Perturbed Ion Temperature and Toroidal Flow Profile Measurements In Rotating Neoclassical Tearing Mode Magnetic Islands

We present concurrent measurements of toroidally and radially resolved perturbed electron temperature (Te), ion temperature (Ti), and ion toroidal flow (vi) profiles within magnetic islands [1]. Both Te and Ti perturbations exhibit maxima near the island separatrices, with phase shifts of π at the island center, consistent with expectations. Notably, while Te remains nearly flat at the O-point, Ti exhibits a steep gradient. The perturbed vi has minima at the O-points and maxima at the X-points, indicating a deceleration of ions within the O-points. The flow phase is constant across the island but jumps by π outside of the separatrices.

Within experimental uncertainties, Reduced Drift Kinetic simulations, are in accord with the measurements [1]. Notably, the inclusion of fast ions restores the Ti gradient across the island O-point for medium island widths. This arises from the combined effect of parallel streaming and magnetic drifts associated with fast, passing ions. Consequently, this reduces the bootstrap drive for NTMs. Polarization currents are affected via the perturbed radial electric field. These measurements are crucial in constraining theoretical models predicting the NTM onset threshold scaling for ITER and other next-generation tokamaks