Parametric dependence of fast-ion transport events on the National Spherical Torus Experiment

This paper presents an empirical approach towards characterizing the stability boundaries for some common energetic-ion-driven instabilities as seen on the National Spherical Torus Experiment (NSTX). Understanding the conditions for which beam-driven instabilities arise, and the extent of the resulting perturbation to the fast-ion population, is important for predicting and eventually demonstrating non-inductive current ramp-up and sustainment in NSTX-U (Menard J. et al 2012 Nucl. Fusion 52 083015), as well as the performance of future fusion plasma experiments such as ITER. A database has been constructed, based on shots from the 2010 experimental campaign for which TRANSP runs were performed. Each shot was divided into 50 ms intervals and the dominant beam-driven activity was characterized, and plasma parameters were collected into a database. It is found that TAE avalanches are present for βfast/βtotal > 0.3 and quiescent plasmas only for βfast/βtotal < 0.3. (paper)