Overview of recent alcator C-Mod results

Abstract

Research on the Alcator C-Mod tokamak is focused on exploiting compact high density plasmas to understand core transport and heating, the physics of the H mode transport barrier, and the dynamics of the scrape-off layer and divertor. Rapid toroidal acceleration of the plasma core is observed during ohmic heated H modes and indicates a momentum pinch or similar transport mechanism. Core thermal transport observations support a critical gradient interpretation, but with gradients that disagree with present theoretical values. High resolution measurements of the H mode barrier have been obtained, including impurity and neutral densities, and the instability apparently responsible for the favourable 'enhanced D alpha' regime has been identified. Divertor bypass dynamic control experiments have directly addressed the important questions surrounding main chamber recycling and the effect of divertor closure on impurities and confinement. Future plans include quasi-steady-state advanced tokamak plasmas using lower hybrid current drive.