Transport and bunching of light ion beams for pellet fusion

In the previous paper, Dr. Cooperstein discussed the techniques required to focus TW-level light ion beams extracted from pinch-reflex diodes to high current density [1–3]. In this paper, we consider several-meter transport of the focussed ion beam to inertial-confinement-fusion targets through a Z-discharge transport channel. This technique allows ion beams to be transported the distances required for reaction-chamber standoff and provides a means of combining beams extracted from many generators onto a single target. Referring to Fig. 1, the ion beam enters the Z-discharge channel at the best beam focus location. Inside the channel, the ions are confined radially by the azimuthal magnetic field produced by the discharge of an external capacitor bank. The 25–150 kA current in the channel is adjusted to provide radial confinement for ions with the maximum transverse energy. The plasma density in the channel must be sufficiently high to resist expansion forces during beam transit and sufficiently low to prevent excessive energy loss of the beam. A happy combination of desired transport length (2–5 m), proton or deuteron energy (2–5 MeV), and ion beam pulse duration (50–100 ns) permits axial bunching of the beam during transport by ramping the accelerator voltage in time. Beam power multiplication of the beam can be achieved in this fashion.