The effect of magnetic configuration on ion acceleration from a compact helicon source with permanent magnets

Plasma production and emergent ion beam formation were examined in a compact helicon plasma source with different configurations of permanent magnets. Source modification employing a cylindrical ferrite assembly (CFA) with radial magnetization was found to produce high-density plasmas over a broad pressure range, but the ion beam was generated only at sub-millitorr pressures and provided that a pressure difference was set up between the discharge and the drift chambers. The modification employing the near field of a single annular ferrite (AF) was ineffective in both dense plasma and ion beam generation. The modification employing a combination of the AF with the CFA was found to be the most efficient for ion acceleration. It generated a fast ion beam with an energy of up to 200 eV in the sub-millitorr pressure range, and could produce the accelerated ions even in the millitorr range.