Coupling Properties of Phased Waveguides in LHRF Heating Experiment in JFT-2 Tokamak

Abstract

A phased array of four waveguides was used as the wave launching system in an LHRF heating experiment in the JFT-2 tokamak. The coupling properties, particularly the reflection coefficient were investigated up to a power of 250 kW. The lack of dependence of the reflection on the phase difference Δφ at the high power of 70 kW obtained in an early experiment with an aluminium launcher is well explained by a theory in which the dissipation due to discharge is taken into account. After the launcher was improved in order to suppress the discharge, the reflection depended on Δφ even at a high power of 100 kW. Also, the reflection depended on the power density up to 16 MW/m2. This result agrees with these obtained from a linear theory in which a small modification due to ponderomotive force is incorporated.