Kiyohisa Terai

Magnetically insulated and inertially confined fusion — MICF

By combining the benefits of magnetic and inertial fusion, a new fusion scheme is proposed. A plasma with a density of ?1021 cm?3 is confined by the inertia of a heavy, cannonball-type metallic shell; its heat is insulated by a self-generated magnetic field of ?100 T. The plasma and the magnetic field are produced by ablation due to direct impact of a laser (or particle) beam on solid fuel which constitutes the coating of the inner surface of the spherical metallic shell. Preliminary experimental and simulation results, using a 100 J CO2 laser on a target of a few millimetre parylene shell, gave n? ? 5 ? 1012 cm?3?S, with T ? 500 eV. A 1-D spherical hydrodynamic code, HISHO, with the radial heat conductivity reduced by an assumed magnetic field of 103 T, leads to ignition at an absorbed energy of the order of 20 MJ deposited during a confinement time of approximately 100 ns. These results provide supporting evidence for the feasibility of the scheme as a realistic reactor.

The LEKKO VIII CO 2 gas laser system

The eight-beam CO 2 laser system, LEKKO VIII, producing 10 kJ for the inertial confinement fusion (ICF) research, has been completed. Advanced techniques developed with the LEKKO II 1 kJ laser have been fully implemented; such as a new type of laser gas, suppression of parasitic oscillation, and automatic operation of the system. A concept for a 100 kJ laser is examined as a feasible module design for a 1 MJ system.

Lateral transport of hot electrons on a spherical target by 10.6‐μm CO2 laser irradiation

Lateral transport of hot electrons on a spherical target irradiated with two beams of CO2 laser (4.8×1014 W/cm2) is studied by spatially resolved Kα x‐ray measurements. The hot‐electron energy and spatial distribution in the target are found to depend on the method of irradiation: tight and overlapped focusing conditions.

Hot Electron Energy Distribution in One-Dimensional Cannonball Target at 10.6 µm Laser Wavelength

Hot electron energy distribution in one-dimensional Cannonball target irradiated by a 10.6 µm laser pulse was investigated by using a multilayered foil technique. The experimental results suggested that the energy distribution of hot electrons in the Cannonball target was quite different from that in the simple planar target. We found that the high energy tail was truncated due to the effects of the presence of front disk in the Cannonball assembly. It is expected that Cannonball targets can quite effectively suppress the hot electron preheating at 10.6 µm laser wavelength.

High Intensity UV Emission from Cold-Cathode Mercury-Argon Lamps

A high-intensity UV light source is required in the fields of bacilli sterilization, material processing and so on. When a continuous sinusoidal voltage waveform is applied between the electrodes of a mercury-argon lamp, the UV emission shows saturation effect because of the presence of a resonance line of mercury. We tried to control the plasma condition by using a pulsed power supply. The cold-cathode mercury-argon lamp used was 180 mm long and 6.0 mm in diameter. A square-like pulsed waveform whose frequency and duration were 70 kHz and 5 µs, respectively, was alternately applied between the electrodes. As a result, the 254 nm UV emission intensity was achieved, which was 30-fold that obtained by applying 30 kHz continuous sinusoidal waveform.

Implosion Property of Cannonball Target at 10.6 µm Laser Wavelength

Compressed core density of a Cannonball target of inner pellet irradiation type at 10.6 µm laser wavelength was measured using spectrally resolved neon X-ray emission. The implosion simulations by HIMICO code agreed well with the experimental results and showed that the dominant force of implosion is hot electron driven ablation pressure. Comparison of the simulation and experimental results clarified that the core density was compressed to 200 mg/cc due to the truncation of high energy electrons. We show that the hot electron driven Cannonball target is a feasible scheme for high density compression at 10.6 µm CO2 laser.

Fundamental Studies on One-Dimensional Cannonball Targets at 10.6 µm Laser Wavelength

A new scheme for the inertial confinment fusion (ICF) pellet, called a Cannonball target, has been investigated experimentally using a 10.6 µm laser. The fuel pellet is surrounded by a tamper with a vacuum between the two, and the laser energy is introduced into this space through a small hole in the tamper. The fundamental properties of the Cannon-ball target, such as its absorption and hydrodynamics, and the emission spectra of ions and electrons, have been investigated. The results show a good absorption of 50% and a high hydrodynamic efficiency of 16%. It was found possible to suppress hot-electron preheating.

Generation of Long Life Plasma and Strong Magnetic Field by CO2 Laser

Long life plasma is generated when a focused CO2 laser beam is injected into a cavity.1) A hot core of plasma is observed at the center of cavity separated from the surface of the cavity wall. The temperature is measured to be 300 ~ 600 eV by X-ray spectroscopy and filtered X-ray diode. The life time of the plasma, 10 ~ 30 ns, is much longer than the cooling time by the thermal conduction.

Hot Electron Energy Distribution in Spherical Cannonball Target at 10.6 µm Laser Wavelength

Hot electron energy distributions in spherical Cannonball targets at 10.6 µm laser wavelensth were measured using the multi-layered target technique and the Monte Carlo electron transport code. In the inner pellet irradiation type of target, a high energy component of the hot electron energy distribution is strongly reduced from Maxwellian, leading to lower preheating.