  Microturbulence in magnetic confined plasmas contributes to energy exchange
between particles of different species as well as the particle and heat fluxes.
Although the effect of turbulent energy exchange has not been considered
significant in previous studies, it is anticipated to have a greater impact
than collisional energy exchange in low collisional plasmas such as those in
future fusion reactors. In this study, gyrokinetic simulations are performed to
evaluate the energy exchange in ion temperature gradient (ITG) turbulence. The
energy exchange due to the ITG turbulence mainly consists of the cooling of
ions in the $\nabla B$-curvature drift motion and the heating of electrons
streaming along a field line. It is found that the ITG turbulence transfers
energy from ions to electrons regardless of whether the ions or electrons are
hotter, which is in marked contrast to the energy transfer by Coulomb
collisions. This implies that the ITG turbulence should be suppressed from the
viewpoint of sustaining the high ion temperature required for fusion reactions
since it prevents energy transfer from alpha-heated electrons to ions as well
as enhancing ion heat transport toward the outside of the reactor. Furthermore,
linear and nonlinear simulation analyses confirm the feasibility of quasilinear
modeling for predicting the turbulent energy exchange in addition to the
particle and heat fluxes.
