Chikara Konagai

Active Beam Scattering Method for Measurement of Ion Temperature in JFT-2 Tokamak Plasma

The capability of determining ion temperature by neutral beam scattering was investigated, and the ion temperature of an ohmically-heated JFT-2 tokamak was determined using a neutral beam scattering system. In the scattering experiment, a continuous beam of 15 keV hydrogen atoms was used with a scattering angle of 4°C. The ion temperature obtained by this method agreed with that deduced from measurement of passive charge-exchange neutrals. The influence of impurities on the scattering spectrum was investigated, and it was found that the difference between the intensity estimated from Rutherford scattering theory and the observed intensity increased with the atomic number of the target particle. It was established that the fact that impurity ions did not contribute to the scattering intensity arose from the ionization of the neutral beam by collision with impurity ions.

Underwater Direct Metal Processing by High-Power Copper Vapour Laser

Copper Vapour Lasers (CVLs) have been applied to underwater direct metal cutting and surface stress improvement. CVL’s features of high peak power, high repetition rate and visible wavelength enable fast, clean and thermal-effect free processing. The CVL based processing is expected as an alternative repairing or maintaining method in nuclear facilities.

High-power copper vapor laser development

Copper vapor laser (CVL) devices of 60 mm bore have been developed for atomic vapor laser isotope separation, and recently an average power per device of over 200W (211W maximum) has been achieved by expanding the discharge length to 3000 mm. In order to further improve the power output by increasing the discharge volume, it is important to supply discharge energy efficiently to the laser tube and to maintain the optimum copper vapor density in the larger volume. Now a CVL discharge circuit has been designed using a CVL discharge simulation code able to calculate time-dependent plasma resistance. In addition, a thermal insulation structure that effectively maximizes the laser gain volume has been designed using a thermal simulation code that takes thermal conduction and emission loss from the tube ends into account. This code yields results which show good agreement with experimental data. The results demonstrate that codes which simulate electrical and thermal characteristics are effective tools in the design of high-power CVL devices. In this paper, the methods of designing CVL electrical circuits and laser head structures using CVL simulation codes are reported, and some resulting high-power devices are discussed.

Analysis of trace metal elements in water using laser-induced fluorescence of laser-breakdown plasma

Laser induced breakdown and laser-excited atomic fluorescence spectroscopy were used to analyze trace metal atoms in water. Laser breakdown plasma was generated by a Q-switched Nd:YAG laser and an optical parametric oscillator (OPO) laser was used to excite target atoms in water. The wavelength of second laser was tuned to the absorption line of the target atom, and its time delay from the first one was optimized in order to maximize the fluorescence signal under low background light. Furthermore, the optimum transition lines were selected in terms of oscillator strength, branching ratio, and level population of target atom. In the case of Fe doped solution, the Fe concentration of less than a hundred ppb was detected. With this method, a lower detection limit of Fe was achieved than that in the case of the method using only laser-induced breakdown spectroscopy. The developed system is applicable for quick and supersensitive detection of trace metal atoms in water.

Laser system for isotope separation

Atomic vapor laser isotope separation (AVLIS) is regarded as the most promising method to obtain srightly enriched economical nuclear fuel for a nuclear power plant. However, achieving a high power laser seems to be the bottle neck in its industrialization. In 1985, after successful development of high power lasers, the U.S. announced that AVLIS would be used for future methods of uranium enrichment. In Japan , Laser Atomic Separation Enrichment Research Associates of Japan (LASER-J), a joint Japanese utility companies research organization, was founded in April, 1987, to push a development program for laser uranium enrichment. Based on research results obtained from Japanese National Labs, and Universities , Laser-J is now constructing an AVLIS experimental facility at Tokai-mura. It is planned to have a 1-ton swu capacity per year in 1991. Previous to the experimental facility construction , Toshiba proceeded with the preliminary testing of an isotope separation system, under contract with Laser-J. Since the copper vapor laser (CVL) and the dye laser (DL) form a good combination , which can obtain high power tunable visible lights ,it is suitable to resonate uranium atoms. The laser system was built and was successfully operated in Toshiba for two years. The system consist of three copper vapor lasers , three dye lasers and appropriate o Atomic vapor laser isotope separation (AVLIS) is regarded as the most promising method to obtain srightly enriched economical nuclear fuel for a nuclear power plant. However, achieving a high power laser seems to be the bottle neck in its industrialization. In 1985, after successful development of high power lasers, the U.S. announced that AVLIS would be used for future methods of uranium enrichment. In Japan , Laser Atomic Separation Enrichment Research Associates of Japan (LASER-J) , a joint Japanese utility companies research organization , was founded in April, 1987, to push a development program for laser uranium enrichment. Based on research results obtained from Japanese National Labs, and Universities, Laser-J is now constructing an AVLIS experimental facility at Tokai-mura. It is planned to have a 1-ton swu capacity per year in 1991. Previous to the experimental facility construction, Toshiba proceeded with the preliminary testing of an isotope separation system, under contract with Laser-J. Since the copper vapor laser (CVL) and the dye laser (DL) form a good combination, which can obtain high power tunable visible lights, it is suitable to resonate uranium atoms. The laser system was built and was successfully operated in Toshiba for two years. The system consist of three copper vapor lasers, three dye lasers and appropriate optics. With pertinent electronics, the system total out put is 3 watts at 5 kHz repetition rate. For each CVL-DL laser set, the CVL output power was designed and operated at 20 watts and fed into DL to obtain 1 watt output. The CVL-DL sets provide three different wave lengths. Accurate wave mixing and laser pulse timing are also required during the experiment. Those laser systems, designed and manufactured in Toshiba, satisfactorily maintained a total operation time of 2000 hours during the past two years. Design work and operating experience for this laser system are described in this paper.

Application of silicon surface barrier detector for fast neutral particles

A design study of a small‐size neutral particle analyzer using a silicon surface barrier detector (SSD) is performed. The SSD is very sensitive to x rays or photons, so that a pair of 45° sector magnets to separate a reionized neutral from x rays and photons will be used for this analyzer. In order to examine the performance, the SSD was applied to measure the species ratio of the prototype neutral beam injector for JT‐60. It was confirmed that the energy resolution was 12% at 40 keV and the linear relation between the incident energy of particles and the pulse height was held over the energy range from 16.7 to 100 keV. The species ratio measured by the SSD was in good agreement with that by the Doppler‐shift spectrometer. The SSD has a sufficient capability for the energy analysis of fast neutrals.

Neutron radiography used on a mono-propellant thruster

Most mono-propellant thruster technologies were developed in the 1960s and the basic principles and fundamental structures, such as the catalyst and propellant, have remained in use without major technical innovation. Conversely, much remains to be identified in terms of the concrete mechanisms and quantitative limitations of the phenomena inside the monopropellant thruster. One of our studies to improve the reliability of propulsion systems involved visualization, facilitating the direct observation of the physical and chemical phenomena occurring within the catalyst bed of the mono-propellant thruster. In this paper, we introduce the visualization test results of the mono-propellant thruster utilizing Neutron Radiography. This paper shows an overview of the non-destructive imaging technique using Neutron Radiography and the visualization hot-firing test result of the mono-propellant thruster through the application of Neutron Radiography.

X-ray Visualization of Carbon-Particle Oxidation Process in Supercritical Water

A real-time X-ray visualization system for low X-ray absorption materials has been developed. The system is mainly composed of a multi-color scintillator based image intensifier and a real-time image-processing unit. The color image intensifier has such advantages as the high sensitivity, the wide dynamic range and the long lifetime over the conventional one. The dynamic imaging of low X-ray absorption materials was realized by the video-rate image subtraction function of the image processor. The system has been successfully applied for an observation of a carbon-particle oxidation process in supercritical water. The low X-ray absorption difference between carbon and supercritical water, surrounded by high X-ray absorption metal wall, is one of the most difficult objects to get good image. In our system, the carbon-particle image was taken at a 30 frame/sec video-rate by continuously subtracting the background image until at the instance of the carbon-particle disappearance by oxidation.

Development of high-power dye laser chain

Copper vapor laser (CVL) pumped dye laser (DL) system, both in a master oscillator power amplifier (MOPA) configuration, has been developed for Atomic Vapor Isotope Separation program in Japan. Dye laser output power of about 500 W has been proved in long-term operations over 200 hours. High power fiber optic delivery system is utilized in order to efficiently transport kilowatt level CVL beams to the DL MOPA. Single model CVL pumped DL oscillator has been developed and worked for 200 hours within +/- 0.1 pm wavelength stability. Phase modulator for spreading spectrum to the linewidth of hyperfine structure has been developed and demonstrated.

Development of high-power copper vapor laser system

A high power copper vapor laser (CVL) system in master oscillator power amplifier configuration has been developed for laser isotope separation program in Japan. Maximum output power of 650 W has been successfully achieved with 9- cm diameter and 350 cm discharge length amplifier. Also MOPA output power of 2.4 kW has been demonstrated in small master oscillator with 4 cm bore and 4 stage power amplifier with 9 cm bore configuration. The authors developed a thermal calculation code to maintain an optimum copper vapor density throughout a large volume and a new thermal insulation structure design method has been proposed to combine two different heat insulators to make longitudinal temperature distribution of the laser tube as flat as possible. A CVL discharge circuit has been improved by applying an excellent magnetic switch which prove a approximately 90 kV-4000 A pulse to a CVL at 4.4 kHz repetition rate. This paper reports such CVL design methods together with the performance of the designed high power CVL system.