Wiktionary
diocotron instability
n. (context physics English) A plasma instability created by two sheets of charge slipping past each other, in which energy is dissipated in the form of two surface waves propagate in opposite directions, one flowing over the other.
Wikipedia
Diocotron instability
A diocotron instability is a plasma instability created by two sheets of charge slipping past each other. Energy is dissipated in the form of two surface waves propagating in opposite directions, with one flowing over the other. This instability is the plasma analog of the Kelvin-Helmholtz instability in fluid mechanics.