Intrinsic rotation has been observed in $I$-mode plasmas from the $C$-Mod tokamak, and is found to be similar to that in $H$ mode, both in its edge origin and in the scaling with global pressure. Since both plasmas have similar edge $\nabla T$, but completely different edge $\nabla n$, it may be concluded that the drive of the intrinsic rotation is the edge $\nabla T$ rather than $\nabla P$. Evidence suggests that the connection between gradients and rotation is the residual stress, and a scaling for the rotation from conversion of free energy to macroscopic flow is calculated.

• Received 2 November 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.215001