Transport and focussing of intense electron and ion beams using external magnetic fields and plasma channels

The propagation of intense electron and ion beams (currents of a few megaamperes at the megavolt level) over long distances is analyzed theoretically and compared to recent experimental results. Two schemes are presented: the use of axial magnetic fields for ion beam propagation and focussing onto small targets and the use of current-carrying plasma channels for either electron- or ion-beam propagation. The problem of current neutralization is dealt with by using Maxwell´s equations and finite resistivity of the plasma channel. It is shown that the most important effect is the high inductance of any external path for the return current compared to the low inductance (including the possibility of negative inductance) of the channel where the beam propagates. Self-consistent fields are derived and beam-particle orbits are calculated. Limits on current propagation and focal size are presented. Recent experimental results of e-beam propagation in a current-carrying plasma channel will be briefly reviewed.