LINEAR AND NON-LINEAR THEORY OF BALLOONING TRAPPED ELECTRON MODE

The linear and nonlinear theories of the trapped electron mode are developed in the limit where the modes overlap many rational surfaces. In cases where shear stabilization is annihilated by toroidal coupling, it is found that the radial width of the mode increases with increasing level of turbulence until ion Landau damping balances the destabilizing effect of trapped electrons. Knowledge of the turbulence level enables the evaluation of the anomalous particle and energy transport. The diffusion coefficient scales with temperature, magnetic field, and density as the superbanana diffusion coefficient due to field asymmetries. Radial localization of the destabilizing trapped electron term caused by the difference between the pitch of the magnetic field and that of the mode results in a reduction of the linear growth rate of order Δ/Xt, where Δ is the spacing between rational surfaces and Xt is the radial wavelength. © 1979 American Institute of Physics.