East Shows Different Spontaneous Rotation Behavior under LHCD

ASIPP scientists find on EAST for the first time that LHW can induce co-current rotation both in the core and edge plasma on EAST. A paper on the experiment and its theoretical analysis is published on Phys. Rev. Lett. 106, 235001,2011. The plasma rotation under LHCD is measured using the newly developed X-ray crystal spectrometers (Plasma Phys. Control. Fusion, 52, 085014, 2010) and fast reciprocating probe system (Rev. Sci. Instrum., 81, 113501, 2010).

　  Plasma rotation has demonstrated its important role which it plays in L-H mode transition, the formation of internal transport barrier (ITB), and the suppression of turbulence and MHD instabilities. In recent years, lots of research has been focused on the spontaneous rotation driven by RF waves, because it might generate the amount of rotation required for steady-state operation of ITER and future fusion reactors, for which NBI may not be efficient enough due to the large machine size and high density and limits in NBI itself. 

　  Different from the phenomena observed on other tokamaks, the EAST results demonstrate that in low-density L-mode plasma discharges, LHW could produce co-current rotation and the change in internal inductance has no obvious correlation with the rotation as observed previously by others. The results also show that the change in the rotation is much faster at the edge than in the core, <100ms vs. 1s, indicating the momentum might be possibly transported from the edge to the core. A model based on turbulence equipartition theory and thermoelectric pinch is able to predict the change in the core rotation with good agreement in the time scale with the experiments. It is believed that the new observations on EAST will complement the current research on the spontaneous rotation and also promote the understanding of the mechanism governing the plasma momentum transport. (Lu Bo reports)