Collisionless trapped-electron-mode turbulence and transport in fluid descriptions

A study of particle and electron heat transport in tokamaks due to trapped-electron-mode (TEM) turbulence is presented. The study is based on the Weiland fluid model for ion-temperature-gradient (ITG) modes and TEMs, complemented and compared with a trapped electron fluid treatment which retains contributions from the weakly trapped electrons. The dependence of the fluid transport coefficients on magnetic shear and other plasma parameters is discussed and compared with results obtained from nonlinear gyrokinetic simulations. Inward (pinch) flows of particles and heat, previously reported for the coupled ITG-TEM system, are also found in the TEM dominated regime. (authors)