Plasma structures of Ar-H₂ mixed gas tungsten arcs determined by spectroscopic measurements

Summary

A previous paper describes an investigation of different temperature distributions in Ar-H₂ mixed gas tungsten arcs evaluated by means of argon atom line (Ar I), hydrogen atom line (H I), and. ionised argon line (Ar II) intensities determined by emission spectroscopic measurements. When Ar-H₂ mixed gas tungsten arcs are evaluated by these conventional spectroscopic methods, however, differences arise depending on the analytical method adopted, giving results which are either higher or lower than those of argon arcs.

To find a solution to these inconsistent results, a new spectroscopic method (called the Ar I-H I two-line intensity correlation method) has been developed to estimate the correlation between Ar I and H I intensities on the assumption of local thermodynamic equilibrium (LTE) and a heterogeneous plasma gas composition.

The temperature distribution determined by the Ar I-H I two-line intensity correlation method shows good agreement with that determined by the previously reported Ar I-Ar II correlation method. This shows that consistent temperature distributions can be obtained from Ar I, Ar II, and H I intensities.

The electron density distributions were also determined without the assumption of LTE by both Stark's broadening method for the hydrogen atom line H_β and the infrared emission plasma diagnostics method. These results show good agreement with the electron density distributions calculated by Saha's relations for the local plasma gas composition and temperature determined by the Ar I-H I two-line intensity correlation method.

The results suggest that the spectroscopic analysis of Ar-H₂ mixed gas tungsten arc plasma on the assumption of LTE is a valid approach and that the hydrogen gas concentrated near the cathode and the temperatures in the plasma region as a whole are much lower than the temperatures in a pure argon gas arc.