Analytic theory of the linear and nonlinear behavior of the one-dimensional Brillouin and Raman scattering instabilities is given. Results are presented for the problems of an infinite homogeneous plasma and of a finite inhomogeneous plasma. Nonlinear fluid equations can predict backscatter energies the order of the incident laser energy; however, the size of the interaction region and nonlinear effects on the excited electrostatic wave are very important in determining the amount of backscatter. In many cases of contemporary interest for a high power laser incident on a target plasma, the latter effects can play a crucial role in reducing backscatter to a tolerable level.

The linear theory of electromagnetic instabilities driven by an energetic ion beam streaming parallel to a magnetic field in a homogeneous Vlasov plasma is considered. Numerical solutions of the full dispersion equation are presented. At propagation parallel to the magnetic field, there are four distinct instabilities. A sufficiently energetic beam gives rise to two unstable modes with right-hand polarization, one resonant with the beam, the other nonresonant. A beam with sufficiently large T⊥/T∥ gives rise to the left-hand ion cyclotron anisotropy instability at relatively small beam velocities, and a sufficiently hot beam drives unstable a left-hand beam resonant mode. The parametric dependences of the growth rates for the three high beam velocity instabilities are presented here. In addition, some properties at oblique propagation are examined. It is demonstrated that, as the beam drift velocity is increased, relative maxima in growth rates can arise at harmonics of the ion cyclotron resonance for both right and left elliptically polarized modes.

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General conditions under which rarefaction shocks can exist in the expanding corona of a plasma heated by a laser are derived. In particular, for the case of a two-electron temperature isothermal plasma with temperatures Th and Tc, such a shock is shown to occur if Th/Tc≳5+√24. The case of rarefaction shocks induced by the ponderomotive force is also briefly discussed.

Associated with the large heat conduction in the solar wind is a skewing of the ion and electron distribution functions. It is shown that this collisional skewing of the electron distribution function can linearly excite collisionless ion‐acoustic, electrostatic ion cyclotron, magnetoacoustic, and ion cyclotron waves in the steady‐state solar wind even though the net equilibrium current parallel to B is zero. The initial growth rates for these unstable waves are derived, and the effectiveness of the wave‐particle interactions in heating the ions and in altering the thermal and electrical conductivities is discussed.

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...

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