Keisuke Shigemori

Learn More
We have examined the evolution of cylindrically symmetric blast waves produced by the deposition of femtosecond laser pulses in gas jets. In high- Z gases radiative effects become important. We observe the production of an ionization precursor ahead of the shock front and deceleration parameters below the adiabatic value of 1/2 (for a cylinder), an effect(More)
Modern high-power lasers can generate extreme states of matter that are relevant to astrophysics, equation-of-state studies and fusion energy research. Laser-driven implosions of spherical polymer shells have, for example, achieved an increase in density of 1,000 times relative to the solid state. These densities are large enough to enable controlled(More)
Opacity effects on extreme ultraviolet (EUV) emission from laser-produced tin (Sn) plasma have been experimentally investigated. An absorption spectrum of a uniform Sn plasma generated by thermal x rays has been measured in the EUV range (9-19 nm wavelength) for the first time. Experimental results indicate that control of the optical depth of the(More)
We have developed a prepulse-free short-pulse Nd:glass laser system of 0.9-PW peak power to heat a pre-imploded high-density plasma. An optical parametric chirped amplification system is introduced to reduce the prepulses to an amplitude (1.5/spl times/10/sup -8/) of that of the main pulse. The compressor is a double-path grating pair system 94 cm in(More)
To test high gain targets surrogated in the planar geometry, we have constructed a new experimental system (HIPER) which provides the high ablation pressure with a uniform irradiance profile. These performances were achieved by bundling twelve beams of the existing GEKKO XII into a F/3 focus cone. The partially coherent light is introduced for the beam(More)
Laboratory generation of strong magnetic fields opens new frontiers in plasma and beam physics, astro- and solar-physics, materials science, and atomic and molecular physics. Although kilotesla magnetic fields have already been produced by magnetic flux compression using an imploding metal tube or plasma shell, accessibility at multiple points and better(More)
The growth rate of the ablative Rayleigh-Taylor instability is approximated by gamma = square root[kg/(1 + kL)] - beta km/rho(a), where k is the perturbation wave number, g the gravity, L the density scale length, m the mass ablation rate, and rho(a) the peak target density. The coefficient beta was evaluated for the first time by measuring all quantities(More)
We performed integrated experiments on impact ignition, in which a portion of a deuterated polystyrene (CD) shell was accelerated to about 600 km/s and was collided with precompressed CD fuel. The kinetic energy of the impactor was efficiently converted into thermal energy generating a temperature of about 1.6 keV. We achieved a two-order-of-magnitude(More)
Developments in measuring sound velocity of matter under ultrahigh pressure are described. We employed a time-resolved x-ray shadowgraph technique to measure the sound velocity of shock-compressed diamond and iron foils at around melt. The sound velocity significantly dropped at melting, a behavior that has been difficult to clarify by conventional(More)
Recent progress of impact ignition is reported: First, a maximum velocity ∼ 1000 km/s has been achieved under the operation of NIKE KrF laser at Naval Research Laboratory (laser wavelength = 0.25μm) in the use of a planar target made of plastic. Two-dimensional simulation have been performed for burn and ignition to show the feasibility(More)