Self-Organized Rotating Filament Structure in Plasma in the Large Helical Device After Tracer Encapsulated Solid Pellet Injection

A small tungsten grain encapsulated in a polystyrene pellet was injected into plasmas in the large helical device. The ionized tungsten was transported and accumulated in the plasma center to drastically drop the central electron temperature. A tangentially viewing fast framing camera observed a bubble-like structure expanding from the plasma center after the pellet injection. After that, a self-organized filament appeared on the surface of the bubble, and the filament began to rotate around the plasma center, which was stably sustained for ~0.22 s.