Space-time structure of ion beam-plasma turbulence

Abstract

The turbulence excited by an ion beam penetrating an unmagnetized plasma is investigated. One-dimensional linear kinetic theory predicts the ion acoustic mode to be driven unstable when the beam velocity vb ranges from cs to 2cs. Numerical calculations are reported for the three dimensional problem, in which attention is given to unstable waves. The direction of propagation, the phase velocities, and the growth rate contours in the (k∥, k⊥) plane, are given as a function of vb. This instability is created in a double plasma device, and investigated by means of space and time correlations. Turbulence is excited, consisting of modes propagating at a phase velocity which agrees with theory. As vb increases, an abrupt transition from one-dimensional to three-dimensional structure occurs as expected.