Effect of electron temperature anisotropy on TEM in reversed-field-pinch plasmas

Abstract

Abstract For the first time in the reversed-field-pinch configuration, trapped electron mode (TEM) with anisotropies of electron temperature and its gradient is studied by solving the gyrokinetic integral eigenmode equation. Detailed numerical analyses indicate that TEM is enhanced by the anisotropy with temperature in the direction perpendicular to the magnetic field that is higher than that in the direction parallel to the magnetic field when the latter is kept constant. However, the enhancement is limited, such that TEM is weakened and even stabilized when the anisotropy is higher than a critical value, due to strong Landau damping. In comparison with the isotropic case, the lower Landau damping with the higher parallel electron temperature makes TEM instability easier to excite, which expands the TEM unstable region in the diagram of density and temperature scale lengths. In addition, it is found that the electron temperature gradient in the perpendicular direction offers a stronger driving force on TEM instability than that in the parallel direction. The overall effects of the temperature gradients of electrons and ions, magnetic shear, safety factor and density gradient on TEM in the presence of the anisotropies are presented in detail.