Nonlinear stage of the modulational instability of Langmuir oscillations in a beam-plasma experiment

Abstract Langmuir oscillations with a rather large amplitude, at which a modulational instability is “switched on”, were studied experimentally in a collisionless unmagnetized plasma with an electron beam. In accordance with predictions of a theory advanced by Zakharov, it is shown that, as the instability develops, the region with a strong electric field “collapses” down to about 6 Debye lengths and the field is, then, rapidly attenuated.