Observation of the significant reductions of electron density and electron temperature in a cascaded arc high density argon plasma with ammonia seeding comparing with nitrogen seeding by laser Thomson scattering approach

Abstract

In this work, the influences of ammonia (NH3) seeding on the electron density (ne) and electron temperature (Te) in a high-density cascaded arc argon plasma have been investigated by laser Thomson scattering. As NH3 seeding ratio increases from 0% to 2%, ne significantly decreases from 5 × 1019 m−3 to 2 × 1018 m−3 and Te changes from 0.41 eV to 0.34 eV. The investigations show that the reductions of electron density and electron temperature with ammonia seeding are much significant comparing with nitrogen seeding. The reduction of ne is attributed to the dissociated recombination reactions between electrons and molecular ions formed via the charge exchange reactions. The electron-impact vibrational excitation to molecules leads to the drop in Te. Both the drops in ne and Te cause the reduction of local static plasma pressure and ion flux. The findings strongly suggest that NH3 gas could be a much effective impurity for achieving the detached-plasma.

Keywords

• Cascaded arc plasma
• Detached-plasma
• Nitrogen–hydrogen compounds
• Electron density
• Electron temperature
• Laser Thomson scattering