EFFECTS OF NONLINEAR ELECTRON DYNAMICS IN A FLUID MODEL OF COLLISIONLESS TRAPPED-ELECTRON MODE TURBULENCE

The role of the electron nonlinearity on saturation levels and particl e transport in collisionless trapped electron mode turbulence is exami ned numerically using a two-dimensional fluid model. It is found that the removal of the electron nonlinearity results in an order of magnit ude increase in fluctuation and particle transport levels. In addition , the qualitative behavior of the saturated state changes distinctly, including a decrease in RMS wave number in both cross-field directions , deviations from isotropy, changes in transport scalings, and changes in the spectral flow of energy. These results indicate that the elect ron nonlinearity is responsible for an efficient transfer of internal energy to small dissipation scales, thus resulting in lower fluctuatio n levels than predicted by ion mode coupling alone. The electron nonli nearity also decreases the phase angle between the density and potenti al leading to a decrease in the driving source. These results undersco re the importance of the cross-correlation on saturation and demonstra te that numerical or theoretical use of ''idelta'' models to describe weakly collisional or collisionless trapped-electron mode turbulence i s not appropriate.