RECENT PROGRESS ON DISCHARGE CHARACTERISTICS OF HELICON PLASMA

Helicon plasma is one of the highest density plasma sources for generating the low-temperature plasma nowadays. It has great application potential in the fields of material processing, thin film deposition, aerospace propulsion, magnetic confinement fusion, and basic plasma physics research. It has received extensive attention from researchers worldwide in recent years. However, people lack in-depth understanding of the discharge theory of helicon plasma. There are various hypotheses about the absorption of energy during plasma excitation and propagation. It is more recognized that energy deposition is achieved by coupling the helicon wave and TG wave in the helicon plasma. At the same time, many unique phenomena, such as low-field peak, mode transition, current-free double layer (CFDL), have been demonstrated during the helicon plasma discharge process, which cannot be explained uniformly. It is sure that the investigation on the discharge characteristics will help to deepen the understanding of the discharge mechanism of helicon plasma. In this paper, the basic research progress on helicon plasma in the past 15 years was reviewed from the aspects of discharge mechanism and discharge characteristics. The results of low-field peak phenomenon, mode transition, and CFDL phenomenon during helicon plasma discharge were summarized. Focusing on the research on the discharge characteristics of helicon plasma, the future directions were prospected, which provides support for understanding the coupling mechanism of helicon plasma discharge and realizing engineering applications.