Symmetric neutralized ion beams for magnetic fusion applications

A symmetric neutralized ion beam (SNIB) is composed of positive and negative ions, and is capable of propagating across a transverse magnetic field due to the polarization of the beam. Such a beam may be of use as an alternative or complement to conventional neutral beam injection (NBI) in magnetic confinement fusion devices. SNIBs of energies from hundreds of keV up to a few MeV can be efficiently produced through a novel application of radio frequency quadrupole (RFQ) accelerators. Because the cross-field propagation ability of the SNIB depends mainly on beam density, SNIBs of significantly lower energy than the 1 MeV envisioned for ITER neutral beams can in principle reach the center of a magnetically confined plasma. Some challenges that need to be overcome for this technique to be viable are identified; nevertheless, the approach is attractive when compared to the bulky, high voltage, conventional neutral beam systems. Distributed injection of many beams is possible due to the relative compactness of a SNIB module.