LANGEVIN APPROACH TO COLLISIONAL BREMSSTRAHLUNG IN A MAGNETIC-FIELD

Using the appropriate Langevin equations describing the stochastic mot ion of test electrons, we investigate the problem of the changes of ki netic energy and velocity distribution of electrons colliding with ion s in the presence of a moderately strong radiation field and a steady, homogeneous magnetic field B. The cases where the electric field of t he wave is either linearly polarized along B, or left- or right-hand c ircularly polarized on a plane perpendicular to B, are explicitly cons idered. The results concerning the kinetic-energy changes extend simil ar results obtained by the same authors using a different approach. Th e results concerning the changes of the velocity distribution may be s ummarized as follows. For a linearly polarized wave, collisional brems strahlung forces the slow absorbing electrons and all emitting electro ns to align on average their velocities along the electric-field direc tion. Velocity randomization due to pure collisions mostly contrasts t his process, and is dominant for fast electrons. For circularly polari zed radiation, the electrons are forced by collisional bremsstrahlung to draw their velocity near to the polarization plane if their unpertu rbed velocity component perpendicular to B is larger than either their parallel component or the wave-induced velocity. We find that the reg ions of velocity space where both this process and emission take place widen upon increasing \B\, whereas the rates at which the latter occu r are, in general, decreasing functions of \B\.