An ignition condition for a compressed DT sphere is studied by the use of balance relation between a heating term (alpha-particle heating) and cooling terms (expansion, radiation, and electron heat conduction). The resultant condition was compared with the model simulation carried out by Fraley et al. (1974). Effect of implosion uniformity is one of the most important elements in evaluating the laser energy required for fuel ignition. Increase of the laser energy as a function of implosion nonuniformity is shown. For a self-consistent study of implosion dynamics, a two-dimensional fluid code is developed and used for analyzing the recent high neutron yield experiment (Takabe et al. 1988). Two-dimensional fluid dynamics driven by laser irradiation nonuniformity is studied to explain the difference between the experimental result and the result of 1-D fluid simulation.

The paper presents results of an investigation of energy transport in 6-μm aluminum foils covered with a silver or gold layer irradiated with 1·06-μm, 1-ns laser-pulse at intensities 1013to 1014 W/cm2. The increase in mass ablation rate and volume heating of accelerated fragment of the foil as well as the increased range of lateral energy transport were registered. The measured plasma parameters from aluminum foils were used for testing the one-dimesional numerical code.

Efforts to demonstrate the feasibility of a gamma-ray laser scored major advances in 1987. Culminating with the successes in optically pumping the first of the 29 actual candidate isomers, priority issues were brought into better focus by the lessons learned from a wealth of new results. Perceptions were advanced so greatly that we must reassess the critical issues for 1988. Only the bottom line remains the same. A gamma-ray laser is feasible if the right combination of energy levels occurs in some real material. The likelihood of this favorable arrangement has been markedly increased by the experimental results to date.

A review of recent developments in intense ion beam diagnostics used in the international light ion inertial confinement fusion (ICF) programs will be presented. These developments have occurred in each of the several generic classes of diagnostics, namely, imaging diagnostics, particle spectrograph diagnostics, nuclear activation, and visible spectroscopy. Critical beam parameters measured by the new diagnostics include spatial profile, absolute number, species, anode plasma temperature and density, voltage, current density, and power density. A unique feature of most of these diagnostics is that they are capable of operating in hard (multi-MeV) X-ray (bremsstrahlung) backgrounds of some 109–1011 rad/s. The operating principles of each diagnostic will be summarized in the paper with examples of how the diagnostics may be integrated together to form a complete diagnostic system. The paper will close with a discussion of two new data acquisition systems that have been developed for intense beam diagnostics.

Non-perturbing high resolution spectroscopic diagnostic methods have been developed to reliably measure the temporal and spatial distributions of physical quantities in the strong-field region and in the plasmas in pulsed-power devices. The methods were employed to investigate the properties of the acceleration gap and the behavior of the highly dynamic nonequilibrium anode plasma in intense ion diodes. Conclusions on the electron density and current density in the diode gap, the magnetic field induced by the current flow, the plasma conductivity, plasma heating, plasma expansion, particle fluxes and velocity distributions in the plasma, and possible use in other pulsed-power configurations are discussed.

A theoretical model of spherical ablative implosion is presented. The implosion performances such as the target coupling efficiency are estimated from the aspect ratio and initial mass density of a target shell, provided the laser is fixed at moderate intensity for a given wavelength. The model is applied to the experimental results obtained for both plastic hollow shell targets and DT gas-filled GMB targets by use of the twelve-beam green GEKKO XII laser. In addition to the target coupling efficiency, it is shown for the gas-filled targets that the theoretical predictions of neutron yield, ion temperature, and fuel ρ and ρR are in good agreement with the experimental results. Reduction of neutron yields due to irradiation nonuniformity is also discussed, and 5% of absorption nonuniformity is found to be required for explaining the discrepancies in neutron yield between the experiments and the theory.

In this paper we present main parameters of the thermonuclear fuel and relations connecting the thickness of an isothermal homogeneous cryolayer with gaseous microballoon parameters. A model of the temperature field calculation (the azimuthal temperature gradient and the temperature distribution) and the way of shaping it under practical experimental conditions by the contact-point method is presented. The temperature distribution calculation explains the “sag” effect observed in many experiments.

A large, high density, high temperature plasma has been produced by using a high power laser with a capillary electrical discharge. The laser beam is synchronized with the discharge to reach the plasma after it emerges several hundred microns from the capillary.

Analysis is given for nonstationary propagation of rotating ion beam which has a finite length on the basis of Vlasov–Maxwell equations. The beam velocity distribution function is assumed to have a form of product of a modification function g which depends on time and axial coordinate multiplied by a steady solution fb0 which is a known function of particle velocity and radial coordinate. Unknown function g is solved as the solution of Vlasov equation through electromagnetic fields induced by leading and trailing edges. These electromagnetic fields can be solved from the Maxwell equations by using beam distribution function and motion of electrons in background plasma.

This is a short summary of research on the self-magnetically Bθ-insulated ion diode originally proposed by K. Zieher (1981, 1983, 1984, 1984a). We report the most recent progress. For detailed discussions see the forthcoming publications (Schimassek 1989; Westermann 1989). After the exploratory work of Zieher the efforts of recent years have concentrated on the numerical simulation (Westermann 1988; 1988a; 1988b), the development of detailed diagnostic tools (Rogner & Schultheiss 1986; Kühn & Rogner 1985; Klumpp & Bluhm 1986) and the focusing properties of the Bθ-diode (Citron et al. 1986; Bauer et al. 1987; Schimassek et al. 1988; Westermann 1988c). Experiments and numerical simulations on three modifications of the diode will be reported (version I, II, III).

The physics and technology for e-beam generation, large volume excitation and the ultra-violet optics for high power KrF lasers is presented. The potential, due to the charge deposition, induces a return current in the plasma which balances the e-beam current. The local equilibrium mechanism stabilizes the large volume excitation using intense electron beams. The spatial and temporal characteristics of large aperture diodes are analyzed. Substantial progress in ultra violet optics in Japan has been achieved. The damage threshold of HR dielectric coating increases up to 11 J/cm2 by using low absorption materials.

A formalism for the analysis of the Rayleigh–Taylor instability in the multi-structured solid or shell targets is presented. The formulation covers both the plane and the curved geometry targets. A generalized eigenvalue equation for the exponential growth rate of the instability is derived along with the necessary boundary conditions. Analytical solutions for the growth rate are presented for some elementary density profiles and a comparative study is made between the plane, cylindrical and spherical targets. The solution for the step function density profile is generalized for any number Nof zones forming an arbitrary density profile. This general formulation is illustrated with the explicit calculations for N = 3 and 4. A qualitative treatment of the effects of the ablative flow is also presented. This study predicts a stabilizing effect of the ablative flow on the growth of the instability. Further, a dynamic analysis of the instability growth rate is presented for a representative inertial confinement fusion spherical solid target driven by the laser beams. This study demonstrates that an approximate analysis of the instability with the time independent initial density profile gives the conservative results for the instability growth rate.

The present status of the development of a high-power KrF laser system, Ashura, is described. The main amplifier has generated 710 J (95 ns) at the pumping density of 1·lMW/cm3 with the wall plug efficiency of 2·0%. Maximum power of 9·0 GW (200 J/22 ns) per beam has been obtained from the beam lines of six-time pulse multiplexing. Power density of 1 × 1014 W/cm2 has been achieved on target with a 10−6 pre-pulse.

Light ion beams for the energy drive for inertial confinement fusion (ICF) research have been studied on a super high voltage generation system (SHVS) using an inductive voltage adder system. A simple analysis implied the capability of the output voltage of several tens of MV. This system has a feasibility of acceleration of ions heavier than proton. The two-stage charge stripping ion diode is considered a SHVS diode. This diode reduces the size of the induction adder module and extends the possible power range in operation. We have constructed a prototype SHVS, which consists of eight stages of induction cavities (4MV, 40kA, 100ns) powered by a Reiden IV pulse power machine. The first ion diode experiments on the induction adder were performed with the beam extraction type ion diode (Br applied magnetic field). The injection plasma ion source was used to control the diode impedance and then the diode voltage. The time delay of ion current turn-on was reduced from 15–20 ns to less than 5 ns by this ion source.

Use is made of the Vlasov–Maxwell equations to derive an eigenvalue equation describing the extraordinary–mode stability properties of relativistic, non-neutral electron flow in high-voltage diodes. The analysis is based on well-established theoretical techniques developed in basic studies of the kinetic equilibrium and stability properties of nonneutral plasmas characterized by intense self fields. The formal eigenvalue equation is derived for extraordinary-mode flute perturbations in a planar diode. As a specific example, perturbations are considered about the choice of self-consistent Vlasov equilibrium , where . is the electron density at the cathode (x = 0), H is the energy, and Py is the canonical momentum in the Y-direction (the direction of the equilibrium electron flow). As a limiting case, the planar eigenvalue equation is further simplified for low-frequency long-wavelength perturbations with |ω − kvd, ≪ ωυ where and and ⋯c = eB0/mc, and B0ệz is the applied magnetic field in the vacuum region xb < x ≤ d. Here, the outer edge of the electron layer is located at x = xb; ω is complex oscillation frequency; k is the wavenumber in the y-direction; ωυ is the characteristic betatron frequency for oscillations in the x′-orbit about the equilibrium value x′ = x0 = xb/2; and Vd is the average electron flow velocity in the y-direction at x = x0. In simplifying the orbit integrals, a model is adopted in which the eigenfunction approximated by , where x′(t′) is the x′-orbit in the equilibrium field configuration. A detailed analysis of the resulting eigenvalue equation for , derived for low-frequency long-wavelength perturbations, is the subject of a companion paper.

The fluid-dynamics of the corona ejected by laser-fusion targets in the direct-drive approach (thermal radiation and atomic physics unimportant) is discussed. A two-fluid model involves inverse bremsstrahlung absorption, refraction, different ion and electron temperatures with energy exchange, different ion and electron velocities and magnetic field generation, and their effect on ion-electron friction and heat flux. Four dimensionless parameters determine coronal regimes for one-dimensional flows under uniform irradiation. One additional parameter is involved in two-dimensional problems, including the stability of one-dimensional flows, and the smoothing of non-uniform driving.