Observation of ICRF Mode Conversion Plasma Flow Drive on Alcator C-Mod*

Plasma flow driven by externally launched rf waves could be important in stabilizing micro- and macro-instabilities in tokamaks. We report the first observation of both toroidal (V$_{\phi })$ and poloidal (V$_{\theta })$ flows driven via an ICRF mode conversion (MC) process in D($^{3}$He) plasmas. At modest $^{3}$He levels (n$_{3He}$/n$_{e}\sim $ 8{\%}), in relatively low density plasmas, $<$n$_{e}>\le $ 1.3$\times $10$^{20}$m$^{-3}$, heated with 50 MHz rf power (B$_{t0}\sim $ 5.1 T), strong V$_{\phi }$ in the co-current direction is observed by high-resolution x-ray spectroscopy. The central V$_{\phi }$ scales with the applied rf power ($\le $ 30 km/s per MW), and is at least a factor of 2 more than the empirically determined intrinsic plasma rotation [1]. The rotation near the plasma center (r/a $<$ 0.3) responds more quickly to the applied rf power than the outer region, indicative of a local flow drive source. Localized poloidal rotation (0.3 $\le $ r/a $\le $ 0.5) in the ion diamagnetic drift direction is observed when P$_{rf }\ge $ 1.5 MW and increases with power ($\sim $ 2 km/s at 3 MW). Turbulence spectrum broadening seen by a phase contrast imaging (PCI) system indicates strong flow also exists in the main ions. The mode converted ion cyclotron wave (MC ICW) is observed by PCI and confirmed by 2-D full wave TORIC code simulation. The simulation result shows that due to the up-shifted k$_{\vert \vert }$,$_{ }$the MC ICW is strongly damped on $^{3}$He ions in the vicinity of the MC layer, approximately on the same flux surfaces where poloidal flow is observed. The involvement of ion heating and short-wavelength slow wave is consistent with theoretical considerations for efficient rf flow drive. Our experimental results are comparable to the predictions [2], assuming similar ion interaction mechanism for the MC ICW and direct launch ion Bernstein wave. The feasibility of ICRF flow drive on ITER will be discussed. [1] J. E. Rice, et al, Nucl. Fusion \textbf{47}, 1618 (2007). [2] J. R. Myra and D. A. D'Ippolito, Phys. Plasmas \textbf{9}, 3867 (2002).