Z-discharge transport of intense ion beams for inertial confinement fusion

Ion inertial confinement fusion requires beam transport over distances of a few meters for isolation of the diode hardware from the target explosion and for power compression by time-of-flight bunching. This paper evaluates light ion beam transport in a wall-stabilized z-discharge channel, where the discharge azimuthal magnetic field radially confines the ion beam. The ion beam is focused onto the entrance aperture of the transport channel by shaping the diode to achieve beam convergence in a field-free drift region separating the diode from the transport section. Ion orbits are studied to determine the injection efficiency (i.e., the fraction of the beam emitted from the diode which is transported) under various conditions. Ions that are focused onto the channel entrance at too large of an angle for confinement hit the wall and are lost. For a multimodular scheme (10–30 beams), individual transport channels are packed around the target with the exit apertures at some standoff distance from it. The fraction of the beam that is lost in this field-free standoff region is also evaluated under various conditions. The standoff efficiency is then combined with the injection efficiency to give the dependence of the total transport efficiency ηt on diode, focusing, transport and standoff parameters. It is found that ηt can be in the range of 75%–100% for parameter values that appear to be achievable.