Toroidal kinetic ηi-mode study in reversed-field pinch plasmas

The ion temperature gradient (ITG) driven electrostatic modes in reversed-field pinch (RFP) plasma are studied with the gyrokinetic integral equation. A systematic threshold study is carried out and the results are compared with that in tokamaks with similar geometry and reveal that the ITG modes in RFP configurations are more stable than in tokamaks. The physics mechanism for such difference is that shorter connection length in RFPs leads to stronger landau damping, which is dominant and ultimately determinant for the stability threshold. The results confirm and extend the previous conclusion obtained with the differential equation [S. C. Guo, Phys. Plasmas 13, 122510 (2008)]. In addition, the effects of magnetic gradient and curvature drifts, which induce important interaction driving the modes, are carefully investigated. The effects of safety factor, ratio of electron temperature to ion temperature, magnetic shear as well as finite Larmor radius are also studied.