Flame Propagation and Overdense Heating in a Laser Created Plasma

A one-dimensional continuum hydrodynamic theory is used to investigate the structure of the deflagration wave which occurs when a laser light beam impinges on a solid target. It is shown that the nonlinear electron heat conduction is responsible for most of the structure; a region of density higher than the cutoff is strongly heated. Density and temperature profiles are calculated. An approximate solution for the thickness x of the overdense layer gives x = 45(γ−1) / (5γ−1)(m/k)3/2A(Tc2/ρc) (m is the ion mass, k is the Boltzmann constant, A T5/2 is the nonlinear electron heat conduction coefficient, Tc is the temperature of the plasma at cutoff density ρc. The average density in the layer is about twice the cutoff density. The effects of viscosity and (since electrons are heated by the laser light) of ion-electron relaxation are evaluated.