NONLINEAR ION-MIXING-MODE PARTICLE-TRANSPORT IN THE DISSIPATIVE TRAPPED ELECTRON REGIME

The nonlinear particle transport arising from the convection of nonadiabatic electron density by ion-temperature-gradient-driven turbulence (i.e., ion-mixing mode particle transport) is examined for trapped electron collisionality regimes. The renormalized dissipative nonadiabatic trapped electron phase-space density response is derived and used, along with an ansatz for the turbulently broadened frequency spectrum, to calculate the nonlinear particle flux. In the lower-temperature end of this regime, trapped electrons are collisional and all components of the quasilinear particle flux are outward (i.e., in the direction of the gradients). Nonlinear effects can alter the phase between the nonadiabatic trapped electron phase-space density and the electrostatic potential, producing inward components in the particle flux. Specifically, both turbulent shifting of the peak of the frequency spectrum and nonlinear source terms in the trapped electron response can give rise to inward components. However, in the dissipative regime these terms are small, and the trapped electron response remains dominantly laminar. When the trapped electrons are collisionless, there is a temperature threshold above which the electron-temperature-gradient-driven component of the quasilinear particle flux changes sip and becomes inward. For finite-amplitude turbulence, however, turbulent broadening of both the electron collisional resonance and the frequency spectrum removes this threshold, and the temperature-gradient-driven component remains outward.