Comparison of Experimentally Inferred and Simulated Impurity Transport Across Alcator C-Mod Confinement Regimes

Understanding and controlling the mechanisms of impurity transport are paramount for both prediction and optimization of burning plasmas. Despite documented challenges in inferring experimental impurity transport coefficients, recent efforts in computational statistics have suggested new pathways [Chilenski 15]. We present the results of inferences employing Bayesian model averaging, nested sampling and Gaussian processes. High performance computing tools have enabled the study of a range of confinement modes (including L-mode, EDA H-mode and I-mode) in Alcator C-Mod discharges. Trace CaF₂ impurities are introduced using Laser Blow-Off (LBO), with Ca dynamics diagnosed via spatially resolved X-ray measurements. Experimental transport coefficients are computed via iterations of the STRAHL code [Dux 06]. We present a comparison of experimental transport coefficients with turbulent TGLF [Staebler 07] and neoclassical NEO [Belli 08] simulations, focusing on the sensitivity of the results to subdominant unstable modes, Z_eff and velocity shear. Our results offer greater understanding of impurity dynamics in a wide range of confinement regimes and a promising path to gyrokinetic validation via particle transport.