SHORT-PULSE HIGH-INTENSITY LASER-GENERATED FAST-ELECTRON TRANSPORT INTO THICK SOLID TARGETS

The transport of fast electrons generated by 1 ps, 1 mu m wavelength l aser pulses focused to spot diameters of 20 mu m and peak intensities of up to 2x10(18) W cm(-2) on to solid aluminum targets is considered using a relativistic Fokker-Planck equation, which is solved by reduci ng it to an equivalent system of stochastic differential equations. Th e background is represented by E=eta j(b), where eta is the resistivit y and j(b) is the background current density. Collisions, electric and magnetic fields, and changes in resistivity due to heating of the bac kground are included. Rotational symmetry is assumed. The treatment is valid for fast electron number densities much less than that of the b ackground, fast electron energies much greater than the background tem perature, and time scales short enough that magnetic diffusion and the rmal conduction are negligible. The neglect of ionization also limits the validity of the model. The intensities at which electric and magne tic fields become important are evaluated. The electric field lowers t he energy of fast electrons penetrating the target. The magnetic field reduces the radial spread, increases the penetration of intermediate energy fast electrons, and reflects lower energy fast electrons. Chang es in resistivity significantly affect the field generation. The impli cations for K alpha emission diagnostics are discussed.