Collisionless plasma expansion and fast ion generation at plasma-vacuum boundary

Collisionless plasma expansion into a vacuum is investigated by computational treatment of a system of Vlasov equations for both ions and electrons coupled by a selfconsistent field. High-velocity low-density mass expansion is observed as a result of an electrostatic acceleration of ions.     

Relaxation of fast electrons in laser fusion targets

Collisional relaxation of a low density beam of non-thermal electrons injected into a high density Maxwellian plasma is investigated by computational treatment of Fokker-Planck type equation, with respect to the fast electron energy deposition and geometry configuration effects.     

Self-similar model of laser-induced plasma expansion affected by radiation pressure

In a stage of evolved gasdynamics a self-similar solution of laser plasma isothermal expansion including radiation pressure has been found and discussed with respect to D and D + shock profiles time evolution.     

Absorption and reflection of laser produced plasma with spherical symmetry

The consistent system of hydrodynamical and Maxwell equations is solved numerically to simulate the absorption and reflection of a laser light by a spherical target. Both inverse bremsstrahlung and anomalous absorption mechanisms are included.     

Collisionless limit of resonance absorption

It has been shown that transition from warm to cold ( _ef =0) or from collisional to collisionless (=0) plasma solutions of Maxwell's equations for resonance at oblique incidence has to be proceeded carefully, not to violate the continuity of transverse field components at the cut-off. Coefficient of reflsxivity becomesR=1 for collisionless cold plasma, instead ofR<1 usually obtained, as a consequence of formal limit of warm or collisional solutions to the cold or collisionless ones.On leave of absence fromTechnical University of Prague, Department of Physical Electronics, Behová 7, 115 19 Praha 1, Czechoslovakia.     

Some electromagnetic resonant properties of laser-induced plasmas

Resonant electromagnetic properties of plasma density profiles modified by ponderomotive force and found in analytical works and numerical calculations are investigated from the aspect of reflectivity and profile stability to the spatial variations of the feedback ponderomotive force.     

Theoretical model for the wetting of a rough surface

Many applications would benefit from an understanding of the physical mechanism behind fluid movement on rough surfaces, including the movement of water or contaminants within an unsaturated rock fracture. Presented is a theoretical investigation of the effect of surface roughness on fluid spreading. It is known that surface roughness enhances the effects of hydrophobic or hydrophilic behavior, as well as allowing for faster spreading of a hydrophilic fluid. A model is presented based on the classification of the regimes of spreading that occur when fluid encounters a rough surface: microscopic precursor film, mesoscopic invasion of roughness and macroscopic reaction to external forces. A theoretical relationship is developed for the physical mechanisms that drive mesoscopic invasion, which is used to guide a discussion of the implications of the theory on spreading conditions. Development of the analytical equation is based on a balance between capillary forces and frictional resistive forces. Chemical heterogeneity is ignored. The effect of various methods for estimating viscous dissipation is compared to available data from fluid rise on roughness experiments. Methods that account more accurately for roughness shape better explain the data as they account for more surface friction; the best fit was found for a hydraulic diameter approximation. The analytical solution implies the existence of a critical contact angle that is a function of roughness geometry, below which fluid will spread and above which fluid will resist spreading. The resulting equation predicts movement of a liquid invasion front with a square root of time dependence, mathematically resembling a diffusive process.