The linear stability of an ablating plasma is investigated as an eigenvalue problem by assuming the plasma to be at the stationary state. For various structures of the ablating plasma, the growth rate is found to be expressed well in the form γ=α(kg)1/2 −βkVa, where α=0.9, β≂3–4, and Va is the flow velocity across the ablation front, and is found to agree well with recent two-dimensional simulations in a classical transport regime. Short-wavelength lasers inducing enhanced mass ablation are suggested to be advantageous to stable implosion because of the ablative stabilization.

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Particle-in-cell simulation methods for doing full electromagnetic simulations of collisionless plasma phenomena are described and applied to the Weibel instability in one and two dimensions. Magnetic particle trapping and subsequent mode coalescing are seen. Magnetic field energy is seen to reach 10% of the total particle energy. The different electromagnetic simulation methods are compared.

The phenomenology of thermonuclear burn in deuterium-tritium microspheres at high densities is described, and numerical results characterizing the burn for a broad range of initial conditions are given. The fractional burnup, bootstrap-heating, and depletion of the DT fuel, its expansive disassembly, and thermonuclear ignition by propagating burn from central hot spots in the microspheres are discussed. Extensive numerical results from a 3 T Lagrangian simulation code are presented. The yields Y0 from uniform 10, 1, and 0.1 μg microspheres with densities ρ = 1 to 4 × 104 g/cm3 and temperatures Te = Ti = 1.8 to 100 keV are given. It is shown that Y0 ∼ ρR, ρR < 0.3 (R is the microsphere radius) or, equivalently, Y0 ∼ ρ2/3 for spheres of fixed mass m. The gain-factor G0 ≡ Y0/mI0 (I0 is the internal energy) is shown to measure burn efficiency in uniform microspheres. More than a four-fold increment in the gain factor is shown to derive from apportionment of the internal energy in a central hot spot. The limiting effects of electron degeneracy on the gain factor are outlined. As a guideline, the experimental observation of 1013 neutrons/kJ of input laser energy is established as proof of good absorption; 1015/kJ will imply yields exceeding break even.

A detailed theoretical and simulation study of resonant absorption in a hot plasma is presented which isolates the behavior of the plasma for times short compared to an ion response time. The extent to which an electron fluid model can describe the absorption process in the kinetic regime is discussed. At high intensities the absorbed energy is observed to be deposited in a suprathermal tail of electrons whose energy varies approximately as the square root of the incident power. The density profile modification due to the ion response to the ponderomotive force is also discussed.When an electromagnetic wave is obliquely incident on an inhomogeneous plasma and polarized in the plane of incidence, it is well known that it can be absorbed resonantly by linear mode conversion into an electron plasma wave. ' ' This process, known as resonant absorption, has important implications for laser target experiments and microwave laboratory experiments. ' Most theoretical work has been done for a cold plasma, '" ' while warm-plasma calculations have been either incomplete' or incorrect. 'For gradient lengths long compared to the wavelength of light or koL»1 (where ko is the incident free-space wave number and L is the density scale length), computer simulations in a hot plasma, with fixed ions show that the absorption coefficient is virtually unmodified from the cold-electron case. Theoretical calculations based on a fluid description which agree with these computer simulations indicate that the absorption coefficient is virtually unmodified for temperatures up to 100 keV. At low' intensities these theoretical calculations predict the field structures seen in simulations, while at high intensities a nonlinear dissipation must be added to obtain agreement. This nonlinear dissipation is required at high intensities to account for the acceleration towards the low-density region of the plasma of a small number of electrons to very high energies. To describe resonant absorption in a hot plasma, we combine the linearized electron-momentum equation with Maxwell's equations. An adiabatic pressure law is assumed for the high-frequency electron motion, ion motion is neglected, and the fields are assumed to vary as e' '. V~E = 4~en"V x E = i (~/c) B-, VxB =(4n/c)7 -(i~/c) E, e'in, E ieT, Vn" J= . + yVn -n m(tvvv'v) m(tvviv ) ' ' v, )'where n, is the background plasma density; T, , m, and e are the electron's temperature, mass, and charge, respectively; c is the velocity of light; and y is the usual ratio of specific heats and is chosen equal to 3. In factoring the damping in the electron-momentum equation a different damping rate appears in the electric field term than in the electron pressure term. The significance of this phenomenological damping is discussed below. Combining these equations we obtain the general steady-state wave equation for E:where~~=47)noe'/m. ln particular, we consider the case of a slab of plasma with no =no(x) only and the electromagnetic wave obliquely incident on this slab, with the electric field polarized i...