Three-Dimensional Velocity Diffusion in Two-Stream Turbulence

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Abstract
Thr turbulent state initiated by the electron-beam-ion two-stream instability is investigated. The spectrum of fluctuations is concentrated on a Cherenkov cone with a single modulus of phase velocity, azimuthally symmetric around the beam axis. The associated diffusion in velocity space occurs mainly on the surface of a double cone, complementary to the Cherenkov emission cone. This model is supported by an experiment in which the three-dimensional diffusion coeffient is measured with use of space-time correlation functions.