Parameter study of parametric instabilities during lower hybrid wave injection into tokamaks

摘要

A parameter study of the parametric instability (PI) during lower hybrid wave injection into tokamak plasmas is performed based on its local dispersion relation. The drift kinetic model and the fluid model are employed, where both the E × B and E_() coupling terms are retained. The E_() coupling term is significant at a lower plasma density n_e or a smaller oblique angle δ_1 and then influences the density dependence of the PI. At a lower n_e the PI decaying into the ion sound quasimode (ISQM) dominates, while at a higher n_e the dominant PI is that decaying into the ion cyclotron quasimode (ICQM). A higher electron temperature T_e can diminish the PI growth rate for both ISQM and ICQM types, since an increasing T_e weakens the PI driving term, just like turning down the injecting power. A large background magnetic field B_0 may reduce the PI growth rate, but this effect is rather weak on the ISQM-type PI at a lower n_e .