Penetration of filamentary structures into the divertor region of spherical tokamaks

Abstract

Understanding the penetration from the midplane region towards the divertor plate of filamentary structures in the main scrape-off layer of spherical tokamaks is of interest for divertor design and plasma material interaction. Insight into this problem is gained by studying the closely related problem of the parallel structure of resistive ballooning modes, localized to a particular flux surface by a perturbed blob-like density profile. The resulting linearized equations are solved using the Arbitrary Topology Equation Reader code. A metric applied to the spatial structure of the dominant eigenmode quantifies mode penetration. Trends in this quantity are then measured by performing parameter scans over temperature and density. The results of this study are consistent with the dominant role of collisionality in limiting mode interaction with the divertor plate.