Plasma heating by injection op relativistic electron beams in neutral gas

We report laser scattering measurements of the electron density of a magnetized plasma produced by a relativistic electron beam (350kV, 50kA, 100ns, 2 cm diameter) injected into neutral hydrogen. Electron number densities of ~5 10¹⁵ cm^-3 corresponding to ≳ 20% ionization and electron temperatures <; 10eV are observed during the late stages of the e-beam pulse. The corresponding electron thermal energy is much smaller than can be expected from the measured resistive heating due to the plasma return current. The measured resistivity appears to be classical. An ion temperature of ~ 100eV is inferred from Doppler broadening of H_α and H_β radiation of charge exchange neutrals. This ion thermal energy is in reasonable agreement with the observed plasma diamagnetism. Soft X-ray measurements put a limit (n_e <; 3.7 10¹⁴ cm^-3, T_e >; 2.6keV) on the electron tail if the energy density in the tail is assumed equal to the plasma diamagnetism.