Study of Nonlinear Behavior of Low-Frequency MHD Mode Caused by Transition of Radial Electric Field in LHD

Abstract

The response of low-frequency magnetic fluctuations in a transition of radial electric field (E r ) is investigated in the edge region of LHD plasmas. Consequently, the amplitude of a magnetic fluctuation with f 2 -5 kHz is suddenly enhanced at the transition timing of E r , and then disappeared after the transition of E r . Furthermore, it is found that the amplitude of H α signals is enhanced, corresponding to the abrupt diminishing of the magnetic fluctuation with f 2 -5 kHz.

MyView2, a new visualization software tool for analysis of LHD data

“…Using the MyView2 software, the interesting plasma physics of the LHD is investigated rapidly. From this visualized data it is found that the magnetic fluctuation with f ∼ 2-5 kHz is suddenly enhanced at the timing of the change of the poloidal rotation velocity in the last closed flux surface of the plasma [16].…”

Spatial structure of low-frequency fluctuations throughout the transition of poloidal flow velocity in edge plasmas of LHD

“…In this paper, we investigated the spatiotemporal structure of a low-frequency fluctuation in edge plasmas, which emerges at the transition of V h (which is roughly identical with the E r ) of Large Helical Device (LHD). 15 For the stellarator geometry physics, there is no large toroidal rotation because of the parallel viscosity in the toroidal direction; 16 hence, E r is mainly determined by the poloidal flow velocity V h . Furthermore, the microwave Doppler reflectometer system is the most suitable for measuring the specific local density fluctuations.…”