Dimensionless Parameter Scaling of Intrinsic Torque in C-Mod Enhanced Confinement Plasmas

A dimensionless parameter dependence study of intrinsic torque has been performed on a database of H- and I-mode plasmas from the Alcator C-Mod tokamak. The torque was determined by comparing intrinsic angular momentum density profiles just before and just after L-H and L-I transitions. The intrinsic torque has been found to scale as $\beta _{\mathrm{N}}^{\mathrm{1.5}}\rho_{\mathrm{\ast }}^{\mathrm{-1.0}}\nu_{\mathrm{\ast }}^{\mathrm{0.1}}$ , with the parameter ranges 0.3 \textless $\beta_{\mathrm{N}}$ \textless 1.5, 0.004 \textless $\rho_{\mathrm{\ast \thinspace }}$\textless 0.011 and 0.04 \textless $\nu_{\mathrm{\ast \thinspace }}$\textless 0.9, and with the intrinsic torque varying between 0.04 and 0.6 Nm. Comparison with results from other tokamaks suggests that the intrinsic torque should be normalized by some measure of the device size. Normalizing to the major radius yields a scaling proportional to 1/$\rho_{\mathrm{\ast }}$ at fixed $\beta _{\mathrm{N}}$ (around 1.3), and an intrinsic torque value of 4 Nm for SPARC with R $=$ 1.85 m and $\rho_{\mathrm{\ast }} \quad =$ 0.0027.