Transport from Overlapping Electron and Ion Driftwave Instabilities

The electron temperature gradient (ETG) mode is a likely contributor to electron thermal transport in tokamaks. The ETG modes are dominantly unstable for poloidal wavelengths shorter than the ion gyroradius (high-k) where the ion response is abiabatic. Thus, they do not directly produce ion thermal or momentum transport or particle transport. Two potential mechanisms whereby ETG modes could produce transport in these channels are explored in this paper: a nonlinear coupling between high-k ETG modes and ions at low-k and a direct coupling when ETG modes and ion temperature gradient (ITG) modes are unstable in overlapping wavenumber ranges. It will be shown that the particle and momentum transport required to match experiment is small compared to the ETG driven electron thermal transport. Even quasilinearly ETG modes can produce ion transport if the ITG and ETG modes are both unstable at low-k. The implications of this for transport will be explored at the quasilinear level. A new gyro-Landau-fluid (GLF) closure model has been constructed in order to build a transport model which can include the coupling between electron and ion modes including trapped particles. The first growth rate spectra from this model will be shown to give an accurate approximation to the kinetic linear growth rates of drift-ballooning modes in tokamaks. I. Transport Within a Transport Barrier