Experimental observations of naturally occurring dust using a high-speed vacuum ultraviolet imaging system in EAST

In the ELMy H-mode experiment, naturally occurring dust originating at the high-field side is clearly observed using the high-speed vacuum ultraviolet imaging system developed on the Experimental Advanced Superconducting Tokamak (EAST). The main ablation cloud shape is similar to the classical shape observed in pellet fueling experiments. However, during the dust penetration, an erupted secondary cloudlet with a bent ‘cigar’ shape is observed and moves upwards along the direction perpendicular to the magnetic field line, which is different to the obviation in the pellet fueling experiments. This may be due to the ion diamagnetic drift effect. The velocities of the secondary cloudlet are estimated to be 50‒80 m s −1 . In addition, a significant degradation of the plasma confinement is observed during the dust penetration.