Simulation of the Beam‐Plasma Instability in a Finite‐Length System

Abstract

The electron and ion beam‐plasma instabilities in a one‐dimensional finite‐length system are studied by computer simulation methods using the discrete charge‐sheet model. The results obtained using a one‐component model indicate that the region of highly concentrated oscillation energy (due to a beam‐plasma instability) near the beam entrance plane shrinks with time to a limiting value and then expands to form a stationary electric‐field distribution. The frequency spectrum analysis of the electric field shows that only the first few harmonics of electron plasma oscillations have been excited and only these harmonics have amplitudes significantly above the noise level in the nonlinear region. In the experiment on the ion‐beam interaction with a plasma, the plasma electrons and ions achieve greater heating in comparison with the heating resulting from the interaction between an electron beam and a plasma, because the heavier ion mass yields a larger energy source, a low rate of decrease of the mean ion‐beam speed, and reduced thermal spreading of the beam particles. The excited electron plasma oscillations are found to dissipate into ion‐density fluctuations whenever the amplitude exceeds some threshold value.