Nonlinear saturation of single-mode trapped electron instability

Abstract

The trapped electron instability, like other types of drift waves, may appear as a single mode in many linear plasma devices. Recognizing the significant variation of density gradient over the mode localization region, a nonlocal linear analysis in slab model yields eigenfunctions for Weber-like equations. Using three-wave, nonresonant, two-dimensional mode coupling based on these Weber-like eigenfunctions, two mode-coupling equations for the fundamental and higher-order radial harmonics are derived. The solution of these coupled equations yields the nonlinear saturation level of the unstable mode. Mode coupling to the damped higher-order radial modes is the principal physical saturation mechanism of the unstable fundamental mode.