Plasma electron kinetics in a weak high-frequency field and magnetic field amplification

We describe the linear stage of Weibel instability in a plasma heated via inverse bremsstrahlung absorption of a high-frequency, moderate intensity radiation field under conditions in which the plasma electron velocity distribution function is weakly anisotropic. We report on the possibility of a significant amplification of spontaneous magnetic fields both in the case of an electron distribution function slightly departing from a Maxwellian in the region of subthermal velocities, and in the case where the Langdon nonequilibrium distribution is formed. We show that the direct influence of collisions on the Weibel instability growth rate may be traced back to subthermal electrons, for which the effective collision frequency is large.