Interior Magnetic Field Fluctuation and Profile Measurements on Mst

Abstract

Understanding plasma stability and confinement in a reversed-field pinch (RFP), or any toroidal confinement device, requires detailed information on the poloidal magnetic field and current density distribution. The stability of the plasma to tearing modes and other MHD events such as the sawtooth perturbation or dynamo are closely related to the current density profile. In RFP’s, resistive MHD instabilities can produce magnetic islands on rational surfaces that are closely spaced in radius causing magnetic stochasticity resulting from island overlap. Energy transport in conventional RFP plasmas is believed to arise mainly from particles streaming along these stochastic magnetic field lines. For the Madison Symmetric Torus (MST), a major goal is to reduce magnetic fluctuations through current density profile control. Elucidating the physics of this interplay requires high-resolution measurement of both the current density profile time evolution and magnetic fluctuations.