Parametric decay into ion cyclotron waves and drift waves in multi-ion species plasma

Parametric decay processes near the ion cyclotron frequency are investigated experimentally and theoretically in multi-ion species plasmas. The relevant theoretical dispersion relation of the parametric coupling is derived, including the ion drift motion. Experimental data obtained in the Princeton L-4 device verify these theoretical predictions in some detail. In a helium-neon plasma, the relative ion drift motion excites electrostatic ion cyclotron waves (the kinetic ion-ion hybrid mode) when ω0≳ΩHe +ΩNe. In a region of large density gradient, the ion drift motion also excites low-frequency drift waves when ω0≳ΩHe+ω*. The experimental data are found to agree well with the theory. The relevance of these processes to ion cyclotron heating of fusion plasmas is discussed.