Interaction of a high-current relativistic electron beam with a dense plasma

Abstract

Laser-scattering and line-emission measurements of a plasma heated by an intense electron beam are reported. The e-beam’s parameters are 350 kV and 36 kA for 100 ns, and the beam density is either 6×1011 or 5×1012 cm−3 for injection into a plasma and into a neutral gas, respectively. The plasma number density is varied from 5×1013 to 3×1015 cm−3, and the initial temperature is less than 10 eV. There is no external magnetic field. When there is a large net current in the beam-plasma system, as there is for injection into a neutral gas, the dominant energy transfer is from the beam to the ions through a radially outward plasma acceleration in the Hall electric field jp×B/npe. The laser-scattering data is consistent with large azimuthal and radial plasma currents which are presumed to be driven by the azimuthal asymmetry of the Hall electric field. When the beam is injected into a preformed plasma, the net current and the effects of the Hall field are sufficiently small to allow the electron heating mechanisms to be studied. The final electron energy density is consistent with heating via anomalous collisions arising from the ion-acoustic instability in addition to classical collisions. Furthermore, the expected energy transfer via the electron-electron two-stream instability is not observed.