Visible emission spectroscopy of electron beam produced rare gas plasmas

Visible emission spectroscopy (380 nm - 650 nm) has been performed on neon, argon, krypton and xenon plasmas produced by an intense, long pulse, electron beam (300 ns pulse width, 1 kA peak current, and 300 kV peak voltage). The visible light was viewed axially to the electron beam and imaged onto the entrance slit of an 0.275 m spectrograph, coupled to an optical multichannel analyzer (OMA). The OMA was gated with pulse widths ranging from 50 ns to 500 ns. The pressures examined ranged from 1 torr to 1 atmosphere. Singly ionized lines dominated the spectra in all cases and the spectra were found to change very little as a function of time during the current pulse. The temperature of the plasmas were about 1 eV as determined from Atomic Boltzmann plots. A couple of intense lines were observed for each gas, whose intensity did not match that which would be expected for a 1 eV plasma. These lines originated from highly excited states, relative to the lines used to determine the plasma temperature. This enhancement can be explained in terms of a recent theory which predicts that the presence of fast particles can significantly enhance allowed radiative transitions