Bursting high-frequency fluctuation observed in biased plasma in TU-Heliac

Abstract

In the biased plasma in TU-Heliac, a steep density profile around the core plasma region suddenly collapsed, accompanied with a high-frequency bursting turbulent fluctuation (100 kHz < f < 500 kHz). Envelope analysis was applied and the moment of the bursting event occurrence was detected in the biased plasma. The profile of the density gradient and bursting fluctuation were obtained using two Langmuir probes, one as a monitor probe for the bursting fluctuation and the other as a profile scan probe with a conditional average method. The fluctuation increased and showed a peak at the low field side of the steep gradient, from which the fluctuation propagated to the inner and outer directions at a velocity of 1 km s−1. The density gradient and the fluctuation had a non-linear relation and indicated a hysteresis loop.