Turbulent Thermal Equilibration in Collisionless Magnetospheric Plasmas*

A planetary magnetosphere is a peculiar plasma environment where a high-temperature plasma is confined in a strongly inhomogeneous dipolar magnetic field generated by a planet. The high confinement is achieved by the inward pinch phenomena whereby particles are transported against the density gradient. It was demonstrated by gyrokinetic simulations that the turbulence driven by the magnetic curvature and density gradient (the entropy mode) leads to the particle pinch. In this work, we report that the entropy mode turbulence also has an effect to equilibrate the temperature between species without collisions in a magnetospheric plasma. The classical stability analysis in terms of energetic consideration reveals the interchangeable roles of electrons and ions for destabilization depending on their temperatures. Nonlinear gyrokinetic simulations confirm that the higher-temperature destabilizing species gives free energy to heat the other species to achieve the equal temperature state.