High- β Plasmoid Drift during Pellet Injection into Tokamaks

The outward acceleration of enhanced- β plasmoids formed when a frozen hydrogen pellet is injected into a hot tokamak plasma has been directly observed. The plasmoid characteristics, acceleration, and velocities measured agree with theoretical expectations. The plasmoid motion is always in the positive major radius direction, consistent with high fueling efficiency for high-field side, and rapid mass loss for low-field side injection. In parallel a weak acceleration of the ablating pellet itself in the same direction was observed, probably caused by a net radial rocket force component.