Propagation of intense charge-neutral ion beams in magnetic fields

The motion of intense space-charge-neutral ion beams along and across magnetic fields has been determined both experimentally and theoretically. We find that a beam will pass through a transverse field undeflected if the beam dielectric constant exceeds a threshold value or is otherwise reflected. We find that a beam propagating along a magnetic field is collectively focussed if the skin depth c/wpe exceeds the beam radius or is otherwise radially compressed at the Alfvén velocity.