Spectroscopy Study of Ar + CO$_{2}$ Plasmas in ASTRAL.

A spectroscopy study of the ASTRAL (\textbf{A}uburn \textbf{S}teady s\textbf{T}ate \textbf{R}esearch f\textbf{A}ci\textbf{L}ity) helicon plasma source running Ar + CO$_{2}$ gas mix is presented. ASTRAL produces Ar plasmas: n$_{e}$ = 10$^{10}$ to 10$^{13}$ cm$^{-3}$, T$_{e}$ = 2 to 10 eV and T$_{i}$ = 0.03 to 0.5 eV. A series of 7 large coils produce an axial magnetic field up to 1.3 kGauss. A fractional helix antenna is used to introduce rf power up to 2 kWatt. A spectrometer which features a 0.33 m Criss-Cross monochromator and a CCD camera is used for this study. Very different plasmas are produced following the relative importance of CO$_{2}$ in the gas mixture. At low CO$_{2}$ concentration, the plasmas are similar to those obtained with pure Ar with weak CO$_{2}$, CO$_{2}^{+}$, CO and CO$^{+}$ bands. The usual blue plasma core associated with intense Ar II transitions is observed with however a significant white glow coming from the outer plasma regions. At higher CO$_{2}$ concentration, the plasma becomes essentially molecular and can be described as an intense white plasma column. Molecular dissociative processes associated with the production of strong C and O atomic lines are observed under specific plasma conditions. The atomic spectral lines are compared with ADAS modeling results. This study indicates the possible advantages of using a helicon source to control the CO$_{2}$ plasma chemistry for industrial applications.