The propagation of a dense quasi-neutral ion beam across a magnetized plasma

Propagation of a quasi-neutral narrow ion beam across a magnetised cold plasma is investigated in slab geometry. This problem is of interest in connection with artificial beam injection experiments and with naturally appearing plasma injections into magnetic fields as astrophysical jets. Several different cases are discussed briefly where the beam is assumed either slow or fast. For fast beams it is shown that they propagate due to generation of a polarisation electric field even in the case of presence of a background plasma. Slow beams can depolarise by currents flowing into the beam along the field lines and providing the required electrons for charge neutralisation. Some implications of the model are discussed in the context of recent active beam injection experiments into space plasma.