Keiji Nagai

Solvent removal during curing process of highly spheric and monodispersed-sized polystyrene capsules from density-matched emulsions composed of water and benzene/1,2-dichloroethane

This paper describes in terms of the mass of the solvents in the oil, water, and distillate phases the curing process of highly spheric monodispersed 4-mm-indiameter polystyrene capsules of a uniform thickness. It was determined that the water solubility of the solvents is crucial in the solvent selection in order to prepare the capsules by this method. The curing process started from the water/oil/water emulsions, where the boiling temperature and the densities of the oil were well matched by mixing benzene and 1,2-dichloroethane. The masses of the solvents were measured for the oil phases and the distillate and then calculated for the water phase. The analysis of the solvents in the water phase indicated that the process was governed by the kinetics of their dissolving from the oil phase to the outer water phase rather than by the vapor pressure of the solvents in the early stage before the oil phase lost its fluidity.

Photo-reflection and laser-ablation properties of phthalocyanine/perylene derivative bilayer

The photo-reflectance and laser-ablation properties ofa part of an organic solar cell, a perylene derivative and the phthalocyanine (denoted as PV/H 2 Pc) were investigated. The reflectance ofa PV/H 2 Pc bilayerwas higher than the single layer samples of H 2 Pc and PV. Considering the photovoltaic effect in the corresponding solar cell and chemically doped perylene, the present reflection was characterized to be the photo-generated carrier in the PV layer. The present property can be classified into organic reflectance-tunable material, and is useful as a coating material to realize uniform laser ablation. A remarkable difference was observed in laser ablation ofpolystyrene film, in comparison with that of the PV/H 2 Pc bilayer, when 1060 nm laser incident took place on the coating material. Without the coating the laser pulse formed a spiky structure as a trace ofself-focusing, while for the coated film the ablation trace was from the upstream on the axis without a spiky structure. These phenomena are advantageous for the targets of direct-driven inertial fusion energy.

Uniform laser ablation via photovoltaic effect of phthalocyanine/perylene derivative

Abstract A uniform laser ablation was observed in a polystyrene film coated with a photovoltaic perylene/phthalocyanine bilayer when an incident took place at an intensity range of 10 9 –10 10 xa0W/cm 2 ( λ =1064xa0nm, 1.1xa0ns FWHM). Without the bilayer coating, the laser pulse formed spiky structures in the polystyrene film as self-focusing traces of the laser pulse, while for the coated film, the uniform surface ablation trace without the spiky interior structures was observed. In the case of incident of 532xa0nm where the coating material exhibits no reflection, such difference depending the coating was not observed. These phenomena were coupled with the reflection and conduction properties via its photovoltaic effect, and agreed with the required ablation to achieve high-density compression of the fuel capsule for inertial fusion energy (IFE).

Planar shock wave generated by uniform irradiation from two overlapped partially coherent laser beams

Two partially coherent light laser beams, coupled with a random phase plate were focused at an angle of 31.7° with the centers of the beams offset by 250 μm. This produced a relatively uniform (7% root-mean-square) irradiated spot of 400 μm. When this technique was used to produce a shock wave in a copper wedge, a relatively uniform shock of 2 ns duration was produced. In addition, a multilayered flyer plate was accelerated using this method to an average speed of 21 km/s and produced a planar impact on a glass window. It is anticipated that this technique can be used to produce important multi-Mbar equation of state information in future experiments.

Microstructures of ultralow-density foam plastics obtained by altering the coagulant alcohol

The present report describes ultralow density (2–12 mg/cm3) plastic (CH2) foams whose density is close to the cutoff density of the plasma for visible and near-infrared light beams (0.55–1.3 µm). These foams are prepared from a poly(4-methyl-1-pentene) gel with hexanol derivatives by extraction using supercritical fluid CO2. Their intended use is in laser-plasma experiments and as a laser-plasma X-ray source. Their microstructure (2–10 µm) was finer than that of the previous poly(4-methyl-1-pentene) foam and could be varied using different hexanols.

Fast heating of super-solid density plasmas towards laser fusion ignition

We have studied fast heating of highly compressed plasmas using multi 100 TW laser light. Efficient propagation of the ultra-intense laser light and heating of the imploded plasmas were realized with a cone-attached shell target. Energy deposition rate of the ultra-intense laser pulse into high-density plasmas was evaluated from neutron measurements. Generation and propagation property of energetic electrons in the ultra-intense laser interactions were also investigated with solid density targets. About 40% of the laser energy converted to mega electron volts energetic electrons in the interactions with solid targets at intensities of 10 19 W cm -2 . These electrons propagated in the high-density plasmas with a divergence of 20-30° or jet-like collimation. Taking account of these experimental results, heating laser spot size is optimized for laser fusion ignition with a simple estimation.

Activities on target fabrication and injection toward laser fusion energy in Japan

Target-related activities to demonstrate ignition and burn were summarized. Fabrication of foam shells with a gas barrier by emulsion process, understanding of centering mechanism in the emulsion process, coating of organic photovoltaic cell to reduce initial imprint are described. Cooling-induced deformation (CID) of shells was studied and found to be important for thin shells. Results on magnetic levitation, injection and tracking that are necessary to provide targets to the firing position are mentioned.

Time and space-resolved measurement of a gas-puff laser-plasma x-ray source

The dynamic interaction processes between a nano-second laser pulse and a gas-puff target, such as those of plasma formation, laser heating, and x-ray emission, have been investigated quantitatively. Time and space-resolved x-ray and optical measurement techniques were used in order to investigate time-resolved laser absorption and subsequent x-ray generation. Efficient absorption of the incident laser energy into the gas-puff target of 17%, 12%, 38%, and 91% for neon, argon, krypton, and xenon, respectively, was shown experimentally. It was found that the laser absorption starts and, simultaneously, soft x-ray emission occurs. The soft x-ray lasts much longer than the laser pulse due to the recombination. Temporal evolution of the soft x-ray emission region was analyzed by comparing the experimental results to the results of the model calculation, in which the laser light propagation through a gas-puff plasma was taken into account.

Single molecular membrane glue technique for laser driven shock experiments

The present report describes the adhesion of metal foils without a conventional glue to provide a precise thickness (~ 20 µm) of an adhered step target for ultrahigh pressure, laser shock experiments. The technique involves two processes: single molecule coating on the metal surface and fastening the two surfaces together. For the two 20 µm aluminum targets of single foil and adhered foils, a negligible difference in laser shock speed was observed in comparison with laser energy and target thickness.

Influence of Residual Gas on the Life of Cryogenic Target and Trajectory of Injected Targets

Abstract Influence of residual gas in a laser fusion reactor chamber at the time of pellet injection is discussed, including the lifetime of a cryogenic target, the stall by drag force, the deviation by a crosswind and the lift by spin of the pellet. The pellet is assumed to be injected accurately with designated speed and direction every time. Preliminary results indicate that the vapor pressure in the chamber should be less than 0.1 Torr and the shot-to-shot variation in the wind speed must be less than 1 m/s to deliver the fuel pellet at the firing position with an accuracy of 100 μm.