[en] This manuscript provides a theoretical description, sometimes illustrated by experimental results, of several examples of field-matter interaction in various domains of physics, showing how the same basic concepts and theoretical methods may be used in very different physics situations. The issues addressed here are nonlinear field-matter interaction in plasma physics within the framework of classical mechanics (with a particular emphasis on wave-particle interaction), the linear analysis of beam-plasma instabilities in the relativistic regime, and the quantum description of laser-atom interaction, including quantum electrodynamics. Novel methods are systematically introduced in order to solve some very old problems, like the nonlinear counterpart of the Landau damping rate in plasma physics, for example. Moreover, our results directly apply to inertial confinement fusion, laser propagation in an atomic vapor, ion acceleration in a magnetized plasma and the physics of the Reversed Field Pinch for magnetic fusion. (author)

[en] The simplest example of a RFP-like equilibrium is introduced. It corresponds to a kinking current-carrying wire inside of a magnetic flux conserving cylinder. It suggests a scenario for dynamo in the RFP, where dynamo is a birth and death process of current filaments carrying them from the center to the edge of the plasma. This scenario and the wire model are consistent with several experimental and numerical results. The existence of reconnection events, expected from the scenario and seen in numerical simulations, is shown to support the two basic assumptions of Taylor theory of relaxation. (orig.)

[en] A new phenomenon of coherent acceleration of ions by a discrete spectrum of electrostatic waves propagating perpendicularly to a uniform magnetic field is described. It allows the energization of ions whose initial energies correspond to a region of phase space that is below the chaotic domain. The ion orbits below the chaotic domain are described very accurately using a perturbation analysis to second order in the wave amplitudes. This analysis shows that the coherent acceleration takes place only when the wave spectrum contains at least two waves whose frequencies are separated by an amount close to an integer multiple of the cyclotron frequency. The way the ion energization depends on the wave numbers and wave amplitudes is also presented in detail using the results of the perturbation analysis. copyright 1998 American Institute of Physics

[en] In this paper, we present our nonlinear kinetic modeling of stimulated Raman scattering (SRS) by the means of envelope equations, whose coefficients have been derived using a mixture of perturbative and adiabatic calculations. First examples of the numerical resolution of these envelope equations in a two-dimensional homogeneous plasma are given, and the results are compared against those of particle-in-cell (PIC) simulations. These preliminary comparisons are encouraging since our envelope code provides threshold intensities consistent with those of PIC simulations while requiring computational resources reduced by 4 to 5 orders of magnitude compared to full-kinetic codes. (authors)

[en] The stationary ray tracing method, commonly used in hydrodynamic codes to describe the laser propagation and energy deposition, is reformulated to include energy exchanges between laser beams, referred to as cross-beam energy transfer (CBET), as well as laser beam backscatterings from acoustic (Brillouin) and electron (Raman) plasma waves. These energy exchanges and scatterings are described by a Monte Carlo method simulating the creation/annihilation of rays. The algorithm has been validated against other numerical solvers and, in the case of CBET, by means of kinetic simulations. The method is efficient and can be easily implemented in already existing ray tracing packages used in many hydrodynamic codes. It can be further extended to describe other kinds of wave mixing processes such as side-scatterings and collective scatterings. (authors)

[en] In this article, we provide a theoretical description and calculate the nonlinear frequency shift, group velocity, and collisionless damping rate, ν, of a driven electron plasma wave (EPW). All these quantities, whose physical content will be discussed, are identified as terms of an envelope equation allowing one to predict how efficiently an EPW may be externally driven. This envelope equation is derived directly from Gauss' law and from the investigation of the nonlinear electron motion, provided that the time and space rates of variation of the EPW amplitude, E_p, are small compared to the plasma frequency or the inverse of the Debye length. ν arises within the EPW envelope equation as a more complicated operator than a plain damping rate and may only be viewed as such because ν(E_p)]/E_p remains nearly constant before abruptly dropping to zero. We provide a practical analytic formula for ν and show, without resorting to complex contour deformation, that in the limit E_p → 0, ν is nothing but the Landau damping rate. We then term. the 'nonlinear Landau damping rate' of the driven plasma wave. As for the nonlinear frequency shift of the driven EPW, it is also derived theoretically and found to assume values significantly different from previously published ones, which were obtained by assuming that the wave was freely propagating. Moreover, we find no limitation in k λ_D, k being the plasma wavenumber and λ_D the Debye length, for a solution to the dispersion relation to exist, and want to stress here the importance of specifying how an EPW is generated to discuss its properties. Our theoretical predictions are in excellent agreement with results inferred from Vlasov simulations of stimulated Raman scattering (SRS), and an application of our theory to the study of SRS is presented. (authors)

[en] In the typical conditions of density and electronic temperature of the Laser Megajoule (LMJ), a quantitative assessment of the Raman reflectivity requires an accurate calculation of the non-linear movement of each electron submitted to the waves propagating in the plasma. The interaction of a laser beam with a plasma generates an electronic wave shifted in frequency (that can be back-scattered) and an electron plasma wave (OPE). The OPE can give to the electrons a strongly non-linear movement by trapping them in a potential well. This non-linearity of microscopic origin has an impact on the plasma electronic density. We have succeeded in computing this plasma electronic density in a very accurate way by combining the principles of a perturbative approach with those of an adiabatic theory. Results show that the Raman diffusion can grow on temperature and density ranges more important than expected. We have predicted the threshold and the behavior of the Raman diffusion above this threshold as accurately as we had done it with a Vlasov code but by being 10000 times more rapid. (A.C.)

[en] A simplified version of the Car-Parrinello method, based on the Thomas-Fermi (local density) functional for the electrons, is adapted to the simulation of the ionic dynamics in dense plasmas. The method is illustrated by an explicit application to a degenerate one-dimensional hydrogen plasma

[en] Recent progress in experiments open a path beyond the standard paradigm that a bath of magnetic turbulence is intrinsic to the reversed field pinch (RFP): quasi single helicity (QSH) states have been found in several RFP's. This motivates a thorough theoretical study of the single helicity (SH) states of the RFP which correspond to a laminar dynamo produced by a single mode, and an integrable magnetic field with good flux surfaces, a feature favourable to good confinement. Numerical simulations of visco-resistive MHD reveal a bifurcation from SH to multiple helicity related with temporal intermittency, which is ruled by the product of resistivity by viscosity. Furthermore a mechanism of magnetic chaos healing is shown to exist when the magnetic separatrix of the dominant mode of QSH states disappears due to a saddle-node bifurcation. (author)

[en] Collisionless beam-plasma instabilities are expected to play a crucial role during the early phase of the relativistic electron transport in the Fast Ignition scheme. This Letter presents a theoretical study of these instabilities in a two-dimensional geometry, highlighting the role of unstable modes propagating obliquely to the beam direction. The main features identified through a linearized analysis in a very general kinetic framework are examined by means of a particle-in-cell simulation. Good agreement between the two approaches is observed in the linear phase. Beam trapping is found to account for the nonlinear wave saturation