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 ne or a smaller oblique angle δ1 and then influences the density dependence of the PI. At a lower ne the PI decaying into the ion sound quasimode (ISQM) dominates, while at a higher ne the dominant PI is that decaying into the ion cyclotron quasimode (ICQM). A higher electron temperature Te can diminish the PI growth rate for both ISQM and ICQM types, since an increasing Te weakens the PI driving term, just like turning down the injecting power. A large background magnetic field B0 may reduce the PI growth rate, but this effect is rather weak on the ISQM-type PI at a lower ne.
Ion cyclotron and spin-flip emissions from fusion products in tokamaks