Effects of cusped magnetic field on the discharge characteristics of helicon plasma

A new magnetic field configuration is proposed by introducing a cusped field to the helicon plasma thruster (HPT), and the effects of the cusped field on the discharge characteristics of the HPT are investigated. The experimental results show that the thruster can still achieve a stable W mode discharge with the additional cusped field, while the discharge conditions have been changed so that a higher RF power is required to achieve the W mode under the same experimental conditions. However, the ion density in the plume region is increased by at least one order of magnitude and the ion flux density is increased by a factor of 4 to 5. The ionization enhancement is attributed to the change in magnetic field configuration, which improves the energy coupling efficiency and the ability to confine charged particles (particularly electrons). This magnetic confinement could employ more electrons to ionize the working medium atoms, and the ionization rate is enhanced. The increase in ion density leads to a reduction in the energy available for ion acceleration, resulting in a slight decrease in ion energy.