Experimental Observation of Nonlinear Wave-Particle Interactions in a Weak Cold Beam-Plasma System

Abstract
Nonlinear evolution of a beam-plasma instability has been investigated by direct measurements on the energy distribution of beam electrons and the field intensity of an externally driven electrostatic wave. The initial exponential growth of the excited single wave is halted when the wave traps the electrons and rotates them in phase space. At the phase of spatial bunching of the beam, its harmonics are observed to have maximum values. The results agree with those predicted by a single wave model.