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 born at the high field side (HFS) is clearly observed using the high-speed vacuum ultraviolet imaging (VUVI) 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 bending ‘cigar’ shape is observed and moves upward along the direction perpendicular to the magnetic field line, which is different with 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 as 50-80 m/s. In addition, a significant degradation on the plasma confinement is observed during the dust penetration.