Inertial Fusion Experiments Research Articles

Light-integrating cylinder for inertial confinement fusion light balance measurements in mirror illumination systems

This report describes the design and operation of a diagnostic instrument used for light balance measurements in inertial fusion experiments. The instrument is a light-integrating cylinder that uses the integrating principles of the Ulbricht sphere, but which was designed to operate in a reflective illumination environment. The cylinder has been used to make measurements with both high-absorption disk targets and low-absorption foil targets, illuminated with 20–80 J of green (527-nm) light. We have also modeled the cylinder to determine its theoretical integrating performance under a variety of operating conditions. Initial sensitivity was measured at 0.4 V/J and degraded over target shot number to about 0.25 V/J. The instrument has a measurement accuracy of 10% for scattered light and an absorption measurement accuracy of 10% for strongly absorbing targets, and 30%–70% for weakly absorbing targets.

A hollow droplet generator for polymer shell production

Small, spherical, polymer shells are used as fuel containers in inertial fusion experiments. These shells have traditionally been made by spray drying or more recently using droplet generators. It has proven difficult to control product size and wall thickness for thermosetting materials. In this work we describe a dual orifice droplet generator for making hollow shell preforms. The inner orifice injects bubbles of a desired gas into the polymer solution droplet stream. The stream is agitated using a piezoelectric diaphragm and produces uniformly sized hollow droplets. Shells formed from these hollow preforms have tight distributions of diameter and wall thickness.

Summary Abstract: The use of poly(vinyl alcohol) shells as fuel containers for inertial fusion experiments

Summary Abstract: The use of poly(vinyl alcohol) shells as fuel containers for inertial fusion experiments

Inertial confinement fusion research at ILE Osaka

The Institute of Laser Engineering, Osaka University, has performed inertial fusion experiments using various kinds of energy drivers, such as the GEKKO series of glass lasers, the LEKKO series of CO2 lasers, and the REIDEN series of light ion beams. – As for the fuel pellet design, the well-known Cannonball target was invented to warrant a uniform compression under laser irradiation. The super-computer SX-2 was introduced to pursue the implosion physics and to optimize the pellet design. – A conceptual scheme for a laser fusion reactor was also investigated. For inertial confinement fusion reactors the SENRI series was proposed.

Adaptive stretching and rezoning as effective computational techniques for two-level paraxial Maxwell-Bloch simulation

The methods, developed in gas dynamics, which make possible the detailed calculation of the coherent interaction of short optical pulses with a nonlinear active resonant medium are presented. This paper extends earlier work by giving a rigorous and self-consistent solution of the coupled nonlinear Maxwell-Bloch equations including transverse and time-dependent phase variations. In addition, the onset of an on-resonance self-focusing and beam degradation were predicted in absorbers and in amplifiers. To accurately handle such severe energy redistribution, dynamic nonuniform computational grids were found to be necessary. The self-focusing result agrees very well with a previous perturbation treatment and with recent experiments in sodium, neon and iodine, whereas severe beam distortion, when rigorously addressing the problem of transverse boundary, was observed in high-power lasers utilized in inertial fusion experiments. The formation of dynamic self-action effects is due to the combined effects of diffraction and the inertial response of the active medium.

Shape stability for a plasma contained within a standing electromagnetic field

For an over-dense plasma located within a resonant cavity and surrounded by standing electromagnetic radiation, it is shown that shape stability depends only on the ratio of the mean plasma radius (ra) to the wavelength of the surrounding radiation. For an initial cavity mode wavenumber k10, stability occurs for k10 ra≲π. Becausetheplasma-surfaceoscillation frequency νλ is shown to scale linearly with λ (the order of the surface wave), νλ remains small compared with the electromagnetic field frequency for stable plasmas. These results are of significance in designing inertial fusion experiments in which intense electromagnetic fields are used for heating and compressing a dense plasma.