Laser Fusion Research Research Articles

Recent laser fusion research activities of ILE, Osaka University

Reviewed are the recent laser fusion research activities of ILE, Osaka University. The issues which are discussed here are: (i) the present status of the GEKKO XII laser system; (ii) recent achievements on implosion hydrodynamics; (iii) implosion stability and symmetry in GEKKO XII experiments; and (iv) fundamental research related to fast ignitors. One of the important recent achievements is the finding of reduction of the Rayleigh–Taylor growth rate due to the non-local heat transport in directly-driven ablation plasmas. Another significant progress is the observation and analysis of the intense laser channeling in over-dense plasmas. Those two achievements are described in detail.

Ultrafast two-dimensional x-ray imaging with x-ray streak cameras for laser fusion research (invited)

Ultrafast two-dimensional x-ray imaging is required for diagnosing laser-driven inertial confinement fusion plasmas. Image sampling technique with x-ray streak cameras can meet this requirement. Multi-imaging x-ray streak camera method (MIXS) with temporal and spatial resolutions of 10 ps and 15 μm, respectively, has been developed and successfully utilized for diagnosing the uniformity and heating process of the imploded core plasmas. The two-dimensional sampling-image x-ray streak camera method is also presented. Two types of spectroscopic applications of the MIXS have been developed recently. One is multichannel MIXS, which has three MIXS channels with various spectral responses for time-resolved two-dimensional temperature measurement of the plasmas. Another is monochromatic MIXS for temperature, density, and mixing measurement, in which monochromatic images with Bragg crystals are coupled to MIXS.

Laser Fusion Research at Ile Osaka University

The progress of laser fusion research at the Institute of Laser Engineering, Osaka University is reviewed. They are physics investigations on target implosion, development of laser technologies, and R&D for laser fusion power plants. The long term strategy of Inertial Fusion Energy (IFE) development has been reexamined taking into account the recent progress of implosion physics and reactor related technologies. 15 refs., 12 figs.

Ultra-fast 2-dimensional X-ray imaging with a 10-ps resolution for use in laser fusion research

2-dimensional x-ray imaging of the laser fusion target is now possible with 10-ps temporal resolution by using recently developed multi-imaging x-ray streak (MIXS) technique. Structures in the x-ray image of the laser-imploded core, symmetry and size, were found to be rapidly changing with 10-ps time scale.

Recent progress in laser fusion research at Osaka University: Uniformity and stability issues*

Improvement of laser irradiation uniformity in the Gekko XII system [IEEE J. Quantum Electron. QE-17, 1639 (1981)], both single beam pattern and power balance, is discussed. Substantial reduction of laser absorption nonuniformity is obtained for spherical harmonic modes greater than 15 by introducing spectrally dispersed amplified spontaneous emission. No perturbation growth is observed in flat foils accelerated by spectrally dispersed amplified spontaneous emission. Dependences of laser absorption uniformity on beam pattern and power imbalance are investigated in detail. The design goal of the power imbalance in the precision Gekko XII system is 3% in peak to valley, and laser absorption nonuniformity is estimated to be a few percent. Growth of hydrodynamic instabilities is analyzed for high convergence ratio implosions in the precision Gekko XII system.

Production of very large, sub-tenth-critical plasmas for laser-fusion research

The development of a plasma environment that is appropriate for the study of low-gain processes in laser-fusion plasmas is reported. These plasmas have long scale lengths, low densities, and no quarter-critical or critical-density surfaces. The plasmas were created by two-sided irradiation of CH foils with 15 kJ of 351 nm laser light. When the peak electron density in the plasma had decayed to about 2×1020 cm−3, the parabolic density profile was estimated to have a full width at half-maximum of 3 mm and the electron temperature was estimated to be 1 keV. Probe lasers of different wavelengths were used to measure the peak electron density via stimulated scattering processes and odd half-harmonic generation. Sufficiently accurate modeling of the laser-irradiation conditions led to improved agreement between the experiment and two-dimensional (2-D) computer simulations.

A distributed control and monitor system used in laser fusion research

Laser fusion research experiments require very low pressure environments to properly diagnose the plasma physics phenomena occurring during laser fusion reactions. Target chambers with very large and complex pumping systems are required to achieve and maintain these extremely low pressures. This paper describes a recently installed distributed control and monitoring system that automates the operation of these pumping systems. Through automation, this system is providing an enhanced shot rate by reducing the manpower required to ready the system for a target shot while increasing the overall safety of the system.

High power laser system ISKRA V

The 12-beam, photodisssociative iodine laser system ISKRA V has been built for laser fusion research. In this article we describe the optical scheme, elements and parameters of the output radiation. Pulse power of 100 TW was achieved in the preliminary experiments.

Plasma Density Fluctuations and the Physics of Short-pulse Laser-produced Plasmas

Abstract Laser-produced plasmas are studied for their relevance to laser fusion research, as bright pulsed sources of X-rays and fast particles, as well as for the fundamental plasma physics processes they reveal. The programme on laser-plasma-interaction physics at the Australian National University has gained prominence for elucidating the physics of plasmas generated using short laser pulses at very high intensity where complex nonlinear processes dominate behaviour. This review will discuss some of the results from that programme and in particular relate many of the observed phenomena to the existence of density fluctuations in the plasma.

Diagnostic complex for investigations of laser fusion physical processes

The key physical processes of the laser fusion are well known and include the laser beam absorption, the heat transfer from the absorption zone to the ablation surface, the shell ablation acceleration and fusion fuel compression, the initiation of an effective thermonuclear burn. The first and second issues are investigated in detail on the small and moderate size facilities and high level of understanding is achieved on both phenomena. On the other hand, to study the thermonuclear burn seriously the large scale experiments should be carried out on the facilities of the next generation. Thus the efficiency and stability of the shell acceleration are today the main objects of experimental investigations in the majority of the laser fusion research laboratories. This paper is devoted to the development of the diagnostic methods just for studies of these problems.

I n s i t u measurement of micromass of the fuel in a cryogenic foam target for laser fusion research

We have presented a novel in situ method which is simple and sensitive, to measure the micromass of the fuel layer in a cryogenic foam target. In this method, a foam shell is mounted on a flexible polyester fiber 7 μm in diameter and 800 μm in length. The fiber is suspended with a stalk which is mechanically vibrated at any given frequency. The resonant frequency of the elastic vibration of a foam-fiber system is measured before and after fuel loading. The mass of the fuel can be determined from the change in the resonance frequency in the range from submicrograms to submilligrams. The resolution of this system, which is limited by the Q factor of the foam-fiber system, is better than 0.2 μg corresponding to the measurement accuracy of 0.1%.

Design of a normal incidence multilayer imaging X-ray microscope

Normal incidence multilayer Cassegrain x-ray telescopes were flown on the Stanford/ MSFC Rocket X-Ray Spectroheliograph. These instruments produced high spatial resolution images of the Sun and conclusively demonstrated that doubly reflecting multilayer x-ray optical systems are feasible. The images indicated that aplanatic imaging soft x-ray/EUV microscopes should be achievable using multilayer optics technology. We have designed a doubly reflecting normal incidence multilayer imaging x-ray microscope based on the Schwarzschild configuration. The Schwarzschild microscope utilizes two spherical mirrors with concentric radii of curvature which are chosen such that the third-order spherical aberration and coma are minimized. We discuss the design of the microscope and the results of the optical system ray trace analysis which indicates that diffraction-limited performance with 600 Å spatial resolution should be obtainable over a 1 mm field of view at a wavelength of 100 Å. Fabrication of several imaging soft x-ray microscopes based upon these designs, for use in conjunction with x-ray telescopes and laser fusion research, is now in progress. High resolution aplanatic imaging x-ray microscopes using normal incidence multilayer x-ray mirrors should have many important applications in advanced x-ray astronomical instrumentation, x-ray lithography, biological, biomedical, metallurgical, and laser fusion research.

Shifts in atomic understanding

Technology is set to yield, in the near future, unprecedentedly short (1-14 S) and intense (1017–1019W cm-2) light pulses. Such intensities have in the past been the preserve of the gigantic systems associated with laser fusion research but a considerable reduction in system size has made them available to the atomic physicist. Experiments using such lasers are just beginning and there have been as yet few investigations at intensities beyond 1014 W cm-2. Nevertheless these have already provided some delightful surprises.

Laser fusion experiment

The recent progress of laser fusion research has been remarkable in obtaining the high density of more than 100 times solid density (Nakai et al. 1988) and high temperature plasma producing thermonuclear neutrons of 1013 per shot (pellet gain of 0·2%) (Yamanaka et al. 1986a) and in the understanding of the implosion physics. The data bases of the laser fusion are rapidly being accumulated and the technologies for the advanced experiments have been developed, both of which enable us to proceed toward the fusion ignition experiment and the achievement of the breakeven conditions.

Target fabrication for laser fusion research in Japan

A review of target fabrication for laser fusion research in Japan conducted at the Institute of Laser Engineering, Osaka University, the Department of Electrical Engineering, Kinki University, and the Department of Electrical Engineering, Gifu University is presented. An emulsion technique is employed to manufacture polymer spheres. Excimer laser irradiation on polystyrene shells reduces permeation of hydrogen. Irradiation of UV radiation from a Hg lamp is revealed to be useful in making CHDT shells enhancing tritium exchange rate. A polymer coating on a levitated target is achieved by excimer-laser-induced chemical vapor deposition. A new immersing and heating technique has been developed to make a cryogenic foam target. Nondestructive fuel assay for the cryogenic foam target has been made by means of β-ray attenuation. A magnetic levitation technique for laser irradiation of a support-free target is introduced.

Design of a Normal Incidence Multilayer Imaging X-Ray Microscope

Normal incidence multilayer Cassegrain x-ray telescopes were flown on the Stanford/MSFC Rocket X-Ray Spectroheliograph. These instruments produced high spatial resolution images of the Sun and conclusively demonstrated that doubly reflecting multilayer x-ray optical systems are feasible. The images indicated that aplanatic imaging soft x-ray /EUV microscopes should be achievable using multilayer optics technology. We have designed a doubly reflecting normal incidence multilayer imaging x-ray microscope based on the Schwarzschild configuration. The Schwarzschild microscope utilizes two spherical mirrors with concentric radii of curvature which are chosen such that the third-order spherical aberration and coma are minimized. We discuss the design of the microscope and the results of the optical system ray trace analysis which indicates that diffraction-limited performance with 600 Å spatial resolution should be obtainable over a 1 mm field of view at a wavelength of 100 Å. Fabrication of several imaging soft x-ray microscopes based upon these designs, for use in conjunction with x-ray telescopes and laser fusion research, is now in progress. High resolution aplanatic imaging x-ray microscopes using normal incidence multilayer x-ray mirrors should have many important applications in advanced x-ray astronomical instrumentation, x-ray lithography, biological, biomedical, metallurgical, and laser fusion research.

Inertial fusion program in Japan and ignition experiment facility by laser

The recent progress in laser fusion research is remarkable with respect to obtaining the high density and high temperature plasma which produces thermonuclear neutrons of 10 13 per shot (pellet gain of 0.2%) and to the understanding of implosion physics. Data bases for laser fusion have been accumulated and technologies for advanced experiments have been developed, both of which enable us to make the research step toward the fusion ignition experiment and the achievement of the breakeven condition, which is estimated to be possible with a 100 kJ blue laser. The demonstration of high gain pellets requires laser energy in the range MJ in blue light. The design studies of the MJ laser are continue in the framework of the solid state laser at ILE. The design studies on the commercial reactor of ICF have proceeded and several conceptual designs have been proposed. These designs utilize a liquid metal first wall and blanket which enable long life for commercial use. As a consequence, the ICF reactor has technically a high feasibility for commercial application.

特集―レーザ核融合と精密工学／展望 ヨーロッパにおけるレーザ核融合研究 現代工学への挑戦

特集―レーザ核融合と精密工学／展望 ヨーロッパにおけるレーザ核融合研究 現代工学への挑戦

Progress of laser fusion research with GEKKO XII glass laser and KONGHO project for breakeven.

The progress of laser fusion research is remarkable in obtaining the high density (100 times solid density) and high temperature plasma and in the understanding of the implosion physics. Thermonuclear neutrons of 1013 per shot and pellet gain of 0.2% have been achieved. The data bases of the laser fusion have been accumulated for the fusion ignition experiment and the achievement of the breakeven condition is estimated to be possible with 100 kJ blue laser.

Progress of Laser Fusion Research with GEKKO XII Glass Laser and KONGHO Project for Breakeven

The progress of laser fusion research is remarkable in obtaining the high density (100 times solid density) and high temperature plasma and in the understanding of the implosion physics. Thermonuclear neutrons of 1013 per shot and pellet gain of 0.2% have been achieved. The data bases of the laser fusion have been accumulated for the fusion ignition experiment and the achievement of the breakeven condition is estimated to be possible with 100 kJ blue laser.