Optimization of Energetic Particle Confinement in the W7-X Stellarator

Computational modeling is used to calculate the expected bootstrap current in the Wendelstein 7-X stellarator (W7-X) and determine the impact of this current on the confinement of energetic particles. The confinement of 60 keV ions in W7-X has previously been examined for the base W7-X configuration [M. Drevlak, J. Geiger, P. Helander and Y. Turkin, Nucl. Fusion 54, 073002 (2014)]. In this work, comparison of the base and a mirror W7-X configuration are analyzed, including the effects of increasing β and self-consistent bootstrap current. The confinement of energetic ions is analyzed as well with varying current in the planar coils. A long term goal of this work is to search for configurations with improved energetic particle confinement using stellarator optimization tools.