Equilibrium reconstruction of the q-profile in tokamaks from motional Stark effect data

The motional Stark effect (MSE) diagnostic has been implemented on the Tokamak Fusion Test Reactor (TFIR) and the Princeton Beta Experiment (PBX-M) to obtain q-profile measurements in the presence of a finite-β plasma. A multichannel MSE parameter system has obtained data for several plasma conditions including L-mode, Supershot, current ramps and high βp. Accurate measurement of the q-profile is essential for analysis of the equilibrium, stability and transport properties of a tokamak. Many externally observed phenomena, such as sawteeth and the beta collapse, can be analyzed principally in terms of the q and q (i.e., shear) profiles. Thus, the MSE measurement supplements the standard diagnostic suite of external magnetic probes to provide a new set of internal profile data which was previously unavailable. Using the MSE data, together with magnetic probe data, it is possible to obtain a self-consistent equilibrium reconstruction of the q-profile. Before describing the reconstruction technique, a brief review of the MSE diagnostic will be in this paper