Analyzing Current Profiles in Magnetic Islands During RF Current Condensation

Magnetic islands in tokamaks can cause serious disruptions and contribute heavily to loss of confinement. These islands can be stabilized, and their disruption to confinement limited, by precisely steering RF-driven current into their centers. Typically, electron cyclotron or lower hybrid waves are used to drive current directly into the island centers; however, due to the movement of existing islands and formation of new ones, constant readjustment of the RF current drive is needed to ensure that current is localized to the island centers. Theoretical work has shown that current driven by electron cyclotron and lower hybrid waves naturally condenses at the centers of magnetic islands due to the heightened electron temperature there, eliminating the need for precise steering of the RF waves [1, 2]. To further our understanding of this effect, we will analyze and describe current profiles in the interiors of magnetic islands during RF current condensation.

[1] A. H. Reiman, Phys. Fluids 26, 1338 (1983).

[2] A. H. Reiman and N. J. Fisch, arXiv:1806.09260 [physics.plasm-ph] (2018).