Co- and Counter-current Rotation Induced by Lower Hybrid Current Drive in Tokamak Plasmas

Lower Hybrid Current Drive (LHCD) induced rotation has been observed in Alcator C-Mod plasmas as well as in other devices. Recent experiments at Alcator C-Mod have for the first time identified the plasma conditions that determine the LHCD driven rotation direction, co- or counter-current, of the main ion species. This effect is found to depend strongly on the plasma current: low current plasmas have co-current rotation and higher current plasmas exhibit counter-current rotation. Experiments were performed to explore this dependence and changes in rotation were observed to approach 40 km/s at $<\!n_{e}\!>$=0.66e20 m$^{-3}$; the LHCD rotation reversal point, $\Delta$v=0, was also identified. There appears to be a magnetic field configuration effect with the favorable (unfavorable) $\nabla$B configuration having a rotation reversal point around $\sim$400 kA ($\sim$550 kA). In both co- and counter- current cases, rotation profiles show that the momentum originates near the core of the plasma. Analyses of plasma behavior and gyrokinetic simulations were performed and results are shown.