Characteristics of Helicon-Plasma Produced Using a Segmented Multi-Loop Antenna II

It has been demonstrated that a large-diameter (up to 74 cm), large-volume (up to 2.1 m$^{3})$ helicon plasma can be produced very efficiently (production of $\sim $10$^{15}$ ion-electron pairs per one-watt of rf power) by using a flat spiral antenna, which is installed just outside an insulator window at the end of a cylindrical vacuum vessel and is immersed in a non-uniform magnetic field [1,2]. The same principle has been applied to a smaller device (20 cm in diameter and 1 m in axial length), but using a somewhat different type of flat antenna, namely a segmented multi-loop antenna [3]. By changing the electrical connections among the antenna segments, it is possible to excite the azimuthal modes of higher than $m$ = 0 as well as the $m$ = 0 mode itself, where $m$ is the azimuthal mode number. Under certain conditions, it is possible to produce a non-uniform plasma along the uniform magnetic field due probably to the neutral depletion in the main plasma production region. The discharge characteristics of the device will be presented. [1] S. Shinohara and T. Tanikawa, Rev. Sci. Instrum. \textbf{75}, 1941 (2004); Phys. Plasmas \textbf{12}, 044502 (2005). [2] T. Tanikawa and S. Shinohara, Thin Solid Films \textbf{506-507}, 559 (2006). [3] T. Tanikawa \textit{et al.}, Bull. Ameri. Phys. Soc. \textbf{51} (7), 164 (2006).