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

• The influence of ammonia on the electron density and temperature in a high-density cascaded arc plasma has been studied by laser Thomson scattering. • The introduction of a small amount of ammonia gives rise to the dramatic decrease of electron density, electron temperature, local static plasma pressure and ion flux. • The results strongly suggest that the NH 3 seeding could be much efficiently to regulate the electron density and electron temperature compared with the N 2 seeding. In this work, the influences of ammonia (NH 3 ) seeding on the electron density ( n e ) and electron temperature ( T e ) in a high-density cascaded arc argon plasma have been investigated by laser Thomson scattering. As NH 3 seeding ratio increases from 0% to 2%, n e significantly decreases from 5×10 19 m -3 to 2×10 18 m -3 and T e 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 n e 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 T e . Both the drops in n e and T e cause the reduction of local static plasma pressure and ion flux. The findings strongly suggest that NH 3 gas could be a much effective impurity for achieving the detached-plasma.