Development of featured high-density helicon sources and their application to electrodeless plasma thruster

Helicon plasma sources using radio frequency (rf) waves are very useful, as they can produce high-density (~1013 cm−3) plasma easily with a broad range of external operating parameters. Various kinds of featured helicon sources in a wide range of geometrical scales have been developed and characterized to control plasmas as required. Furthermore, particle production efficiency has demonstrated excellent performance over a very wide range of plasma sizes. High-beta (~1) plasmas can also be easily achieved, showing the importance of the neutrals effect. As one of the many applications in areas ranging from fundamental to application fields, a space propulsion system with an advanced concept of an electrodeless condition (no direct contact between the plasma and electrodes/antennas) has been developed, owing to the expectation of a longer life operation. Among many proposals, two trials of electrodeless, additional acceleration methods are introduced, emphasizing the importance of some diagnostics. Here, we will review and describe the present status of our high-density rf plasma production with additional acceleration in an advanced propulsion field.