Observation of ablation and acceleration of impurity pellets in the presence of energetic ions in the CHS heliotron/torsatron

Hydrocarbon pellets were injected into NBI and ECH plasmas of the Compact Helical System (CHS) heliotron/torsatron. The ablation of the pellet was observed from horizontal and vertical directions using two CCD cameras, and the velocities of the pellet during ablation were measured with an 11 channel fan array. It was observed that the pellet trajectory was strongly curved in NBI cases, whereas in ECH cases it was straight. When the toroidal direction of the tangential NBI was changed from clockwise to counter-clockwise, the direction of the curved trajectory completely changed. For the first time, it was also found that the pellet was accelerated during the ablation, for example from 270 to 600 m/s. The ablation of the pellet is simulated for the case with fast ions from NBI (40 keV). The results strongly support the idea that the pellet can be mainly ablated by collisions with fast ions. As a result, it is found that the pellet is accelerated by a jet of the ablation cloud resulting from one-side heating due to the toroidally circulating fast ions.