Coupling of slow and fast ICRF waves to H-mode plasmas

Radial currents are used to modify the plasma edge in CCT through the j × B force, which results in poloidal rotation for 0.9 < r/a < 1.0. An H-mode like state is achieved, where a transport barrier is established near the plasma edge in ohmic discharges. When the barrier is present, the plasma density at the antenna surface is reduced, resulting in a large decrease in the coupling of the IBW antenna. The coupling of the ICRF antenna may improve, provided that the resulting steeper edge density gradient offsets the effect of the "vacuum gap" in front of the antenna. Nevertheless, the design requirements of ICRF antennas for H-mode plasmas may prove to be difficult, whereas that of the IBW antenna unrealistic.