MEASUREMENT OF THE OPTICAL DEPTH AT THE 3RD ELECTRON-CYCLOTRON HARMONIC IN TORE SUPRA

The linear relativistic theory of electron cyclotron wave propagation predicts partial absorption of the extraordinary mode at the third ele ctron cyclotron harmonic for typical parameters of present day tokamak plasmas. Since the waves are not totally damped, a quantitative confi rmation of such predictions is important to establish this particular resonance scheme firmly for plasma heating and current drive. Specific experiments have been performed on Tore Supra, to measure the optical thickness of the third harmonic extraordinary mode for vertical propa gation, over the full frequency spectrum. Comparison with ray tracing/ absorption calculations provides a direct validation of the linear rel ativistic theory.