Osamu Komeda

Multilayered polycrystallization in single-crystal YSZ by laser-shock compression

A single shot of an ultra-intense laser with 0.8 J of energy and a pulse width of 110 fs (peak intensity of W cm−2) is divided into two beams and the two beams counter-irradiated onto a 0.5 mm-thick single crystal yttria-stabilized zirconia (YSZ), changing the YSZ into a multilayered polycrystalline state. The laser-driven shock wave of the intensity 7.6 Pa penetrated the crystal as deep as 96 m, causing formation of a four-layered structure (the first layer from the surface to 12 m, the second from 12 to 28 m, the third from 28 to 96 m, and the fourth from 96 to 130 m, respectively). The grain size of the first layer was 1 m, while that of the second layer was broken into a few tens nanometers. The grain size of the third layer was a few hundred nanometers to a few ten micrometers. The area deeper than 96 m remained as a single crystal. The plasma heat wave might remelt the first layer, resulting in the grain size becoming larger than that of the second layer. The surface polycrystallization seems to maintain the residual stresses frozen in the film thickness direction. Our experimentally observed spatial profile of the grain size can be explained by this shock and heat waves model.

Neutron Generator Using Spherical Targets on a Rotating Disk Irradiated with an Ultraintense Laser at 1.25 Hz

Abstract A neutron generator is developed using 1-mm-diam spherical deuterated polystyrene targets on a rotating disk irradiated with an ultrahigh-intensity (>1018 W/cm2) diode-pumped laser. It consists of a rotating disk supplier, the targets, and a control system to irradiate the targets at 1.25 Hz. We adjusted the laser focus and position on the target to obtain the maximum neutron yield.

1-Hz Bead-Pellet Injection System for Fusion Reaction Engaged by a Laser HAMA Using Ultra-Intense Counter Beams

Abstract The injection and engagement of pellets using laser beam irradiation is one of the key technologies to realize a laser-driven inertial fusion energy (IFE) reactor. We irradiated ultra-intense laser (11 TW: 0.6 J/110 fs 2 beams with a focal intensity of 510 W/cm) in counter configuration on flying 1-mm-diameter deuterated polystyrene beads beyond 600 pellets on an average at 1 Hz and 10 min per cycle for 4 years. An injection system delivers pellets with free-fall that consists of a header for pellet delivery by disk rotation and a detection unit for synchronizing the motion of a pellet for laser engagement in time. During laser irradiation, the free-falling pellet placement was at Δx = 1 mm, Δy = 0.4 mm on a plane perpendicular to the falling direction, and Δz = 0.1 mm in the falling direction at the moment of laser irradiation. Using a two-directional probe shadowgraph system, we succeeded in aligning the pellet-falling position with a laser engagement probability greater than 70%; the probability improved from the previous experiments wherein the probabilities were less than 20%. As a result, the shot probability is 27% for gamma-ray generation resulting from ultra-intense laser-matter interactions and 22% for detection of signals corresponding to fusion neutrons with a maximum yield of 4 10 n/shot. The neutron reaction induced from an integrated system of pellet injector and laser is a decisive step in the research and development of an IFE reactor.

Target Monitoring and Plasma Diagnosis using 2ω probe beam for CANDY

We have developed the shadowgraph and interferometer with second-harmonic of heating pulses laser to observe target and plasma in highly-repetitive fusion reaction experiments. In the deuterated polystyrene ((C8D8)n double foil experiment, we confirm implosion plasma and plasma collision. In target injection experiment at a 1 Hz rate, we measure the position of the flying deuterated polystyrene beads at the moment of laser pulse illumination and observe the plasma generation by counter-illumination by 0.63 J, 800 nm, and 104 fs laser pulses.

Progress toward a unified kJ-machine CANDY

To construct a unified experimental machine CANDY using a kJ DPSSL driver in the fast-ignition scheme, the Laser for Fast Ignition Experiment (LFEX) at Osaka is used, showing that the laser-driven ions heat the preimploded core of a deuterated polystyrene (CD) shell target from 0.8 keV to 2 keV, resulting in 5 x 108 DD neutrons best ever obtained in the scheme. 4-J/10-Hz DPSSL laser HAMA is for the first time applied to the CD shell implosion- core heating experiments in the fast ignition scheme to yield neutrons and also to a continuous target injection, which yields neutrons of 3 x 105 n/4πsr n/shot.

Amorphous nanostructuralization in HOPG by 1014 W cm-2 laser

This reports provide an amorphous nanostructuralization technique on the surface modification in Highly Oriented Pyrolytic Graphite (HOPG) by using a femtosecond laser. We showed, for the first time, that the surface of HOPG is changed to the amorphous nanostructuralization graphite by using a femtosecond laser-driven compression technique. Our results also suggest that the HOPG surface is changed until the deeper area from the surface by the laser-driven shock wave. A single shot of a femtosecond laser beam (1.27 ~ 1.33×1014 Wcm~2 in intensity, with 2 mm-diameter, and 110 fs in pulse width) is irradiated under the vacuum ambience onto a 2 mm-thick of HOPG. The calculated impact pressures on a sample was 8.3 ~ 8.7 GPa. Crystal structure in the HOPG were analyzed using a Raman spectroscopy and an X-ray diffraction, those analyzing depth from the surface were 50 nm and 350 μm, respectively.

Upgrade of repetitive fast-heating fusion driver HAMA to implode a shell target by using diode pumped solid state laser

The HAMA is 1-Hz fast heating fusion driver pumped by a 10 J second-harmonic of diode-pumped Nd:glass laser: KURE-1. We have upgraded HAMA to realize an implosion of spherical shell target by using a remaining fundamental beam from KURE-1. This beam of 6 J/1 Hz is transported to the current counter irradiation system. The resulting beam includes three pulses in sequence: 2.2 J/15 ns and 0.7 J/300 ps for implosion, and 0.5 J/ 190 fs for heating. We estimate the implosion dynamics from 1-D radiation hydrodynamic code (START- 1D). It indicates a possibility of tailored-pulse implosion by optimizing the beam spot sizes of imploding beams on the target surface. This upgrade leads to a demonstration of repetitive implosion and additional heating of a spherical shell target in accordance with a repetition of laser operation and that of a target injection system.

Repetitive Solid Spherical Pellet Injection and Irradiation toward the Repetitive-mode Fast-Ignition Fusion miniReactor CANDY.

Pellet injection and repetitive laser illumination are key technologies for realizing inertial fusion energy[1-4]. Neutron generator using lasers also requires a repeating pellet target supplier. Here we present the first demonstration of target injection and neutron generation[5]. We injected more than 1300 spherical deuterated polystyrene(C8D8) bead pellet targets during 23 minutes at 1 Hz(Fig. 1). After the pellet targets fell for a distance of 18 cm, we applied the synchronized laser-diode-pumped ultra-intense laser HAMA. The laser intensity at the focal point is 5 x 1018 W/cm2, which is high enough to generate neutrons. As a result of the irradiation, we produced 2.45-MeV DD neutrons. Figure 2 shows the neutron time-of-flight signals detected by plastic scintillators coupled to photomultipliers. The neutron energy was calculated by the time-of-flight method. The maximum neutron yield was 9.5 x 104/4π sr. The result is a step toward fusion power and also suggests possible industrial neutron sources.

A study on potential applicability of superconducting material to next generation vehicles

Abstract 1. 1. SC energy storage devices and SC motor were applied to a vehicle with ultra low temperature liquid fuel. The vehicle using new SC system called SC Motor Coil System will exceed total energy efficiency of gasoline powered vehicles. 2. 2. High performance SC wire is needed to achieve good energy efficiency. We also indicated that SC magnetic field-shield film can improve total energy efficiency by reducing SC Coil weight.