Observation of Ion-Cyclotron-Frequency Mode-Conversion Flow Drive in Tokamak Plasmas

Abstract

Strong toroidal flow ($V_{\varphi }$) and poloidal flow ($V_{\theta }$) have been observed in D-${}^3\mathrm{He}$ plasmas with ion cyclotron range of frequencies (ICRF) mode-conversion (MC) heating on the Alcator C-Mod tokamak. The toroidal flow scales with the rf power $P_{\mathrm{rf}}$ (up to $30\mathrm{km}/\mathrm{s}$ per MW), and is significantly larger than that in ICRF minority heated plasmas at the same rf power or stored energy. The central $V_{\varphi }$ responds to $P_{\mathrm{rf}}$ faster than the outer regions, and the $V_{\varphi }(r)$ profile is broadly peaked for $r/a\le 0.5$. Localized ($0.3\le r/a\le 0.5$) $V_{\theta }$ appears when $P_{\mathrm{rf}}\ge 1.5\mathrm{MW}$ and increases with power (up to $0.7\mathrm{km}/\mathrm{s}$ per MW). The experimental evidence together with numerical wave modeling suggests a local flow drive source due to the interaction between the MC ion cyclotron wave and ${}^3\mathrm{He}$ ions.