Spontaneous toroidal rotation driven by the off-diagonal term of momentum and heat transport in the plasma with the ion internal transport barrier in LHD

Abstract

A spontaneous rotation in the co-direction is observed in plasmas with an ion internal transport barrier (ITB), where the ion temperature gradient is relatively large (∂Ti/∂r ∼ 5 keV m−1 and ) in LHD. Because of the large ion temperature gradients, the magnitude of the spontaneous toroidal flow, , becomes large enough to cancel the toroidal flows driven by tangential injected neutral beams and the net toroidal rotation velocity is almost zero at the outer half of the plasma minor radius even in the plasmas with counter-dominant NB injections. The effect of velocity pinch is excluded even if it exits because of zero rotation velocity. The spontaneous toroidal flow appears in the direction of co-rotation after the formation of the ITB, not during or before the ITB formation. The causality between the change in and ∂Ti/∂r observed in this experiment clearly shows that the spontaneous rotation is driven by the ion temperature gradient as the off-diagonal terms of momentum and heat transport.