A kinetic theory of trapped electron driven drift wave turbulence in a sheared magnetic field
Abstract
A kinetic theory of collisionless and dissipative trapped electron driven drift wave turbulence in a sheared magnetic field is presented. Weak turbulence theory is employed to calculate the nonlinear electron and ion responses and to derive a wave kinetic equation that determines the nonlinear evolution of trapped electron mode turbulence. Saturated fluctuation spectrum is calculated using the condition of nonlinear saturation. The turbulent transport coefficients are in turn calculated using saturated fluctuation spectrum. Due to the disparity in the three different radial scale lengths of the slab-like eigenmode: Delta trapped electron layer width, x sub t (turning point width) and x sub i (Landau damping point), Delta less than x sub t less than x sub i, we find that ion Compton scattering rather than trapped electron Compton scattering is the dominant nonlinear saturation mechanism. Ion Compton scattering transfers wave energy from short to long wavelengths where the wave energy is shear damped. As a consequence, a saturated fluctuation spectrum (vert bar phi vert bar sup 2 k sub theta) approximately k sub theta sup minus alpha alpha = 2 and 3 for the dissipative and collisionless regime, respectively occurs for k sub theta rho sub s less than 1 and is heavily damped for k sub theta rho sub s greater than 1. The predicted fluctuation level and transport coefficients are well below the mixing length estimate. This is due to the contribution of radial wavenumbers x sub t sup minus 1 less than k sub r le rho sub i sup minus 1 to the nonlinear couplings, the effect of radial localization of trapped electron response to a layer of width, Delta, and the weak turbulence factor l angle gamma sub e sup l/omega sub rvec kappa r angle sub rvec k less than 1, which enters the saturation level.
- Publication:
-
Unknown
- Pub Date:
- September 1990
- Bibcode:
- 1990ktte.rept.....G
- Keywords:
-
- Compton Effect;
- Ion Scattering;
- Kinetic Theory;
- Kinetics;
- Plasma Waves;
- Trapped Particles;
- Turbulence;
- Electrons;
- Magnetic Fields;
- Physics (General)