Determination of plasma shift in a stellarator from magnetic measurements

The poloidal magnetic field created by plasma currents in an ordinary stellarator is calculated. An analytical calculation is performed for a plasma column of ‘average’ circular cross-section in the large-aspect-ratio approximation. The problem of determining the position of the column from poloidal magnetic field and flux measurements is investigated. A formula is obtained which links the plasma shift relative to the geometric axis of the stellarator with measurable quantities, and a simple system of magnetic measurements is proposed. The analysis is performed for a finite-beta plasma with allowance for longitudinal current and the external transverse field.