Shuzaburo Takeda

High-efficiency operation of chemical oxygen-iodine laser using nitrogen as buffer gas

High-efficiency operation of supersonic chemical oxygen-iodine laser (COIL) with an advanced jet-type singlet oxygen generator using nitrogen as buffer gas was demonstrated. Laser output was remarkably increased when buffer gas was cooled with liquid nitrogen. The effects of buffer gas temperature on the characteristics of the oxygen-iodine laser medium was discussed. A net chemical efficiency of 23.4% was obtained at 405 W when the chlorine molar flow rate was 19 mmol/s.

Output Power Enhancement of a Chemical Oxygen-Iodine Laser by Predissociated Iodine Injection.

Output power enhancement of a chemical oxygen-iodine laser (COIL) by an injection of predissociated iodine was studied. Iodine molecules were dissociated into atoms by the microwave discharge prior to injection. It was determined that predissociation caused a negative effect on the output power enhancement when this technique was applied to a conventional supersonic COIL. Model calculations revealed that the existence of atomic iodine at the plenum caused the dissipation of stored energy. It was demonstrated that decreasing the mixing point pressure was crucial to obtain output power enhancement by the predissociation technique. For this purpose, a low-pressure transonic mixing scheme with a grid nozzle array was developed. A 9% enhancement of output power was demonstrated.

Two-dimensional simulation of an unstable resonator with a stable core

An optical resonator simulation code based on the idea of a partially coherent optical field has been developed and used to optimize the design parameters of an unstable resonator with a stable core. The resonator was intended for use with low-gain, large-bore lasers, such as the chemical oxygen-iodine laser (COIL). First the design parameters of the resonator were optimized by the simulation code; then a set of mirrors was fabricated for a small-scale COIL. A 14-W output with M(2) = 29 was obtained. The experimentally obtained results were in good agreement with calculations.

High-efficiency chemical oxygen–iodine laser using a streamwise vortex generator

A supersonic expansion nozzle has allowed us to achieve highly efficient operation of the supersonic mixing chemical oxygen–iodine laser (COIL). The nozzle’s shape produced a rapid mixing of the primary and secondary flows. Made up of a series of thin alternating wedges placed adjacent to each other, the nozzle looks like the letter X when it is viewed from the side. Iodine is injected at the exit plane of the nozzle and is strongly entrained by the streamwise vortices generated by the nozzle. 599 W of output power with a chemical efficiency of 32.9% is obtained, values higher by a factor of 1.4 than those of the conventional COIL.

Parametric study of a twisted aerosol-type singlet oxygen generator

A twisted aerosol singlet oxygen generator (TA-SOG), which is a new high-pressure SOG for the supersonic chemical oxygen-iodine laser (COIL), was developed. Its operational characteristics were compared to those of a conventional liquid-jet-type singlet oxygen generator. It was shown that TA-SOG is operated at an internal gas velocity of 85 m/s, which is three times higher than that of the jet-type SOG. Cl/sub 2/ utilization of 70% and singlet oxygen O/sub 2/ (/sup 1//spl Delta/) yield of 85% were obtained under this condition. The results of our two-dimensional model calculation suggested that there must be some enhancement of a specific surface area in the reaction zone. The mechanism of this effect is discussed.

Output power enhancement by the injection of dissociated iodine in supersonic chemical oxygen-iodine laser

Iodine molecule was dissociated prior to injection in supersonic Chemical Oxygen-Iodine Laser (COIL). In some cases, output power enhancement was observed. However, the output power was decreased at the optimum titration (iodine/oxygen ratio). A quasi-two dimensional simulation was employed to analyze the effect ofiodine pre-dissociation. It was revealed that the high iodine atom concentration at the plenum is responsible for the power reduction. The method to improve the output power by pre-dissociation is discussed.

Performance of high-power lasers for rock excavation

Rock excavation experiment with a 10kW-class CO2 laser was demonstrated as a basic study for field application of high power lasers. Sample rocks used in this experiment as a workpiece were tuff breccia and granite. Effect of assist gases on the excavation rate was surveyed. Oxygen, nitrogen, and air were examined and found not to be useful. It was because the gas flow could not blow the molten rocks off, but only helps to cool in case the hole races certain depth. Excavation rate on both rocks for a various output powers was measured to determine thermal constants inherent to each rock. It was found that the excavation rate resulted in slower, as the hole becomes deeper, because of the deterioration in evacuation efficiency of the molten rock. Thermal parameters of the both rocks were derived from the experimental results. Using simplified thermal balance model, it was estimated that a 50 kW-class mobile laser system has a potential to outperform the conventional mechanical excavation technique.

History of COIL development in Japan: 1982-2002

A twenty-years of COIL researches and developments in Japan are reviewed. The researches of four major sites, namely, Keio University, Industrial Research Institute, Kawasaki Heavy Industries and Tokai University are presented in order of time. Epoch-making works are highlighted, and the significance of those works in the industrial COIL development is discussed, Finally, current status of COIL researches in Japan is introduced.

High-pressure pulsed COIL assisted with an instantaneous production of atomic iodine

A new strategy for pulse oscillation of chemical oxygenNiodine laser based on a combination of a porous pipe SOG with an instantaneous atomic iodine generation, has been developed to seek the potential of COIL as an amplifier of the nuclear fusion driver. This new scheme allows one to produce a large aperture high pressure laser medium, which is favorable to the laser amplifier, while maintaining a minimum degradation of stored energy by water vapor. The experimental apparatus consists of the porous pipe SOG, an iodine donor (CH3I) injector, a flash lamp for the iodine dissociation, and an optical resonator. Operational characteristics of the apparatus including dependence of output energy on an iodine concentration was studied. As the result, the maximum output energy of 800mJ was obtained. It was also found that the CH3I was dissociated through unidentified chemical reaction associated with the O2(1AE).

Industrial and reverse-industrial applications of COIL

The proposal about using COIL not only for industry but also for reverse-industry such as decommissioning are discussed.