Initial ICRF coupling and heating experiments on Alcator C-Mod

Initial ICRF coupling studies were performed successfully on the Alcator C-Mod tokamak with all-metallic first wall, using a radially movable single-current-strap (monopole) antenna. The plasma loading is 10–40 times the vacuum loading, which is sufficient to inject 2 MW of r.f. power through one two-strap (dipole) antenna. The observed loading is consistent with predictions of full-wave calculations. Up to 1 MW of r.f. power (antenna power density of ≳ 10 MW m−2) has been injected into the C-Mod plasma without serious impurity problems. Definite signs of both ion and electron heating were observed at power levels of 0.4 MW and higher (PRFPOH ≳ 0.3) in the D(H) minority heating regime. High-power heating experiments with 4 MW of source power and two dipole antennas began in May 1994.