Detection of slowly rotating n = 1 mode with signal compensation for an externally perturbed field in the KSTAR tokamak

Abstract

A mode identification method for slowly rotating (or non-rotating) n (toroidal mode number) = 1 plasma instabilities has been newly established with the signal compensation method used for an external time-varying magnetic field. The mode identification method is based on the Fourier decomposition scheme and processes the signal of the magnetic probes (MPs) on the passive stabilizer in the Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak. To exclude the non-plasma magnetic perturbation by the external current coils and their secondary eddy currents on the passive stabilizer that may not be easily characterized, the ARX-SISO (autoregressive with exogenous terms-single input single output) method has been introduced in the signal compensation process. Preliminary off-line analysis presented herein confirms that this method can adequately detect the time evolution of the mode-locking, along with a slowly rotating state, even in the presence of external magnetic perturbations.