Theory of Pulse Stimulated Radiation from a Plasma Caused by the Relativistic Mass Effect

A plasma excited by two short pulses at the electron gyrofrequency which have a time separation τ, is considered in the single particle approach. It is shown that the relativistic mass effect can lead to a series of radiation maxima after the second pulse. In the case of a cold plasma in an inhomogeneous magnetic field these maxima arise at multiples of the time τ; in the case of a hot plasma in a. homogeneous magnetic field at multiples of τ/|1 ± D|, where D is the strength of the second pulse relative to the first one. The shape of the radiation maxima is given by the square of the Fourier transform of the distribution of the inhomogeneities or the initial energies, respectively. The two effects have the tendency to cancel each other. If the plasma is excited by three pulses, the time separation of the second and third pulse being T , radiation maxima occur at times t = Kτ + LT, (±K, L = 0, 1, 2 . . . but t > 0) after the third pulse in the case of a cold plasma with field inhomogeneities, and at t = (Kτ + LT)/|1 ± D ± D_2| in the case of a hot plasma. If collisions are taken into account the dependence on T of the radiation maxima with L = 0 is determined by inelastic collisions only, while the other decay times are determined by all kinds of collisions.