Helicon plasma generation at very high radio frequency

Abstract

Helicon plasmas were produced using a very high radio frequency (RF) (98 MHz) source which is commonly used for radio communication. As in the plasmas generated at lower frequency such as 13.56 MHz, E-H-W mode transitions were observed. In the helicon mode, a bright column was produced at the central part of the cylindrical plasma. Experiments using Nagoya type III antennae with different leg lengths showed that the antenna having the shortest legs produced the highest density, which suggests the importance of the antenna ring section. A study of the operation window of the helicon plasma at 98 MHz demonstrated that the H-W mode transition occurs at lower magnetic field at higher gas pressure with the RF power fixed. It was also observed that the transition arises at lower magnetic field at higher RF power with the gas pressure fixed, indicating the correlation between the three important operating parameters on helicon plasma generation and sustainment.