Energy exchange induced by ITG turbulence in weakly collisional plasmas

In magnetically confined plasmas, turbulence induces energy exchange between electrons and ions as well as particle and heat fluxes[1]. In a previous study [2], the effect of turbulent energy exchange on prediction of plasma density and temperature profiles was investigated under specific conditions and it was found to be negligible. However, a detailed comparison between the turbulent and collisional energy exchanges has not been shown in the case of very high-temperature plasmas such as those in ITER, where the collision frequency is very low. In this work, effects of ion temperature gradient (ITG) turbulence on the energy exchange in tokamak plasmas are quantitatively investigated by the gyrokinetic simulation code GKV[3]. As a result, different properties between collisional and turbulent energy exchanges are revealed. The turbulent energy exchange can dominate over the collisional one at high temperature (low collision frequencies). Also, the turbulent energy transfer can occur in the opposite direction to the collisional one. Coulomb collisions make energy transfer from hotter to colder species. On the other hand, in the ITG turbulence, energy can flow from colder ions to hotter electrons. In addition, to develop the quasilinear model for the turbulent energy exchange, we have found a good correlation between the linear and nonlinear simulation results. [1] H. Sugama et al., Phys. Plasmas, 1996. [2] J. Candy, Phys. Plasmas, 2013.[3] T.-H. Watanabe et al., Nucl. Fusion, 2006.