ICRF and Alfven wave heating experiments in Macrotor and Tokapole II tokamaks

A variety of ICRF wave launchers have been tested in Macrotor to determine the plasma edge response and wave excitation efficiencies. Three types of coupler were used: localized and distributed transverse loops and a longitudinal loop. Longitudinal loop exciters were also used in the Tokapole II tokamak to study the excitation of slow Alfven waves, where the shear Alfven resonance was demonstrated by direct probe measurement of the wave magnetic field within the plasma. The resonance is identified as radially localized enhancements of the poloidal wave magnetic field, and agrees with theory in its radial location, polarization, radial width, risetime and wave enhancement. In Macrotor, the cavity eigenmodes and the electrostatic ion cyclotron waves were excited at higher power. Edge plasma problems and the related impurity generation and density loss were avoided with the new distributed antenna, while heating and current drive were observed. Current initiation and ramp-up have also been observed in modest amounts (1 kA), improving with, but not requiring, a vertical field for initial momentum selection. Rather, the current direction is determined by the relative phase of the antenna sectors. (author)