Emission spectroscopy of long pulse relativistic electron-beam-produced argon plasmas

Visible emission spectroscopy of long pulse, relativistic, electron-beam (300 ns, 1 kA, 300 keV) -produced argon plasmas has been performed over a wide pressure range (1–750 Torr). The emission spectra were observed between 350 and 600 nm with a spectrograph coupled to an optical multichannel analyzer, which was gated with pulses of 50 and 500 ns. Singly ionized argon lines were observed at all pressures and all times during the beam current. The relative line intensities for the (4s–4p) transitions fit those described by an equilibrium distribution at approximately 2 eV. The emission lines originating from the higher excited states of (4s′–4p′) and (4s″–4p″) were much larger than expected in a 2-eV plasma, and this enhancement can be attributed to the presence of the beam electrons.