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

Tokai Helicon Device (THD), which has been used to study lower-hybrid cavitons [1], is a helicon-type plasma device which utilizes a specially designed flat segmented multi-loop antenna to excite a helicon wave. The antenna, which is installed just outside a quartz window at the end of the vacuum vessel (20 cm i.d. and 100 cm length), consists of four concentric loops [2]. Each loop is divided into several segments. By changing the electrical connections among the antenna segments, it is possible to excite $m$ = +-1 and +-2 modes as well as $m$ = 0 mode, where $m$ is the azimuthal mode number. The discharge characteristics of the $m$ = 0 excitation cases were previously reported in detail [2]. The discharge characteristics of the $m$ = +-1 and +-2 cases will be presented. Excited wave characteristics of produced plasma will also be discussed. We have been using THD to develop a new plasma acceleration scheme for an advanced concept electric propulsion system. This application will be briefly discussed.\\[4pt] [1] T. Tanikawa \textit{et al}., Bull. Ameri. Phys. Soc. \textbf{54} (15), 125 (2009).\\[0pt] [2] T. Tanikawa \textit{et al}., Bull. Ameri. Phys. Soc. \textbf{51} (7), 164 (2006); T. Tanikawa and S. Shinohara, \textit{ibid}. \textbf{53} (14), 174 (2008).