CONFINEMENT AND PEDESTAL CHARACTERISTICS IN H-MODE WITH ECH HEATING

Access to the H-mode regime of improved confinement and good global confinement when the plasma heating is dominantly of the electrons is critical to the success of ITER, since the proposed heating schemes for ITER, including heating by fusion products, deposit most of their heat in the electron fluid. Most of the world database for the L-H transition and for confinement is derived from discharges with high power positive-ion neutral beam injection (NBI), which primarily heats the ions. Issues for dominant electron heating include the H-mode power threshold and effect on rotation, density profile, global confinement, pedestal height, and edge localized mode characteristics. Experiments have been performed on DIII-D using electron cyclotron heating (ECH) to simulate heating in ITER. These experiments suggest that the H-mode transition power for ECH is significantly lower than that for NBI in deuterium plasmas but about the same for helium plasmas. The global confinement with ECH relative to the H98(y,2) scaling is around 75% under the conditions of these discharges. The pedestal with pure ECH has a higher electron temperature and lower density than for NBI, and the width of the pedestal region is nearly identical.