A novel toroidal mirror with an absolute minimum magnetic field configuration (absolute Min-B) using superposition of quadrupole field is proposed. The particle confinement ability of the magnetic configuration is examined and shown to be excellent.

View full abstract

With a neutral beam injected perpendicularly and a strong ion cyclotron range of frequency heating in the magnetic mirror configuration, high beta plasmas with a strong temperature anisotropy are frequently produced. Unstable Alfvén ion cyclotron (AIC) waves are driven with such a strong temperature anisotropy. A magnetic mirror field is the common configuration in fusion devices and also in the space plasmas. The interactions between spontaneously excited AIC waves and plasmas are clearly observed in the laboratory plasmas. The upper bound on the ion temperature anisotropy is imposed by the pitch angle scattering resulting from the excitation of AIC waves. A clear understanding of AIC waves is essential to the study of behaviors of high beta plasmas in the magnetic mirror configuration. In this report, recent experimental observations related to AIC waves are described.

View full abstract

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.

View full abstract

In order to explore the effect of Pulsed Electric Fields (PEF) with pulses on the order of the charging time of bacterial membranes, we studied the effect of 45 ns pulses on the viability of bacillus subtilis in its vegetative state. A 30 Ω Blumlein generator with a low inductance spark gap switch delivers square wave voltage pulses of 45 ns duration to the electrodes in the bacterial treatment chamber. The rise time, which was varied from 2 ns (f< 200 MHz) to 20 ns (f< 50 MHz), determines the high frequency components in the Fourier spectrum of the pulse. Among pulses of different rise times, having the same total energy, those with the shortest rise time were found to kill bacteria more effectively. These results indicate that the high frequency components in the PEF deposit the electrical energy in the cell and affect intracellular structures.

View full abstract

Pulsed power has been used to produce non-thermal plasmas in atmospheric pressure gases that generate a high electric field at the tips of streamer discharges, where high energy electrons, free radicals, ultraviolet rays, and ozone are produced. These manifestations of streamer discharges have been used in the treatment of exhaust gases, removal of volatile and toxic compounds such as dioxin, and the sterilization of microorganisms. Here, large volume streamer discharges in water are described. These streamer discharges in liquids are able to produce a high electric field, high energy electrons, ozone, chemically active species, ultraviolet rays, and shock waves, which readily sterilize microorganisms and decompose molecules and materials. An application of this phenomenon to the cleaning of lakes and marshes is also described.

View full abstract

Cryptosporidium contaminates most surface waters around the world. It is difficult to remove through conventional treatment processes, and is extremely resistant to the method of chemical disinfection typically used to inactivate these microorganisms. We have developed a new technology for inactivating Cryptosporidium oocysts by using a pulsed arc discharge in water, which creates shock waves, UV emissions, and radicals. The pulsed arc is generated between two cylindrical stainless steel rod electrodes, 6 mm in diameter, and 2 mm apart. We applied this method to the inactivation of oocysts in backwash water from a sand-filter unit of a drinking water plant. The results indicate that the major factor influencing inactivation is UV emissions, and that more than 99% of the oocysts in the high turbidity backwash water (80 NTU) are inactivated with an energy of 0.24 kWh/m³.

View full abstract

Nitric monoxide (NO) is increasingly being used in medical applications. Current applications use a gas cylinder of N₂ mixed with a high concentration of NO. This arrangement is potentially dangerous, given the possibility of an accidental leak of NO from the cylinder. The presence of NO in air leads to the formation of nitric dioxide (NO₂), which is toxic to the lungs. Therefore on-site generation of NO would be very desirable to treat patients with acute respiratory distress syndrome and other related illnesses. Recently, pure NO was generated using a pulsed arc discharge in dry air with an NO₂-NO converter and charcoal. The concentration of NO was easily controlled by controlling pulse repetition rate and gas flow rate. This system is already under investigation in an animal experiment.

View full abstract

Pulsed high voltage was applied to logs used for mushroom culturing to mushroom growth. An experiment was carried out in an attempt to increase shiitake mushroom yield. Results showed that the weight of shiitake mushroom yield was double that of a normal group cropped in a month. Another experiment was performed to estimate the effect of electrical stimulation on the growth of hyphae. Results of that experiment showed a slight influence on the growth of hyphae, and showed some possibilities this method can improve mushroom culturing techniques.

View full abstract

In electron interactions with highly charged Fe ions, the X-ray spectra were theoretically analysed and compared with the experimental results at the Tokyo EBIT. In the present analysis, cross sections for dielectronic recombination, resonance excitation, resonance recombination, and direct excitation were calculated by use of the distorted wave method. Simulated spectra were obtained by convoluting the calculated cross sections with the experimental beam energy resolution and X-ray detector resolution, which are in close agreement with the experimental observations. Based on our calculations including polarization effects, we estimate the charge state balance: He-like Fe²⁴⁺ (74%), Li-like Fe²³⁺ (18%), and Be-like Fe²²⁺ (8%), and the ion density in the trap to be 6.5−8.5 × 10⁸ cm^-3. The present calculations were also compared with the previous high-resolution measurements of the KLL resonances in He-like Fe ions.

View full abstract