Damping mechanisms for ion plasma waves excited by a fast ion beam

It is shown, for the first time, that the ion waves excited by a fast ion beam are damped primarily as a result of the finite lifetime of the plasma ions. The spatial damping rate and dispersion calculated for the waves for this mechansim agree well with some new experimental results. The effect of the charge exchange of the beam ions on the beam instability has also been studied. It is shown theoretically and experimentally that at gas pressures which are not to high the charge exchange initially reduces the spatial growth rate along the beam axis and then causes a change in its sign. At high gas pressures these damping mechanisms completely suppress the instability