Bremsstrahlung at Low-Energy Electron–Nucleus Collisions in a Quantizing Magnetic Field. II. Close Collisions with Quasibound Motion

We analyze electron–nucleus collisions in a strongly magnetized ideal plasma with a low temperature at which the Coulomb interaction energy of particles at a distance of the order of the electron Larmor radius exceeds their thermal energy. In this limit, the motion of the electron in close collisions becomes quasibound. Analytical expressions for the spectral power of bremsstrahlung in the continuum at frequencies where quasibound motion makes a decisive contribution to the emission have been obtained. The proposed quantum approach is valid both in the limit of such a low energy of an electron that the latter can occupy only a fundamental Landau level before and after the collision and in the limit of classical particle motion. In the classical regime, the radiation losses approximately preserve the trajectory of the particle: the emission of a photon just changes the phase incursion of the electron wave function by the same amount within the cross section of a beam of rays approximating the state of the particle. A condition is formulated under which spontaneous emission puts the particle into a superposition of states essentially differing from the initial state by the probability for the electron to occupy different Landau levels after the collision. This emission regime takes place in the low-temperature plasma of the photosphere of a white dwarf in the infrared continuum.