Measurement of magnetic fluctuations in Heliotron E

The coherent magnetic oscillations (frequency ≤ 20 kHz) are studied in currentless NBI heated plasmas by six magnetic probes. The toroidal/poloidal mode numbers (M/N) of oscillations are found to be (2/1, 1/1, 2/3). Bθ(M = 2/N = 1) is consistent with SX detected just after the internal disruption near the τ = 0.5 surface. Bθ(M = 1/N = 1) has a good correlation with ne, whose mode is consistent with the M = 1/N = 1 mode. Bθ(M = 2/N = 3) is observed in the case of a broad density profile by carbonization of the wall. Correlation analysis is useful to identify the mode numbers of these oscillations even if these are not clearly visible in raw signal. High frequency (20 ≤ f ≤ 100 kHz) unknown mode oscillations are detected even in low β plasmas, and are thought to be from the edge region. (author)