It has been shown in an earlier paper lsqb;Phys. Fluids B5, 344 (1993)rsqb; that the ion flow speed of a plasma can be much smaller than theEtimes;Bspeed in a strongly doublehyphen;sheared electric field. In this paper, the stability of the plasma is investigated. It is found that a new instability, driven by the difference between the ion and electron flow speed, occurs and may dominate the Kelvinndash;Helmholtz (KH) instability in a nonuniform plasma. This new instability has a driving mechanism similar to that of the Simonndash;Hoh instability and is thus called the collisionless Simonndash;Hoh (CSH) instability. When the CSH instability dominates, the plasma does not become more unstable as the electric field is increased, in contrast to scenarios where the KH instability is dominant.
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