Kazuo Hayashi

Charge exchange neutral particle mass and energy analyzer for the JT‐60 tokamak

Design considerations and experimental results are described for a charge exchange neutral particle mass and energy analyzer for JT‐60, which analyzes H, D, and He simultaneously up to a maximum energy of 110 keV. The analyzer has separately a 180° deflection magnet for momentum analysis and an electrostatic deflector for mass analysis. The way to control the effect of the electric fringe fields in order to expand the detectable energy range is studied by numerical simulation. The deflector is then designed, made of two triangular plates and three additional electrodes for the control of the fringe fields. The effect of the deflector is demonstrated experimentally. Energy and mass resolution and the relation between the incident ion energy and the magnetic field strength are measured. The results of the calibration experiments agree with the designed value.

Temperature Dependence of Toluene Decomposition Behavior in the Discharge-Catalyst Hybrid Reactor

Temperature dependence of toluene decomposition behavior was investigated with a two-stage discharge and ozone-catalyst hybrid reactor. Temperature was varied from 20 to 200degC because VOC exhausts from painting and printing facilities reach this temperature level. A synergistic effect of discharge and catalysts was observed for toluene conversion at temperatures lower than 200degC. In the hybrid reactor, COx formation was promoted compared to discharge alone, and toluene was completely oxidized to COx at higher than 100degC.

Multi-Channel Mass-Separated Neutral Particle Energy Analyser for Simultaneous Measurements of Hydrogen and Deuterium Atoms Emitted from Tokamak Plasma

A mass-separated neutral particle energy analyser able to carry out the simultaneous measurement of hydrogen and deuterium atoms emitted from a tokamak plasma was constructed. The analyser was calibrated for the energy and mass separation in the energy range from 0.4 keV to 9 keV. It was installed in the JFT-2 tokamak in order to investigate the behavior of deuterons and protons in a JFT-2 tokamak plasma heated by ion cyclotron wave and neutral beam injection. It was found that the energy spectrum could be determined with sufficient accuracy, and the ion temperature obtained from the energy spectrum was in good agreement with the ion temperature deduced from the Doppler broadening of the impurity ion line.

Radon concentration dependence of alpha radioactivity measurement using ionized air transportation

We are developing an alpha radioactivity measurement apparatus for uranium contaminated waste with large and complex surfaces (alpha-clearance monitor). This monitor uses the alpha radioactivity measurement method using ionized air transportation. Our goal of the monitor is to measure 4 Bq of alpha radioactivity for a 10 minutes measurement (5.7 Bq at present). A problem in achieving the goal is fluctuation in the background (BG) ion current. This fluctuation is predicted to be mainly due to radon inside the monitor. Therefore we developed a method to measure the radon concentration inside the monitor without an additional radon detector which disturbs airflow. And as a preliminary study, we determined the radon contribution to the BG current using this method. In addition, ion mobility and ion recombination coefficient, which are the other factors influencing the detection limit, were measured and evaluated under various environmental conditions (temperature, humidity and aerosol density).

Development of a 10-kW solid state pulse power supply for copper vapor lasers

We have developed a magnetic-pulse-compression-type 10-kW-class solid state pulse power supply for copper vapor lasers. By triggering the gates of two gate turn-off thyristors (GTOs) connected in parallel, a 5-μs rise time primary pulse was generated. A three-stage magnetic pulse compression circuit compressed the primary pulse to 0.13 μs. The 13.7-kW GTO switching energy was achieved with a 4-kHz pulse repetition rate when a dummy load was connected instead of copper vapor laser (CVL). Total energy transfer efficiency of the power supply was 60%. This pulse power supply has been applied to a CVL with a plasma tube of 70-mm inner diameter and 1.5-m discharge length, and has operated successfully.

Copper density measurement of a large-bore CVL

The ground state and the lower laser level copper densities were measured in a large-bore copper vapor laser (CVL). The beam diameter was 80 mm, the discharge length 1500 mm, and the output power about 100 W at an operation of a repetition frequency 5 kHz. A new laser-absorption method has been developed to measure the copper ground state density. The measured copper density of the ground state was 1 to approximately 5 X 1021 m-3 and the radial profile was hollow. The profile can be explained from the radial gas temperature profile. The lower laser level (metastable state) densities were measured by the ordinary laser-absorption method. The density of the lower laser level for green emission was about 1 X 1018 m-3 and that for yellow emission was about 3 X 1017 m-3 at the center. The lower laser level densities were higher at the center than near the wall in contrast with the ground state density.

Airflow produced by dielectric barrier discharge between asymmetric parallel rod electrodes

We observed a novel type of airflow produced by an atmospheric rf discharge between asymmetric parallel rod electrodes. The electrodes were a bare metal rod 1 mm in diameter and a glass-coated metal rod 3.2 mm in diameter. The thrust, measured by a pendulum, increased with discharge input power.

Development of solid state pulse power supply for copper vapor laser

The authors have developed a magnetic-pulse-compression type solid-state pulse power supply. The lifetime of a solid-state device is expected to be much longer than that of a thyratron. Two parallel connected gate-turn-off thyristors generated a long pulse, which was compressed to 0.27 microsecond(s) ec by a three-stage magnetic pulse compression circuit. The average power of 8.2 kW was able to be obtained when a dummy load was connected instead of copper vapor laser (CVL). This pulse power supply has been applied to a CVL with a plasma tube of 70 mm inner diameter and 1.5 m discharge length, and has been successfully operated.

Output characteristics and improvement in beam-profile of large-bore copper vapor lasers

Alumina plates (Gas-cooling plates) were inserted into the plasma tube of copper vapor lasers to cool the buffer gas at the center of the plasma tube. Consequently, the laser intensity increased, especially at the center, and higher output power was obtained. It was revealed by measurement that the gas-cooling plates reduce the buffer gas temperature and the lower laser level density of copper atoms at the center of the plasma tube. Output characteristics were measured by varying the repetition frequency. Plate insertion improved the central intensity at higher frequencies. Output power was most dependent on the frequency with the plate inserted, and increased proportionally as the frequency increased.

The method of ion current measurement on capacitive-coupled plasma

A small device, the conduction current probe, has been developed for the multi-point observation of ion currents. The probes are mounted on an electrode of a capacitive-coupled rf plasma source. The probe obtains the conduction current entering the electrode as a function of time by shielding the rf displacement current. The conduction current consists of the ion current as well as the electron one. The ion current is nearly constant although the electron one synchronizes with the rf electric field and flows in the short time of a rf cycle. Therefore, the ion current is obtained from the constant region of the conduction current. The experiments on a rf magnetron have revealed that the probe is a useful device for studying the parametric properties of the plasma source.