Nob. Harada

Foil Acceleration by Intense Pulsed Ion Beam Ablation Plasma

High pressure, high temperature ablation plasma produced by intense, pulsed, ion-beam has been used to accelerate thin foil target. Pulsed ion beam with energy density in the range of 100 ∼ 4000 J/cm2 was irradiated on aluminum target with thick of 50 ∼ 100µm. The time-of-flight technique was used to measure the velocity of the accelerated target foil. The maximum target velocity of ∼ 7.7 km/s was obtained. The ablation pressure obtained from the target speed was ∼13 GPa. The target velocity was found to be almost proportional to beam energy density. As an application of the high pressure generated by ablation plasma, the crystalline structure characteristics of hexagonal boron nitride (h-BN) was studied under the irradiation of pulsed ion beam.

Isochoric heating of foamed metal using pulsed power discharge as a making technique of warm dense matter

To generate well-defined warm dense state for evaluating electrical conductivity by using pulsed-power discharge, we have proposed an isochoric heating of foamed metal. Isochoric heating can be achieved by surrounding the foamed metal with a rigid-walled sapphire capillary. We evaluate the temperature and electrical conductivity of the foam∕plasma based on the line-pair method of the foam∕plasma emission and on the voltage-current waveforms. The electrical conductivity observed agrees with previous experiments and predictions. Thus, the proposed technique yields the electrical conductivity of warm dense matter with a well-defined temperature.

Study of a Disk MHD Generator for Nonequilibrium Plasma Generator (NPG) System

Abstract Design and performance prediction studies of a disk type magnetohydrodynamic (MHD) generator which is applied to the non equilibrium plasma generator (NPG) system have been performed. The main objective of the present study was to find out whether a sufficiently high output performance demonstration is possible with the disk generator which is planned to be used for the NPG-MHD disk pulse power demonstration. A present numerical simulation showed that the original constant height channel could provide not more than 20% of enthalpy extraction because its channel shape could not sustain the working plasma in the stable regime against ionization instability throughout the channel. We concluded that, in order to obtain much higher generator performance, a detailed design of the channel shape was necessary. Design work has also been performed based on the concept that the local electron temperature must be kept at 5000K, i.e. the plasma must be controlled to locate at the center of the stable regime. With the designed channel, enthalpy extraction of up to 40% and output power of 7.2 MW can be successfully expected under the thermal input of 18 MW. In addition, the designed channel requires no major modification of the supersonic nozzle, the inlet swirl vanes and the configuration of the magnet system.

Observation of the thermal conductivity of warm dense tungsten plasma generated by a pulsed-power discharge using laser-induced fluorescence

To observe the transport properties of a sample of warm dense matter, we used laser-induced fluorescence to measure the thermal conductivity of tungsten plasma confined within a rigid, ruby capillary tube. We determined the density and temperature of the plasma generated by an isochoric heating device using a pulsed-power discharge. The density was determined by the initial diameter of the tungsten wire used, and the temperature was obtained by spectroscopic measurements. The temperature of the ruby capillary was obtained from its fluorescence intensity, which depends on the temperature of the outer wall. We found the thermal conductivity to be approximately 30 W/K m, thus demonstrating that the thermal conductivity of warm dense matter states can be directly evaluated using the proposed method.

Ablation plasma transport using multicusp magnetic field for laser ion source

We propose a plasma guiding method using multicusp magnetic field to transport the ablation plasma keeping the density for developing laser ion sources. To investigate the effect of guiding using the magnetic field on the ablation plasma, we demonstrated the transport of the laser ablation plasma in the multicusp magnetic field. The magnetic field was formed with eight permanent magnets and arranged to limit the plasma expansion in the radial direction. We investigated the variation of the plasma ion current density and charge distribution during transport in the magnetic field. The results indicate that the plasma is confined in the radial direction during the transport in the multicusp magnetic field.

Evaluation Method for Thermal Conductivity in Warm Dense Matter by using Ruby Fluorescence Probe

We have proposed a concept of experimentally estimating thermal conductivity in warm dense matter from the ruby fluorescence. To reduce the dimension of the system, a cylindrically arranged sample tamped by the ruby capillary has been considered. From the estimated ruby temperature, in which is simulated by the time-dependent thermal diffusion in equation, the ruby fluorescence can be obtained from 0.5 mm to 0.6 mm. The results indicated that the low density regime as ρ/ρs < 0.004 is possible to evaluate the ruby fluorescence.

Impedance control using electron beam diode in intense pulsed-power generator

To control an input energy for a load, an impedance control with a gap distance of an electron beam diode was studied using an intense pulsed-power generator. The output current of the pulsed-power generator as a function of the gap distance of electron beam diode was measured. It indicated that the behaviors of the experimentally obtained peak current and the theoretically obtained space-charge limited current were found to decrease with an increase in the gap distance. The input energy for the load was estimated from the output current, which decreased with an increase in the gap distance. It also revealed the space-charge limited current suppresses the input energy for the load with a decade.

Laboratory Scale Experiments for Collisionless Shock Generated by Taper-Cone-Shaped Plasma Focus Device

To understand the behavior of astrophysical phenomena, laboratory scale experiments with well-defined behaviors are required. Collisionless shock phenomena have unclear mechanism such as energy dissipation process and generation of highly energetic particles. To generate the collisionless shock in the laboratory scale experiments, Drake, et al. [1] has considered the required conditions, which depend on the magnetic flux density and the shock velocity. To obtain the collisionless shock, the hypersonic plasma flow generated by a taper-cone-shaped plasma focus device is proposed to evaluate in these shocks.

Target design for high energy density physics experiment using intense ion beams

A new approach for high energy density physics experiments using intense ion beams is presented. To make dense matter plasma as the interior of Jupiter, we use a diamond anvil cell for isentropic compression and the intense ion beams for isochoric heating. Results indicated that the temperature of 10ρs (ρs: solid density) pre-compressed target can be achieved 4000 K irradiated by argon ion beams. We also investigated a radiation hydrodynamics (RH) target for understanding optical properties. Making well-defined RH plasma, we calculated the spherical target using intense ion beams. The results indicated that the spherical target plasma could be point-spot like temperature distribution and target size was about 0.4 mm full width of half maximum.

HIGH EFFICIENCY CLOSED CYCLE MHD POWER GENERATION SYSTEM FOR D-T ICF REACTOR

In this study we used Inertial Confinement Fusion (ICJ?) reactor as energy source and then we examined the efficiency of power generation system using this ICF reactor. We considered an MHD generator, a gas turbine generator, a steam turbine generator and components to combine and made various power generation systems. Four kinds of power generation systems were examined and when output gas temperature was 2000K an MHD single power generation system had the highest plant efficiency of 61%, which was higher than that of a conventional turbine generation system. Temperature input to an ICF reactor was limited because of a blanket limit temperature. As a result output temperature from reactor was also affected, and this leads to affect to the plant efficiency. Generally, the higher blanket limit temperature could provide the higher efficiencies. However, when the react or output temperature was too high, the generation efficiency and the total plant efficiency decreased. Because the blanket temperature was limited to avoid the blanket being damaged, gas temperature retumed to the inlet of reactor must be low. As a resul t, some part of heat had to be released at a gas Cooler to keep the blanket temperature under