Measurement of large displacements of the toroidal current centroid using an external coil diagnostic

Several sinusoidal and saddle coils have been used to measure the toroidal current centroid of discharges produced in a pulsed tokamak experiment. Careful analysis of the external coil measurements and elaborate calibrations made the measurements possible even for large displacements of the plasma current and the noncircular geometry of the diagnostic coils. The calibration techniques and the data analysis formula are described, and examples of the use of the external coils to measure m=1 kinks of unstable toroidal Z‐pinch discharges are presented.