Alfven Wave Studies on Pretext.

Alfven wave heating experiments have been conducted on the PRETEXT tokamak. Theoretical developments of dispersion relations and polarizations of two Alfven modes lead to the Alfven resonance layer where a coupling mechanism (mode conversion) converts the compressional wave to the shear wave or to the kinetic Alfven wave. A coupling network is also required for matching the rf source and cable impedance to the antenna impedance. The design of a matching network and guidelines for impedance matching with plasma is discussed. An electronic processing unit has been designed and used for monitoring the change of antenna impedance or Q during the plasma discharge. Measurements on two antennas showed clearly that the antennas do interfere with each other and form a Fourier spectrum which alters the plasma loading resistance as predicted. The loading resistances are higher than those calculated from present theory. The dependence of the loading resistance on magnetic field has been observed, density dependence during plasma shots has not been clarified however. This is because that only "mush" loading can be detected through present arrangement, which is relatively insensitive to the density evolution during plasma shots.