Plasma Motion Induced by High-Intensity Laser Heating

The macroscopic plasma response to absorption of laser radiation is examined in a one-dimensional geometry. Euler's equations with inverse bremsstrahlung energy absorption and the radiative transport equation neglecting emission and reabsorption are the governing model equations. The parameters deriving from this model are the Bouguer number, measuring the ratio of the characteristic plasma length to the absorption length at the laser frequency, and the Boltzmann number, measuring the ratio of the characteristic convective energy flux to the laser radiative energy flux. The response to incident laser radiation of an absorbing plasma slab, bounded on one side (the side from which the laser radiation impinges) by a cold, nonabsorbing gas and on the other side by a reflecting wall, is examined in detail. The initial types of plasma response are classified according to the magnitude of the Bouguer and Boltzmann numbers. For large rates of energy addition the plasma will undergo either a radiatively driven shock-wave response or a heating wave response, which is characterized by high temperatures with no induced plasma motion. An analytical solution for the heating wave and numerical solutions for each type of response are presented.