Overview of Alcator C-Mod ICRF Experiments

In C-Mod, internal transport barriers (ITB) have been formed in both ohmic and offaxis ICRF discharges. With 0.6 MW of central ICRF, the density and impurity peaking is controlled and allows the ITB to be maintained for the duration of the ICRF. Mode conversion in both D(H) and H(u3He,D) has been investigated and the first measurement of D(H) mode conversion has been recently reported. A four-strap ICRF antenna has been shown to operate at high power density in heating phasing. Modifications have reduced the RF electric fields parallel to the magnetic field and shielded the BN-metal interfaces from the plasma. Voltage and power limitations were observed in the two dipole antennas and arc damage was found again where E ? B. Modifications have been completed and the initial antenna performance is presented.