Investigations of H-mode plasmas triggered directly by pellet injection inthe DIII-D tokamak

The transition from low-confinement (L-mode) to high-confinement (H-mode) p lasmas has been directly produced by injecting frozen deuterium pellets in the DIII-D tokamak. K-mode transitions were produced at edge electron and i on temperatures below the L-mode values. This implies that a critical edge temperature is not necessary for H-mode transitions. The experimentally det ermined edge plasma parameters were well below those predicted by several t heories of the H-mode transition to trigger the H-mode, indicating a need f or revision of these theories.