Determination of Eddy-Current Distribution in Electrically Isolated Vessel Sections of ADITYA-U Tokamak

Abstract

The time-varying magnetic field induces eddy current in the conducting structure of a tokamak device. The characteristics of eddy currents in the discontinuous vacuum vessel are more complex than those found in a tokamak with a continuous vacuum vessel. Even with multiple electrically isolated sections of the vacuum vessel, there is evidence of a noticeable fast decaying current that flows along the inboard and outboard vessel surfaces and their analysis is not straightforward. It is necessary to detect and investigate the eddy-current effect due to the close vicinity of the vessel surface with the plasma column as they seriously affect the in-vessel magnetic diagnostics, the penetration of equilibrium fields, and the displacement of the plasma column. The induced eddy currents in vacuum-vessel sections are estimated using magnetic probes during the in situ calibration experiments in ADITYA-U tokamak. The filament model is utilized for estimating the spatial and temporal eddy-current profiles generated in the ADITYA-U vacuum vessel. The number of current filaments in the vessel section is optimized using the various combinations of available Mirnov sensors (magnetic probes) located over the poloidal periphery inside the vessel. In this article, the eddy-current measurement under different experimental conditions in the ADITYA-U is presented. This study also serves as an illustration of the usefulness of the filament model for the parameterization of eddy-current paths and magnitude to describe the induced vessel current during ADITYA-U plasma discharges.