The cooperative physical processes of ion source and ion beam physics in magnetic fields can be separated into plasma internal motions, motion from the source plasma into the beam, and beam formation. A few experiments demonstrate that these processes are consistent with elementary laws of charge diffusion. Ion beam current limits are almost independent of magnetic field and have magnitudes consistent with classical diffusion processes. Ion current is proportional to applied potential gradient up to high voltage breakdown values which are determined by electrode geometry and secondary electron currents. Beam plasma stability, which is necessary for isotope separation using ion beam technology, depends on the formation of a dense, charge-neutralizing plasma as well as on ion source stability. (auth)