Modification of a limiter under ultra long pulse operation in the superconducting high-field tokamak TRIAM-1M

Morphological and compositional changes have been investigated for a ring limiter of the superconducting high-field tokamak TRIAM-1M after hydrogen plasma discharges, including very long duration (3 min) operation. The limiter surface was found to be complicatedly modified by synergistic effects of heat load, hydrogen bombardment and impurity accumulation. Particularly, heavy damage was observed in the inner part of the torus on the plasma side. This is considered to be caused by long heat loading under long pulse discharge. Present work implies new issues for the limiter and wall materials to be used for steady-state tokamak devices. (orig.)