Particle Transport and Electron Density Relaxation due to Stochastic Magnetic Fields in the MST Reversed Field Pinch

Particle transport and its effect on the plasma density distribution remains an important, unresolved issue in magnetic fusion plasmas [1]. Fluctuating magnetic fields can arise from global tearing instabilities that often underlie the sawtooth oscillation [2] and lead to plasma relaxation [3]. Furthermore, magnetic fluctuations are also generated by energetic particles associated with non-inductive heating (NBI, ICRF) or inevitably generated intrinsically in burning plasmas by alpha particles. These fluctuations include various Alfvenic modes and energetic particle driven modes [4]. Conversely, stochastic magnetic fields have also been externally imposed (resonant magnetic perturbation) to mitigate the effect of edge localized modes (ELMs) by locally enhancing edge transport in Tokamaks [5]. Basic understanding of magnetic fluctuation-driven particle transport processes is thus of great interest and possibly critical to ELM control and fast particle losses in ITER. Progress to date is largely limited by the lack of direct measurements of the magnetic fluctuation-induced particle flux in hot plasmas.