Micro-plasma jet improves triggering in pulsed power technology

Systematic studies have been carried out on the industrial applications of pulsed power at Extreme Energy-Density Research Institute (EDI), Nagaoka University of Technology, Nagaoka, with good collaboration with government, municipality and private companies. In particular, applications are emphasized to materials science by pulsed ion beam evaporation technique using high-density ion-beam-ablation plasma. Various kinds of thin films or ultrafine nanosized powders have been prepared very efficiently. Ultrafine nanosize powders can be successfully synthesized by pulsed wire discharge as well. Furthermore, fullerenes and carbon nanotubes have been prepared by pulsed wire discharge of a bundle of carbon fibers. Industrial applications have also been succeeded in the flue gas treatment of pulsed power for NOx and SOx gas treatment by pulsed corona discharge or relativistic electron beam. Pulsed microwaves have been obtained by virtual cathode oscillator scheme. Foil acceleration has been achieved by the reaction of the ablation plasma up to 8 km/s. For the industrial applications, high repetition rate pulsed power supplies have been developed by semiconductor switches such as MOSFET, IGBT, or static induction thyristor. (4 pages)

Recently, all solid-state pulsed power modulators, which are operated with high repetition rate, long lifetime and high reliability, have been developed to be used for industrial applications of plasmas, such as high repetition rate pulsed gas lasers, high energy density plasma (EUV sources) and pulse ozonizer. We have studied and developed high repetition rate compact pulsed power modulator for discharge plasma in water. This modulator is consisted of thyristor switch and magnetic pulse compression (MPC) circuits. This modulator is able to generate an output voltage of about 25 kV with voltage rise time of less than 200 ns. A repetition rate is 500 pulses per second (pps). We conducted the operation test and generated the streamer kind discharges in the water. We observed that plasma behavior is changed at high repetition rate of 500 pps.

Virtually all practical applications for intense ion beams require that the beam pulses be generated at high repetition rates. This paper reports the development of the first high pulse rate, long-lived ion beam diode. It is a magnetically insulated diode which has produced ∼75 keV proton and carbon beam pulses of 1.0–2.5 A/cm2 and 100 ns duration at up to 90 Hz in four pulse bursts. It has also produced 125 keV, 5 A/cm2 Ar beams at a steady 1 pulse per 30 s for over 1000 pulses between failures in many runs. This diode employs a magnetically confined anode plasma ion source, and the high repetition rate pulsed power systems are based upon saturable magnetic switching.

Recently, pulsed power technologies, including pulsed electric fields (PEFs) and time-modulated plasmas, are starting to be applied actively in agriculture and food processing. In the applications, compact pulsed power generators with moderate peak power and repetitive operation are developed for controlling discharge plasmas and electric field distribution. These applications are mainly based on the biological effects of a spatially distributed electric field and the chemically active species in the plasma. The PEFs are caused by applying pulse voltage between the electrodes and contribute to form pores on the cell membrane or to change conformation of protein. When the applied voltage exceeds the discharge onset criterion, plasmas are generated through the avalanche process of electron accelerated with intense electric field in a gas or liquids medium. The plasmas produce chemically active species, UV radiation, an intense electric field in the vicinity of discharge channel and shock waves, which also have different biological effects. The agricultural applications of pulsed power can be categorized as two phases: pre-harvest and post-harvest phases. The pre-harvest phase consists of seed germination, seedling growth, plant growth and growth mode change from vegetative to reproductive. Pulsed power technologies are used to promotion of seed germination, plant growth enhancement through direct stimulation or indirect effect such as inactivation of bacteria in soil and liquid hydroponic media, and promotion of mushroom fruit body formation. The post-harvest phase consists of harvesting the agricultural produce, storing the products, transporting the products to consumers and food processing such as drying, pasteurization (sterilization of bacteria), permeabilization and fermentation. The pulsed power technologies are also used to keep freshness of agricultural produce through decontaminating airborne, inactivating bacteria and decomposition of plant hormone in the storage containers. The poration of cell membrane by PEF contributes improvement of extraction of juice, nutritional agents, and antioxidant metabolites such as polyphenols from agricultural products. In this review, at first, a basis of pulsed power system for agricultural applications and bio-effect by high-electric field exposure is outlined. After that, pre-harvest and post-harvest agricultural applications are described. The utilization of pulsed power technologies to contribute efficient food processing and improve food safety and quality is also described.

This paper describes a new recycling method for metal-coated plastics. Pulsed power technology was used to remove a metal layer (aluminum) from CD-ROM. The progress of removal and the state of discharge were investigated in detail. In addition, the shadow picture method including a digital image processing was used to estimate removal amount. A pulsed power generator using magnetic pulse compression (MPC-PPG) with maximum storage energy of 40 J/pulse was used. Pulsed power was applied to concentric ring electrodes placed on the CD-ROM. Separation between electrodes was about 35 mm. Results show that almost all of the metal layer was removed under application of about 30 shots of pulse power. A strong correlation between the removed area measured by the shadow picture method and the removed mass was obtained, allowing the removed area and mass to be measured instantly by the shadow picture method. Furthermore, it was revealed that the discharge onset voltage increases with gap length between the electrodes and the aluminum layer left on the surface. Due to the surface flashover voltage between ring electrodes of about 80 kV, a pulsed power source output voltage larger than 80 kV is required.

Emission from ferroelectric cathodes

The discipline of pulsed power hydrodynamics is a new application of low-impedance, pulsed power technology, developed to study implosion hydrodynamics, instabilities, turbulence, and material properties in a highly precise, controllable environment at the extremes of pressure and material velocity. The discipline of pulsed power hydrodynamics arose in response to the need for economical, high-precision data to validate sophisticated numerical models used in current numerical simulations and to motivate the development of new models for future simulations. The international capability in pulsed power technology that has evolved over several decades in response to numerous other programmatic needs played a pivotal role in the development of the new discipline by enabling demonstrations of the techniques and production of introductory data long before a dedicated facility could be conceived, planned, and built. The high-precision, cylindrically imploding liner is the tool most frequently used to convert electromagnetic energy into the hydrodynamic (particle kinetic) energy needed to drive strong shocks, quasi-isentropic compression, or large volume adiabatic compression for the experiments. At typical parameters, a 30-gr, 1-mm- thick liner with an initial radius of 5 cm, driven by a current of 20 MA, can be accelerated to 7.5 km/sec producing mega-bar shocks in medium density targets. Velocities up to 20 km/sec and pressures >20 Mbar in high density targets are possible. The Atlas facility, designed and built by Los Alamos, houses the world's first laboratory pulsed power system designed specifically to explore this relatively new family of pulsed power applications. Constructed in the year 2000 and commissioned in August 2001, Atlas is a 24-MJ, high-performance capacitor bank delivering currents up to 30 Megamperes with a rise time of 5 to 6 musec. The first Atlas liner implosion experiments were conducted in September 2001, and 16 experiments were conducted in the first year of operation before Atlas was disassembled to be moved to the Nevada Test Site, where experiments began again in July 2005. Applications of pulsed power hydrodynamics techniques currently include material property topics such as: exploration of material strength at high rates of strain; material failure including fracture, damage, and spall; and interfacial dynamics at high relative velocities and high interfacial pressures. Implosion dynamics and a variety of complex hydrodynamic geometries have been explored and experiments to explore perturbation growth and transition to turbulence are under consideration. Longer term applications include the study of the behavior and properties of strongly coupled plasmas and the equation of state of metals and non-metals at pressures above 10 Mbar. This paper will provide an overview of the programmatic evolution that led to the birth of the discipline of pulsed power hydrodynamics.

The University of Texas at Austin is constructing a spacious facility for research in pulse power technology at the Balcones Research Center, located in north Austin. The arrangement and capacity of the facility are intended to support high-current experiments. The laboratory power supply being designed consists of six homopolar generators, each capable of delivering ten megajoules of energy. The output bus is configured such that various series, parallel, and series-parallel circuits of homopolar generators are possible. Both resistive and inductive loads can be driven from the power supplies. Research programs will be supported with a wide range of physical facilities, including materials handling, machine shop, data acquisition and analysis, engineering and operating personnel, chemical analysis and metallurgical laboratories, and an information center. These facilities will be available to the U. S. technical community through several types of arrangements with The University through the Center for Electromechanics. Each of the six homopolar generators is designed to deliver 1 MA at 100 V, with a maximum repetition rate of a discharge every five minutes. In addition to EM launch research and applications, other intended uses of the power supply include welding of large cross-sections of metal (up to 650 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> or 100 in. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of steel), generation of high magnetic fields in low-impedance magnets, and testing of high-current opening switches. Status of major elements of the project is reported.

Anisakis is a parasite that is found in many marine products and can cause anisakiasis when present in fish consumed raw. The most common way to prevent anisakiasis is to freeze the fish, but this causes a noticeable decrease in the quality of the fish when eaten as sashimi. Although no practical method of killing anisakis other than freezing has been found, we have now succeeded in inactivating anisakis inside the fish meat by repeatedly and instantaneously applying electric current to the fish meat using pulsed power technology. The fish meat was placed in buffer saltwater, and pulsed power was applied multiple times. The immobilization rate was highest when the buffer saltwater was 5 mS/cm. The immobility ratio increased as the number of shots increased. Sensory evaluation of the fish meat after the pulse treatment confirmed that it retained its quality as sashimi. Breaking tests and color measurements were also conducted. We believe that this pulsed power treatment is a useful alternative to freezing as a method for killing anisakis.

In this introduction to the Special Issue on pulsed power and its applications, background information is provided for the nonspecialist to better understand the many challenges in designing pulsed power systems, and the wide diversity of applications that are now emerging. The approach to providing a tutorial on pulsed power technology is to make available to the reader the paper written by J. C. Martin which appeared in a Special Section of the Proceedings of the IEEE on pulsed power technology in June 1992. That paper is supplemented in this introduction with additional information that complements many of the invited papers composing this Special Issue.

Pulsed power systems for directed energy weapon platforms are becoming increasingly important in modern combat situations. A general thermodynamic analytical investigation was developed to assess the impact of technological improvements on mission effectiveness and weapon power generation in an aircraft (a/c) based pulsed power system. The power system, for which the analysis is being conducted, essentially consists of six major components, a prime power source, electrical power generator, power conditioner, pulsed power source and pulsed power processor and the thermal management system (TMS) with a total estimated payload restriction of 4600 kgs., based on a USAF cargo aircraft. The a/c based power systems analysis corresponds to a notional aircraft mission, with the turbo- shaft engine operating at a fixed altitude. It has been assumed that heat from various system components is collected by the same coolant loop, and then rejected to ambient air in a ram air heat exchanger (RAHX). The analysis was based on a Multi-MW class pulsed power source output and a notional mission profile with an engagement period of 60 minutes during which several duty cycle scenarios were considered. The power system components were sized to accommodate the power requirement represented by the respective duty cycle of operation. Several power system architectures were evaluated with a baseline power system model that incorporated current off-the-shelf (OTS) technologies for each component. The baseline power systems analysis was conducted to size a power system for steady state operation at peak load during an individual engagement. A stand-alone turbo shaft engine was used as the primary power source because of its high power density but the engine performance is very sensitive to increasing altitude where the output power diminishes rapidly. As a result of this and the necessity to accommodate load sharing or load following during engagement, the investigations were extended to the hybrid power system architecture with turbo alternator-battery and turbo alternator-flywheel combinations.

Nanosecond pulsed non-thermal atmospheric-pressure plasmas are promising for numerous applications including air and water purification, ozone synthesis, surface sterilization, material processing, and biomedical care. However, the high cost of the nanosecond pulsed power sources has hindered adaptation of the plasma-based technologies for clinical and industrial use. This paper presents a low cost ( 10 kV, a 3 ns rise time (10 to 90 %), and a 10 ns pulse duration (full width at half maximum) at a pulse repetition rate of up to 500 Hz were achieved in the present study. It has been successfully tested to power three different plasma reactors to form pulsed corona discharges, dielectric barrier discharges, and sliding discharges. The energy efficiency of such a nanosecond pulsed sliding discharge system was assessed in the context of ozone synthesis using air or oxygen as the feed gas, and was found comparable to a previously reported non-thermal plasma system that used commercial high voltage pulsed power sources. This study demonstrated that this low-cost nanosecond pulsed power source can prove to be an energy efficient and simple supply to drive various non-thermal atmospheric-pressure plasma reactors for environmental, medical and other applications.

Pulsed power originated with the invention of the Marx bank in the early 1920s, enabling the simulation of lightning strikes and switching operations on power system components. Between the 1960s and the beginning of the twenty-first century, the demands of high energy pulsed power applications have stretched Marx bank techniques enormously. Refinements of triggering and switching techniques, and control and exploitation of the stray capacitances in the systems, enable 100-200 ns rise times to MV levels and above with MJ of energy being stored and delivered. The requirements of exotic radiographic, e-beam and plasma pinch loads have demanded the use of pulse forming networks or lines interposed between the Marx and the load to provide the requisite pulse shaping and power levels. Meanwhile the rise time capability of low energy Marxes has been reduced to nanosecond levels as a result of developments in capacitor and switching technologies. The latest direction is now for the development of ultrafast high energy Marxes with adequately low inductance for direct feed of compact e-beam loads.Pulsed power has principally developed in response to high energy physics and weapons programme requirements; plasma drivers, x-ray drivers, magnetron drivers, laser drivers, ion beam steering and acceleration. However, the industrial application of pulsed power is increasing.

Induction machines have the unique capability of delivering very high current and peak power in a pulsed mode. It was the need for high power for fusion that led Nicholas Christofilus in the 1950’s to invent and build Astron, the first induction accelerator [1]. Since then, various high power applications have led to the construction of the Electron Ring Accelerator (ERA) [2], Experimental Test Accelerator (ETA) [3], Advanced Test Accelerator (ATA) [4], the flash radiography machine FXR and the high repetition rate machine, ETA II [5], which was designed to deliver high average power as well as high peak power. The largest of these machines is ATA with design goals of 50 MeV and 10 kA. All of the high current electron machines since ERA are “short-pulse” devices ( 50 ns). Meanwhile, the invention of heavy ion fusion in the 70’s led to the development of induction machines for ion acceleration [6]. For this application, the devices tend to have long pulses (>1 μs). The induction machines for ions and electrons operate on the same principle. The pulse length difference between electron and ion machines is historical and incidental, although long-pulse devices lead to different approaches to magnetic material and pulse power technology than short-pulse machines. While some of the past applications, particularly those related to the Strategic Defense Initiative, have come and gone, the need for high power continues to exist in energy, environment, national defense, and basic sciences. In this paper, we will review three ongoing applications, one in fusion energy, one in defense, and one in high energy physics. Induction machines for heavy ion fusion [7], for radiography in hydrodynamic tests [8], and for relativistic-klystron twobeam-accelerators [9] are three areas of active research. Induction machines have also been considered for other applications such as treatment of nuclear wastes [10], neutron spallation sources [11], and μμ collider components [12]. These applications will not be reviewed here because of space limitations. In addition, the inductive voltage adder (IVA) technologies are described in a separate paper in these proceedings [13]. The three applications we will review were chosen to demonstrate that with vastly different goals, different machine parameters, and very different architectures, a similar set of performance objectives has led to technological advances along closely parallel paths. In any large machine, the economic issues of cost and efficiency, and the technological issues of machine and beam performance are equally important considerations. We hope to show how these factors have affected the development paths in these three areas. We will first summarize recent activities in each one of these fields, and then proceed to describe issues and advances in the control of beam energy flatness, emittance preservation, and beam instability suppression. While these issues are common to all accelerators, the fact that we are working with very intense beams and long pulses makes the challenges of induction machines unique. For the purpose of this review, we will broadly include the induction accelerators proper, as well as their injectors.

Emulsion polymerization of methyl methacrylate under pulsed microwave irradiation