Wave field structure and power coupling features of blue-core helicon plasma driven by various antenna geometries and frequencies

This paper deals with wave propagation and power coupling in blue-core helicon plasma driven by various antennas and frequencies. It is found that compared to non-blue-core mode, for blue-core mode, the wave can propagate in the core region, and it decays sharply outside the core. The power absorption is lower and steeper in radius for blue-core mode. Regarding the effects of antenna geometry for blue-core mode, it shows that half helix antenna yields the strongest wave field and power absorption, while loop antenna yields the lowest. Moreover, near axis, for antennas with m = +1, the wave field increases with axial distance. In the core region, the wave number approaches to a saturation value at much lower frequency for non-blue-core mode compared to blue-core mode. The total loading resistance is much lower for blue-core mode. These findings are valuable to understanding the physics of blue-core helicon discharge and optimizing the experimental performance of blue-core helicon plasma sources for applications such as space propulsion and material treatment.