NONLINEAR COLLISIONAL ABSORPTION IN LASER-DRIVEN PLASMAS

The collisional heating rate of a fully ionized plasma driven by a strong electromagnetic pump wave is re-examined both analytically and with two-dimensional particle-in-cell (PIC) simulations. The high frequency conductivity model of Dawson and Oberman [J. Dawson and C. Oberman, Phys. Fluids 5, 517(1962)] is extended for the case in which the quiver velocity υ0 = eE/mω0 is much larger than the thermal velocity υth and its equivalence to the results of Silin [V. P. Silin, Sov. Phys. JETP 20, 1510 (1965)] is shown. The Dawson and Oberman model is reduced to two-dimensions for comparison with the PIC simulations. Excellent agreement between the theory and the simulations for υ0/ υth≤ 1 is obtained. However, when υ0/ υth> 1 and the excursion amplitude χ0= eElmω02 is larger than the Debye length λD, the simulations show enhancements in the collision frequency from the theory. A possible mechanism for this enhancement is provided. © 1994 American Institute of Physics.