Ion-electron two-stream instability in EBIS ion sources

We study the ion-electron two-stream instability, believed to limit the efficiency of EBIS ion sources. We find that it cannot be stabilized by electron kinetic effects, so that it unavoidably leads to heating of the ions. The latter thus spread radially beyond the electron beam radius, explaining the reduced efficiency of the sources. This finally suppresses the instability only when the efficiency is reduced to a few percents of its nominal value.