Application of lower hybrid (LH) current drive in tokamak plasmas can induce both co- and countercurrent directed changes in toroidal rotation, depending on the core $q$ profile. For discharges with $q_0<1$, rotation increments in the countercurrent direction are observed. If the LH-driven current is sufficient to suppress sawteeth and increase $q_0$ above unity, the core toroidal rotation change is in the cocurrent direction. This change in sign of the rotation increment is consistent with a change in sign of the residual stress (the divergence of which constitutes an intrinsic torque that drives the flow) through its dependence on magnetic shear.

• Received 24 May 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.125003