Fluid Density Dependence of Electrical Discharges Generated Using Carbon Nanotube as Electrode in Liquid, Supercritical, and Gaseous Nitrogen*

Plasmas in high-density media, including liquids and supercritical fluids (SCFs), have been attracting attention. We have previously reported the successful generation of stable low-voltage discharges in high-density N₂ and Ar using carbon nanotubes as electrodes, which are thought to act as field emitters [1]. In supercritical and liquid N₂, the strong auroral green emission derived from ON₂ excimer was observed, suggesting that the discharge was reactive. However, little is known about the plasma chemistry with CNT electrodes, since no detailed measurements have been made so far. In this study, we discuss the fluid density dependence of optical emissions by taking more than several thousand spectra while continuously varying the density in the range of two to three orders of magnitude from gases, SCFs, and liquids at cryogenic temperatures. With increasing density, the emission intensity of ON₂ initially decreased, but began to increase after ~10²¹ cm⁻³. At high densities, not only the emission intensity but also the emission area was wider, which was clearly different from the density dependence of normal discharges. Further details including spectral broadening and discussion will be presented.

[1] H. Muneoka et al, Plasma Sources Sci. Technol. 28, 075014 (2019).