Trapped electron effects onηi-mode and trapped electron mode in RFP plasmas

The drift instabilities in the toroidal reversed field pinch (RFP) plasmas are numerically studied with gyrokinetic integral eigenmode equations, by taking into account the trapped electrons (TEs) and full ion kinetic effects. Both the collisionless and collisional plasmas are investigated. Two topics are addressed: the TE effects on the ion temperature gradient driven mode, and the instability of the trapped electron mode (TEM). A comparison with a circular tokamak configuration has been made. Although the TEs generally play a similar role in RFPs as they do in tokamaks, their effects become significant in RFPs only when very steep density/temperature profiles exist. Indeed, the instability of the TEM in RFP plasmas requires a much steeper density/temperature gradient and has a much narrower k θ ρ s spectrum than in tokamak plasmas.