Nonlinear Energy Flow in a Beam-Plasma System

The three-dimensional character of the beam-plasma instability is investigated. The true beam-electron distribution function is resolved with a novel directional energy analyzer. The electron plasma waves ($\omega \approx {\omega }_p\gg {\omega }_c$) are observed to develop a large spread in perpendicular wave numbers ($\delta k_{\perp }\approx k_{\parallel }$) and damp in a relatively short distance producing an energetic electron tail on the background distribution. The damping is believed to be due to strong ion fluctuations which produce an anomalous resistivity.