed Power Conditions Research Articles

Modeling of an induction plasma under transient turbulent flow conditions

A renormalization group (RNG) k-ε turbulence model was employed to investigate the role of turbulence for the transient behavior of the radio frequency induction plasma discharge. Time-dependent conservation equations for the plasma and turbulence under local thermal equilibrium (LTE) conditions were solved numerically in two-dimensional, axisymmetric coordinates. Responses of energy, momentum, and turbulence to steplike and pulsed power changes in an Ar-H2 plasma with a hydrogen volume concentration of 10.9%, and a total gas flow rate of 104.0 slpm were studied. The corresponding Reynolds number at the inlet of the discharge cavity was 2667. The turbulence model was validated qualitatively by comparing the predicted results with experimental observations under pulsed power conditions. It is found the transient behavior of the plasma energy and momentum are mainly governed by radial convection, while that of the turbulence is primarily determined by axial convection. These gave rise to a 5–10 ms delay in the response of the turbulence lagging behind the temperature field, for sudden power changes, under current operating conditions. A comparison between the results predicted using the RNG k-ε turbulence model and those obtained using the laminar model indicates the presence of turbulence leads to a longer relaxation time of plasma. Under pulsed power conditions, the plasma temperature responds to power changes almost instantaneously, and it is always in a transient state. In contrast, variation in the relative turbulent viscosity is insignificant and it is concluded that the turbulence is in a quasisteady state when the period of a pulse is between 10 and 15 ms. By comparing the predicted results with images obtained using a high-speed camera (0.67 ms/frame) under the same operating conditions, we found that the turbulence model predicted a more accurate transient behavior in terms of plasma volume and temperature than the laminar model does.

Overstressing of High-Voltage Capacitors

In compact pulsed power conditioning systems, a high electric energy density of its capacitors is of interest. Commercially available capacitors are normally designed for long storage time and long lifetime. The performance of capacitors in terms of energy density capability can be improved by overstress or overcharge, that is, charging to a significantly higher energy density than specified. This paper explores the limits of overstressing commercially available capacitors for short time spans. The selected capacitors have a nominal dc voltage in the range of 2.5-10 kV and a capacitance in the range of 0.015-0.12 /spl mu/F. Two different storage times have been considered: 2 /spl mu/s and 20 ms. A high-voltage test setup was constructed. For the short storage time, it was possible to overstress the energy density as compared to nominal values with a factor of 26 and for the long storage time with a factor of 14 for the best performing capacitor. Other capacitors behaved significantly poorer, especially for the long storage time.

Effects of magnetic field on the carrier density distribution of semiconductor power device operated in pulsed power conditions

AbstractTurn‐on characteristics of semiconductor power devices are evaluated under external magnetic field to study the effects of external magnetic field generated in a pulsed power circuit. Two pin diodes that have a basic structure of power devices are connected in parallel and driven by a pulsed voltage source. It was found the magnetic field applied to one diode in the perpendicular direction of current‐flow changed the current balance between the diodes. Besides the on‐resistance of a diode was increased under external magnetic field. The carrier‐density distribution inside of the diodes was measured by using a free carrier absorption method. The data show that the carrier‐density distribution changes from nearly the uniform one to the one‐sided one. It can be concluded that the effects of magnetic‐field have to be considered for the evaluation of switching characteristic in pulsed power operations. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(1): 10–16, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10271

Generation Technologies of High Repetition Rate Pulsed Power.

Recently, high repetition rate, long lifetime, and high reliability pulsed power generators have been developed using semiconductor switches. We have studied and developed an all solid-state pulsed power generator for industrial applications such as a high repetition rate pulsed gas laser and a pulsed ozonizer. Recently, semiconductor power device technology has improved the performance of fast high-power switching devices. However, the semiconductor switch is still not sufficient to drive the pulse laser and the pulse ozonizer directly. Therefore, the semiconductor switch can be used in practical application with the assistance of a magnetic switch and a gate driving technique. This all solid-state generator consists of a semiconductor switch and a magnetic switch. The progress of high repetition rate pulsed power generators is reviewed herein, with particular emphasis on pulse power conditioning by solid-state switching techniques.

X-ray photoelectron spectroscopy investigation and characterisation of plasma polymerised isocyanatoethyl methacrylate

Various polymeric and non-polymeric samples were modified by means of plasma polymerisation of isocyanatoethyl methacrylate (IEM) vapour in mixture with argon. The aim of the work was to find the best experimental conditions and compare the down-stream plasma polymerisation and pulsed plasma polymerisation techniques. The IEM was chosen for superior reactivity of its isocyanato group (–N=C=O), predominantly towards amino terminated compounds. A tubular reactor with the external radio frequency (27.12 MHz) excitation was used. Surface modification was performed at various distances from the plasma zone (from 0 to 50 cm) in down-stream set-up and at different duty cycles (from continuous wave to 1:20 m s) in pulsed reactor set-up. Modified surfaces were investigated in detail by means of X-ray photoelectron spectroscopy. The best correlation among the IEM reference and plasma polymerised IEM was obtained for 20–30 cm distance under the down-stream conditions and at 1:20 m s for the pulsed power conditions, giving a comprehensive picture of those two plasma deposition technique.

Experimental and analytical investigation of a pulsed power conditioning system for magnetic flux compression generators

The pulsed power conditioning system (PPCS) is one of the key enabling technologies for using the energy output of a magnetic flux compression generator (MFCG). This paper shows the results of comprehensive experimental studies of an inductive energy storage system using an exploding wire fuse. The effects of metal oxide varistors (MOVs) for use as pulse-shaping devices are also presented. The experimental results are complemented by a comprehensive evaluation and interpretation of the results using the tools available in the professional version of MathCAD.

EML technology research in China

In the last 20 years, electromagnetic launch (EML) technology has been developed in the US and Europe, and the electromagnetic (EM) launcher has been regarded as a prospective equipment of propulsion. In the early 1980s, experiments on EML technology were done in some Chinese laboratories, and a lot of work has been finished in order to systematize the theory of EML technology in some universities and institutes. One result is that the Chinese book 'Principles of Electric Guns' was one of the first publications of its kind in the world. Now, there are seven organizations which are participating in the research or experiments in China. They are the Southwest Institute of Fluid Physics (SWIFP), the Institute of Plasma Physics (IPP) of the Chinese Academy of Sciences, Nanjing University of Science and Technology (NUST), Huazhong University of Science and Technology (HUST), Ordnance Engineering College (OEC), Xidian University (XU) and Institute 208 of Chinese Ordnance Industry (I208COI). The invention patents relating to the EML technology have been applied for; three books which directly relate to the EML technology have been published; some papers have been translated, compiled and published internally. The 15 papers submitted to this symposium involve the rail gun, the coil gun, the electrothermal-chemical (ETC) gun, pulsed power conditioning, energy storage, and an overview.

Kinetics of DC Discharge Plasma Polymerization of Hexamethyldisiloxane and Pyrrole

This paper investigates DC plasma polymerization kinetics by combining plasma parameters with film deposition rate in different conditions. The monomers hexamethyldisiloxane (HMDSO) and pyrrole were used. Both single and double Langmuir probes were used to measure the plasma parameters in pulsed power and continuous discharges. In order to avoid probe tip contamination, the probe was heated. Plasma density and electron temperature are reported. The electron current wave form is obtained in pulse power conditions. From the data, a plasma polymerization model is proposed. The conclusion is that the monomer molecules and free radicals adsorbed on the substrate surface react with activated sites produced by high energy ions bombarding the film, resulting in polymerization at the film surface.

High-energy pulsed-power conditioning and switching for flux-compression generators

Devices based on the flux-compression process provide extremely effective and inexpensive alternatives to the capacitor bank as a means of generating high-current and high-energy pulses. The energy is however released at too slow a rate for many applications and, when a fast-rising current is to be driven through a high-impedance load, one or more stages of pulse sharpening are necessary between the compressor and the load. After examining the concepts that are involved in the magnetic energy transfer process, this article describes typical opening and closing switches for use in each stage of the conditioning.

A 1 kHz repetition-rate 500 W CO2 TEA laser employing solid-state pulse power conditioning

The long-term operation of a 1 kHz, 500 W transversely excited atmospheric CO2 laser has been realized by using an all-solid-state exciter. The laser system consisted of a fast-gas-flow tunnel containing a discharge head, a pulsed power supply made of an all-solid-state exciter, and a gas regenerator with a gas analyser. The energy transfer efficiency of the exciter was 65% and an overall laser efficiency of 5.2% was obtained. Continuous operation of more than 107 shots has been achieved for sealed-off conditions.

High-Power TEA CO2 Lasers.

Progress of high-power TEA CO2 lasers is reviewed with paticular emphasis on pulse power conditioning by solid-state switching techniques. The use of the solid-state switches is a key technology forhigh-power, long-life operation because the life time of a discharge switch becomes a limiting factor of the operation life of such lasers. Another limiting factor is the degradation of the laser gas mixture. In this review, we summarize the present status of high power TEA CO2 lasers and then discuss on technical problems to be overcome for the development of high-repetition-rated TEA CO2 lasers. We also introduce two types TEA CO2 laser employing a solidstate exciter which is newly desinged and constructed for the demonstration of long-life and high-power operation.

Using a small hybrid pulse power transformer unit as component of a high-current opening switch for a railgun

The hybrid pulse power transformer (HPPT) is a unique concept utilizing the ultrafast superconducting-to-normal transition process of a superconductor. When used in the form of a hybrid transformer current-zero switch (HTCS), this creates an approach in which the large, high-power, high-current opening switch in a conventional railgun system can be eliminated. This represents an innovative application of superconductivity to pulsed power conditioning required for the Strategic Defense Initiative (SDI). The authors explain the working principles of a 100-kJ unit capable of switching up to 500 kA at a frequency of 0.5 Hz and with a system efficiency of greater than 90%. Circuit analysis using a computer code called SPICE PLUS was used to verify the HTCS concept. This concept can be scaled up to applications in the several mega-ampere levels.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Compact pulsed transformer power conditioning system for generating high voltage, high energy, rapid risetime pulses

Compact, lightweight air-core pulse transformers in open air have been developed. A SHIVA Star capacitor bank module (36 mu F, 120 kV, 260 kJ) was used to drive a transformer for generating high-voltage pulses into resistive loads. Voltages reaching 400 kV were delivered to a 6 Omega load at a total energy delivery of 60 kJ to the load. In order to achieve single high energy pulses to the load, several fused primary concepts were investigated and developed. These concepts along with transformer construction and first-order models of the system are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Lightweight magnet for space applications

The use of cryogenic and superconducting magnets in space is being investigated for pulsed power generation, power conditioning and energy storage and could play a major role in the Strategic Defense Initative (SDI) program. Potential space magnet applications, current technological limits and areas where additional development is required have been identified. A short history of superconducting magnets in space is included. Technology study results, including consideration of zero-gravity conditions for magnet cooling, space-based refrigerator/liquefiers, advanced composites to reduce magnet weight and structures that satisfy launch and space environmental requirements are presented. Computer programs have been developed to optimize spaceborne magnet system weight with respect to the power supply, magnet operating current density, cooling scenario, charge and discharge rates, load characteristics and magnet configuration. Ground-based magnets built to date have stored energy to mass ratios (specific energies) of less than 3 J/gm ; it is expected that space-based magnets with specific energies of more than 50 J/gm can be designed and built in the near future.

An approach to the heat flow problems and transient temperature rise in nonlinear semiconductor media

The heat flow equation in Liebman's (implicit) formulation is solved for nonlinear semiconductor media under pulsed power conditions. The temperature rise was computed for nonlinear, temperature-dependent properties of the materials, using Richtmeyer's algorithm. The method and the results of computations are useful in extension of the nonlinear heat flow theory to semiconductor media.

Transient temperature rise in silicon semiconductor devices

The temperature rise in silicon devices under pulsed power conditions is calculated by a numerical method which takes into account the nonlinear properties of the materials. Power is assumed to be dissipated in a thin but finite layer at the surface of a one-dimensional structure. The effect of various types of heat sinks on the peak temperature rise is shown.

Analysis and design considerations of microwave radial cavities for ultrasonic applications: Seguin, H.J. IEEE transactions on sonics and ultrasonics, SU-14, no. 2, p. 70 (1967)

Abstracf-The theoretical and practical aspects involved in the design of radial microwave cavities for ultrasonic applications are considered. A semigraphical approach to the solution of the trans- cendental resonance equation is developed along with a complete set of relations by which the performance and efficiency of the cavity design may be determined. Special application of this analysis is made in the design and construction of S band microwave ultra- sonic cavities for use in viscoelastic relaxation investigations in liquids at 3 GHz. N THE FIELD of microwave ultrmonics and laser communirations it is frequent,ly found t.hat radial microwave cavity resonat.ors provide a convenient, and efficient, means of exciting piezoelectric and electro- opt,ic materials. This paper is intended to present a treatment of the analysis and design considerations in- volved in the development of these radial cavities. The treatment developed here is presented primarily with a view towards the generation and detection of ultrasound for viscoelastic relaxat,ion studies;*') however, the basic cavit,y t,heory is quite general and should in principle be equally valid for elast.ooptic and electrooptic applications. The cavity adopted for analysis is of the symmet,ricttl double-reentrant configurative shown in Fig. 1. For the sake of clarity all tuning, coupling, and associated mech- anisms have been omitt,ed. A complete assembly drawing and description of the 3 GHz cavities construrted for viscoelastic studies is availahlc in the ljt,erat>ure. ('l Normally the material to be excited is placed in t,he gap region between the reentrant cavit.y electrodes. This material may be any of several low loss substances surh as ZnO, CdS, KDP, LiNboa, etc., depending on the :qplication. For the ultrnsonic application considered here the material was a single crystal disk of piezoelectric quartz, which was held in position by a teflon assembly as indicated in Fig. 1. The radial configuration was chosen for two basic reasons, t,hese being high filling factor and relative freedom from nonaxial elect,ric field components. These nonaxial fields can cause considerable trouble by generating un- wanted modes in t,he crystal. In order to provide flLsh over protect,ion under high pulsed power conditions and to insure that the excit.ed region was free of any edge mounting strains, the diameter

Analysis and Design Considerations of Microwave Radial Cavities for Ultrasonic Applications

Abstracf-The theoretical and practical aspects involved in the design of radial microwave cavities for ultrasonic applications are considered. A semigraphical approach to the solution of the trans- cendental resonance equation is developed along with a complete set of relations by which the performance and efficiency of the cavity design may be determined. Special application of this analysis is made in the design and construction of S band microwave ultra- sonic cavities for use in viscoelastic relaxation investigations in liquids at 3 GHz. N THE FIELD of microwave ultrmonics and laser communirations it is frequent,ly found t.hat radial microwave cavity resonat.ors provide a convenient, and efficient, means of exciting piezoelectric and electro- opt,ic materials. This paper is intended to present a treatment of the analysis and design considerations in- volved in the development of these radial cavities. The treatment developed here is presented primarily with a view towards the generation and detection of ultrasound for viscoelastic relaxat,ion studies;*') however, the basic cavit,y t,heory is quite general and should in principle be equally valid for elast.ooptic and electrooptic applications. The cavity adopted for analysis is of the symmet,ricttl double-reentrant configurative shown in Fig. 1. For the sake of clarity all tuning, coupling, and associated mech- anisms have been omitt,ed. A complete assembly drawing and description of the 3 GHz cavities construrted for viscoelastic studies is availahlc in the ljt,erat>ure. ('l Normally the material to be excited is placed in t,he gap region between the reentrant cavit.y electrodes. This material may be any of several low loss substances surh as ZnO, CdS, KDP, LiNboa, etc., depending on the :qplication. For the ultrnsonic application considered here the material was a single crystal disk of piezoelectric quartz, which was held in position by a teflon assembly as indicated in Fig. 1. The radial configuration was chosen for two basic reasons, t,hese being high filling factor and relative freedom from nonaxial elect,ric field components. These nonaxial fields can cause considerable trouble by generating un- wanted modes in t,he crystal. In order to provide flLsh over protect,ion under high pulsed power conditions and to insure that the excit.ed region was free of any edge mounting strains, the diameter

The Operation of Bolometers Under Pulsed Power Conditions

The dynamic behavior of Wollaston (thin platinum) wire bolometers under pulsed power conditions is examined and shown to be responsible for certain errors in the measurement of microwave power. These errors, in order of importance, arise from the nonlinearity of bridge null arm current as a function of bolometer resistance, from the nonlinear cooling of the bolometer in the interval between pulses, from the time variation of VSWR of the bolometer and from the time variation of bias power in the bolometer. The total error is found to be proportional to the bolometer resistance excursion during a pulse; the resistance excursion, in turn, is proportional to the pulse energy. All of these errors, with the exception of that due to nonlinear cooling, are amenable to calculation. The latter error was evaluated by subtracting the sum of the computed errors from the experimentally determined total error. The total error is about 14 to 15 per cent per 100 ohms resistance excursion for two widely used bolometer types under typical conditions. More than half of the above error may be eliminated by suitable design of the bridge circuitry.