Instability due to axial shear and surface impedance

The stability of plasma flow in the scrape-off layer of a tokamak, taking into account the surface sheath impedance and the axial shear in the E x B flow is analyzed. An interesting stability criterion arises in the limit that end plates are sufficiently far apart, so that stability can be analyzed when the plasma is taken to interact with a single end plate. It is conjectured that the stability of this problem may be of relevance to establishing H-mode conditions in diverted tokamak plasmas