  The propagation of charged particles through a scattering medium in the
presence of a magnetic field can be described by a Fokker-Planck equation with
Lorentz force. This model is studied both, from a theoretical and a numerical
point of view. A particular trace estimate is derived for the relevant function
spaces to clarify the meaning of boundary values. Existence of a weak solution
is then proven by the Rothe method. In the second step of our investigations, a
fully practicable discretization scheme is proposed based on implicit
time-stepping through the energy levels and a spherical-harmonics
finite-element discretization with respect to the remaining variables. A full
error analysis of the resulting scheme is given, and numerical results are
presented to illustrate the theoretical results and the performance of the
proposed method.
