Local dependence of ion temperature gradient on magnetic configuration, rotational shear and turbulent heat flux in MAST

Abstract

Experimental data from the Mega Amp Spherical Tokamak (MAST) is used to show that the inverse gradient scale length of the ion temperature R/L-Ti has its strongest local correlation with the rotational shear and the pitch angle of the magnetic field. Furthermore, R/L-Ti is found to be inversely correlated with the gyro-Bohm-normalized local turbulent heat flux estimated from the density fluctuation level measured using a 2D beam emission spectroscopy diagnostic. These results can be explained in terms of the conjecture that the turbulent system adjusts to keep R/L-Ti close to a certain critical value (marginal for the excitation of turbulence) determined by local equilibrium parameters (although not necessarily by linear stability).