On the $\rho_{\mathrm{\ast }}$ Scaling of Intrinsic Rotation in C-Mod Plasmas with Edge Transport Barriers*

Changes in the core intrinsic toroidal rotation velocity following L- to H- and L- to I-mode transitions have been investigated in Alcator C-Mod tokamak plasmas. The magnitude of the co-current rotation increments is found to increase with the pedestal temperature gradient and q$_{\mathrm{95}}$, and to decrease with toroidal magnetic field. These results are captured quantitatively by a model of fluctuation entropy balance which gives the Mach number M$_{\mathrm{i}}$ \textasciitilde $\rho_{\mathrm{\ast }}$/2 L$_{\mathrm{s}}$/L$_{\mathrm{T}}$ \textasciitilde gradT q$_{\mathrm{95}}$/B$_{\mathrm{T}}$ in an ITG turbulence dominant regime. The agreement between experiment and theory gives confidence for extrapolation to future devices in similar operational regimes. Core thermal Mach numbers of \textasciitilde 0.07 and \textasciitilde 0.2 are expected for ITER and ARC, respectively.