Nonlinear Saturation of the Collisional Trapped-Particle Instability

The detrapping effects of fluctuating electrostatic potentials on trapped particles in a Tokamak geometry are investigated. It is shown that nonlinear detrapping saturates the collisional trapped-particle instability at a fluctuating potential $\varphi$ such that $e\varphi \ll \epsilon T$, where $\epsilon$ is the inverse aspect ratio.