ABSTRACT
The indirect-drive scheme to inertial confinement fusion uses a large number of laser beams arranged in a symmetric angular distribution. Collective laser plasma instabilities can therefore develop that couple all the incident laser waves located in a cone to the daughter wave growing along the cone symmetry axis [D. F. DuBois et al., Phys. Fluids B 4, 241 (1992)]. With complementary diagnostics of Thomson scattering and of the scattered light, we demonstrate the occurrence of collective stimulated Brillouin sidescattering driving collective acoustic waves in indirect-drive experiments.
ABSTRACT
We present results of two-dimensional simulations of the stimulated Brillouin scattering (SBS) of an optically smoothed laser beam propagating in an expanding plasma. In the weak damping limit, both backscattered and transmitted light waves exhibit an additional spatiotemporal incoherence, which is shown to be induced by SBS taking place in an inhomogeneous plasma. This mechanism is not related to laser-beam self-focusing and is thus complementary to plasma-induced smoothing [A. J. Schmitt and B. B. Afeyan, Phys. Plasmas 5, 503 (1998)]. The incoherence induced by SBS in the entrance part of the plasma could reduce the growth of parametric instabilities developing further inside the plasma and is able to significantly enlarge the spreading angle of the transmitted light. The angular width of the backscattered light is also found to be significantly larger than the aperture angle of the incident beam.
ABSTRACT
The propagation of intense electromagnetic waves in cold magnetized plasma is tackled through a relativistic hydrodynamic approach. The analysis of coupled transverse-longitudinal plasma oscillations is performed for traveling plane waves. When these waves propagate perpendicularly to a static magnetic field, the model is describable in terms of a nonlinear dynamical system with 2 degrees of freedom. A constant of motion is obtained and the powerful classical mechanics methods can be used. A new class of solutions, i.e., the chaotic solutions, is discovered by the Poincaré surface of sections. As a result, coupled transverse-longitudinal plasma oscillations become aperiodically modulated.
ABSTRACT
In femtosecond-laser-matter interaction, collisional absorption plays an important role during the early stages of the interaction, when the laser intensity and the plasma temperature still have moderate values. We propose a cutoff impact parameter b(max) for the Coulomb logarithm lambda=ln Lambda in the electron-ion collision rate which takes into account, for an overdense plasma, the crystalline structure of the ion background. Calculations are presented for a bcc lattice and generalized to sc and fcc lattices. The results are applicable for laser intensities I(l)< or =10(17) W cm(-2) and when the Debye theory is valid, that is to say, when the Landau length is distinctly less than the minimum ion distance, and when the Debye screening is unaffected by the electron quiver motion in the laser field. We present the space angle dependence of the cutoff b(max) as also its spatial average, and we discuss the ensuing corrections to the Coulomb logarithm due to the improved values of b(max). Finally, we present the pertinent
ABSTRACT
We present a method allowing one to partly stabilize some chaotic Hamiltonians which have two degrees of freedom. The purpose of the method is to avoid the regions of V(q(1),q(2)) where its Gaussian curvature becomes negative. We show the stabilization of the Hénon-Heiles system, over a wide area, for the critical energy E=1/6. Total energy of the system varies only by a few percent.
