Spectroscopic Characterization of Low-Temperature Plasma Produced by Intense Electron Beams*

The low-temperature plasma produced by the electron beam emitted from a Febetron pulsed-power generator is being characterized spectroscopically. The generator located at the Naval Research Laboratory produces a peak voltage of 80 kV, peak current of 4 kA with a pulse width of 100 ns. This beam passes through a thin anode foil into a chamber filled with various background gases at pressures between 10 mTorr and 10 Torr. Emission spectra from the near-UV to visible (300-650 nm) of the beam-generated plasma are measured using a time-integrated survey spectrometer, a 0.5 m focal length mid-resolution spectrometer, and a sub-angstrom resolution 1.3 m focal length spectrometer. The 1.3 m spectrometer takes multiple simultaneous spectral measurements per pulse, enabling measurements of spatial variations of the plasma spectra through a 7-fiber input array. Imaging of the spectra is conducted by a 2D intensified gated CCD over small time increments to analyze the time-resolved evolution of the emissions. These measurements provide data on the population dynamics of N₂ rotational states, which provides a useful validation dataset for modeling performed using recently computed state-to-state cross sections for rotational states of neutral and ionized N₂.