Magnetic Helicity Injection Mechanism for Double-Null Startup of the UTST Spherical Tokamak Plasmas

Abstract

A close relationship between magnetic helicity injection and magnetic reconnection was observed during double-null formation of spherical tokamak (ST) plasmas. The magnetic reconnection of common flux into private flux causes concentration of current density along the current sheet, forming a high eigen-value area between the helicity source (coil flux) and the ST plasma. The formation of a plasmoid and its translation to core plasma indicate intermittent translation of the high eigen-value area, suggesting a mechanism for helicity injection.