Akira Tokuchi

Compact solid-State switched pulsed power and its applications

Power semiconductor devices, such as insulated-gate bipolar transistors, metal-oxide-semiconductor field-effect transistors, and static-induction thyristors, are used in different kinds of pulsed power generators developed for different applications. In addition, the semiconductor opening switch is found to have very effective applications in pulsed power generation by inductive energy storage. Semiconductor switches have greatly extended the scales of pulsed power parameters, especially in repetition rate and lifetime. They have also enabled new areas of pulsed power applications, such as accelerators, flue-gas treatment, and gas lasers.

Pulsed Power Generation by Solid-State LTD

A solid-state linear transformer driver stack has been developed to demonstrate pulsed power generation and output pulse shaping. It consists of 30 modules each using 24 power metal-oxide-semiconductor field-effect transistors as switches. The output voltage of the stack is the superposition of the voltage pulse of each module no matter if the modules are switched synchronously or not. In synchronous operation, the output voltages of all modules are added up to reach an output voltage up to ~29 kV with a maximum output current of ~240 A. The pulsewidth is variable in the range of 50-170 ns. On the other hand, by carrying out separate switching of different modules, the output waveform can be varied by performing pulse shaping. The control signals for pulse shaping experiment are generated using an field-programmable gate array board that allows potentially automatic waveform optimization.

Influence of a Circuit Parameter for Plasma Water Treatment by an Inductive Energy Storage Circuit Using Semiconductor Opening Switch

In this paper, we investigate a water treatment method that sprays waste water droplets into a pulsed discharge space. For this method, it is important to apply pulsed voltages with a short pulse width and a fast rise to the electrode to realize high energy efficiency. An inductive energy storage (IES) circuit using a semiconductor opening switch (SOS) outputs pulsed voltages similar to the above-mentioned voltage. We report the characteristics of the water treatment using the IES circuit. The capacitance and inductance in the IES circuit are varied. An increase in the inductance in the secondary circuit of the pulse transformer, results in the formation of pulsed voltages with a longer pulse width; thus, the ratio of the thermal loss to the discharge energy becomes high. However, the energy transfer efficiency improves. Additionally, we vary the maximum current of the SOS, keeping the pulse width constant, by adjusting the capacitance and the inductance. As a result, when the current in the SOS increased, pulsed voltages with a higher peak and a shaper rise are obtained. Further, the pulse width of the voltage and the energy transfer efficiency are not affected by the current in the SOS. Hence, the energy density of the discharge is higher. The increase in the secondary inductance and the forward current increased the energy efficiency of the water treatment system owing to the increase in the energy transfer efficiency and the discharge energy density.

Repetitive Linear Transformer Driver Using Power MOSFETs

A compact pulsed-power generator based on a linear-transformer-driver scheme has been developed and tested. It consists of ten modules using a total number of 350 power metal-oxide-semiconductor field-effect transistors as switches. It is capable of generating a peak output voltage of 9 kV and a peak output current of 175 A, with a pulselength of ~ 42 ns and a repetition rate of 1 kHz. The overall system efficiency is estimated to be ~ 59%.

MHz pulsed power generator using MOSFET

A stacked MOSFET switch has been developed and tested. Commercially available MOSFETs (900 V, 8 A) are used to form the stack of 8 in series and 6 in parallel. Each FET is triggered by an optically coupled signal so that all units are controlled simultaneously by a common trigger circuit. Experimental results have shown that such this stacked MOSFET switch is capable of working under the voltage of 5 kV, turning on and off of 75 A in /spl sim/ 30 ns, at the maximum repetition rate of 2 MHz.

Switching power supply for induction accelerators

A new particle acceleration method using pulsed induction cells was introduced in the super-bunch project at KEK. Unlike conventional RF acceleration, this acceleration method separates functions of acceleration and confinement. As a result, this acceleration method is capable of accelerating a very long bunch of beam or a wide mass range of particles. However, it is necessary to give a very fast pulsed- excitation to the magnetic material to induce an electric field to accelerate particles. Switching power supplies of high voltage output with very fast pulse-operation is one of the most important key technologies for this new acceleration method. Features of switching power supply developed for induction synchrotron is reported. The 31 kW MOSFET switch performed 1 MHz continuous operation with 15 nsec rise time.

Compact pulsed power and its industrial applications

Repetitive pulsed power generation by compact sources is being studied for industrial applications. The research efforts include pulse-compression concept exploration, electrical circuit design and optimization, switching device development and evaluation, and application demonstrations. The basic strategy is to take advantage of solid-state switching devices to achieve compactness, reliability, and high repetition rate of pulsed power systems operating in both capacitive and inductive energy-storage schemes. These solid-state switches include saturable inductors, saturable capacitors, photoconductive semiconductors, and other power semiconductor switching devices, such as MOSFET, IGBT, SiC-FET, and SI-Thyristor.

Repetitive Pulsed Power Based on Semiconductor Switching Devices

Static induction thyristor and silicon-carbide junction FET have been studied for applications to high-voltage modulators that are demanded by a new type of high-energy particle accelerator, the induction synchrotron. The switching characteristics of these power semiconductor devices are evaluated in order to assess their applicability to MHz level repetitive operation.

Investigation for Optimization of an Inductive Energy Storage Circuit for Electrical Discharge Water Treatment

In this paper, we investigated a water treatment method that sprays waste water droplets into a pulsed discharge space. To increase energy efficiency of this method, a pulsed power generator should output a pulsed power of a high peak and a short pulse width and be low circuit loss, high repetition rate, high power, and high stability. An inductive energy storage circuit using a semiconductor opening switch was studied to satisfy the above-mentioned requirement. Initially, effect of turn ratio of a pulse transformer (PT) in the circuit was investigated. Energy transfer efficiency and the pulsewidth of the output voltage increased with the PT turn ratio, resulting in an increase of the efficiency of the water treatment system. Then, the effect of the load impedance was investigated. The result showed that an optimum resistance to maximize the efficiency exists. From these results and a previous experimental report, we concluded that the optimization conditions are summarized below. The turn ratio and the inductance in the secondary circuit should be as high as possible under the condition, which does not output the very long pulse. The impedance of the discharge at an electrode for the water treatment should be a value that maximizes the energy transfer efficiency. Capacitance of capacitors in the circuit should be adjusted to obtain optimal peak voltage for the generation of active species.

High repetition-rate, low jitter pulsed power generator for excimer laser applications

A high repetition-rate pulsed power generator, which uses IGBT as the main switch, has been developed. It generates high-voltage output of 28 kV that can charge a capacitive load of 12 nF in 100 ns. It can be operated at the repetition rate of 6 kHz. A special technique has been applied to the control circuit so that the main storage capacitor is always charged at a constant voltage, even when the output voltage of the charging unit varies for 20%. As a result the timing of the output voltage pulse is stabilized within a range of several nanoseconds. This level of low jitter is considered to be required by the pulsed power supplies for the short-wavelength excimer lasers.