Ulrich Kolberg


Spontaneously emitted field fluctuations in astrophysical plasmas(pdf)

Any fully-ionized collisionless plasma with finite random particle velocities contains electric and magnetic field fluctuations. The fluctuations can be of three different types: weakly damped, weakly propagating or aperiodic. The kinetics of these fluctuations in general unmagetized plasmas, governed by the competition of spontaneous emission, absorption and stimulated emission processes, is investigated, extending the well-known results for weakly damped fluctuations. The generalized Kirchhoff radiation law for both collective and non-collective fluctuations is derived, which in stationary plasmas provides the equilibrium energy densities of electromagnetic fluctuations by the ratio of the respective spontaneous emission coefficient and the true absorption coefficient. As an illustrative example the equilibrium energy densities of aperiodic transverse collective electric and magnetic fluctuations in an isotropic thermal electron-proton plasmas of density $n_e$ is calculated as $|\del