Compressional Alfven and ion-ion hybrid modes in the deuterium-tritium plasma of a spherical tokamak power plant

A discrete spectrum of compressional Alfven eigenmodes and ion-ion hybrid eigenmodes is found to exist above the tritium ion cyclotron frequency in the deuterium-tritium (D-T) plasma of a spherical tokamak power plant (STPP) [H. R. Wilson et al., 19th IAEA Fusion Energy Conference (IAEA, Lyon, France, 2002), No. FT/1-4]. An equilibrium magnetic well formed in a STPP, as a result of plasma diamagnetism, causes all externally launched electromagnetic waves to propagate from the side of high total magnetic field, and it is this well that forms discrete spectra in the ion cyclotron resonance heating frequency range near the plasma core. The eigenmodes, as well as the position of the mode conversion layers, are obtained in a one-dimensional magnetic field geometry [S. C. Cowley et al., Phys. Fluids B 3, 2066 (1991)], relevant for the STPP, which will necessarily operate at high β. The possibility of using the discrete spectrum probed with an external antenna, or driven by energetic ions, for measuring the D-T mixture ratio is discussed