Theory of electric-field curvature effects on long-wavelength drift wave turbulence

A simple model of long-wavelength drift waves is used to study the way in which a radial electric-field profile influences the growth and saturation of turbulence. For a fixed external field, the effect of curvature (∂2Er/∂r2) dominates that of shear (∂Er/∂r). In the linear regime, both affect the average k∥ at which ion damping occurs: shear by shifting the eigenmode off the resonant surface and curvature by changing the eigenmode width. Curvature damps more efficiently and also shifts the real frequency of the drift wave, changing the instability drive. In the nonlinear regime, radial trapping at large fluctuation levels limits the ability of an external electric-field profile to affect the spatial structure. Changes in damping are now less effective than the feedback between frequency shift and drive. The importance of the frequency shift caused by electric-field curvature in the presence of finite-amplitude fluctuations has been demonstrated by numerical calculations.