Instability driven by sheath boundary conditions and limited to divertor legs

An instability driven by electron temperature gradient in combination with sheath boundary condition at the divertor plate is considered. A mode localized between the divertor plate and the X point is found. The further propagation of the mode is terminated by a strong shear near the X point. "Heuristic" boundary condition at the control surface situated somewhat below the X point is suggested. The mode manifests a strong dependence on the radial tilt of the divertor plate, thereby providing some degree of control over the plasma transport in the divertor leg. Estimates of the diffusion coefficient show that it may reach the Bohm value.