Effects of the local pressure gradient and the resistivity on interchange instabilities and high frequency fluctuations on Heliotron E plasmas

MHD instabilities accompanied with the sawtooth oscillations on the soft X-ray and FIR signals were observed when the limiter was inserted into the Heliotron E standard magnetic configuration plasma at high magnetic field (B = 1.9 T) and low beta value (β(0) < 1.0%). The poloidal m and toroidal n mode numbers m/n = 2/1, 3/2, 4/3, 5/4, 1/1 are identified by the Mirnov coil arrays. Some of the instabilities are thought to be destabilized by increasing the local pressure gradient near the rational surfaces in front of the limiter. In the smallest sized plasmas (lim ∼ 9 cm, ιlim ∼ 0.7), the highly coherent, high frequency magnetic fluctuations with mode numbers of m = 2 and n = 1 are found without the resonance surface (ι = 0.5) in the plasma. (author) 6 refs., 6 figs