Universal instability in a plasma sheath

Low-frequency drift waves are considered in a planar sheath of neutral plasma with thickness on the order of the ion gyroradius. An integral eigenmode equation is derived and solved numerically using fast Fourier transforms. The analysis is valid for arbitrary wavenumbers and accounts for shear in the equilibrium magnetic field. It is found that unstable universal drift modes can exist in this strongly localized plasma. In contrast to what has been found previously in connection with weakly inhomogeneous plasmas, it is observed here that shear can have a destabilizing influence. The relevance of this idealized model to experiments is also discussed.