Ar + CO$_{2}$ and He + CO$_{2}$ Plasmas in ASTRAL

Spectroscopy study of the ASTRAL helicon plasma source running Ar + CO$_{2}$ and He + CO$_{2}$ gas mixes is presented. ASTRAL produces plasmas with the following parameters: n$_{e}$ = 10$^{10}$ - 10$^{13}$ cm$^{-3}$, T$_{e}$ = 2 - 10 eV and T$_{i}$ = 0.03 - 0.5 eV, B-field $\le $ 1.3 kGauss, rf power $\le $ 2 kWatt. A 0.33 m scanning monochromator is used for this study. Using Ar + CO$_{2}$ gas mixes, very different plasmas are observed as the concentration of CO$_{2}$ is changed. At low CO$_{2}$ concentration, the bluish plasma is essentially atomic and argon transitions dominate the spectra. Weak C I and O I lines are present in the 750 - 1000 nm range. At higher CO$_{2}$ concentration, the plasma becomes essentially molecular and is characterized by intense, white plasma columns. Here, spectra are filled with molecular bands (CO$_{2}$, CO$_{2}^{+}$, CO and CO$^{+})$. Limited molecular dissociative excitation processes associated with the production of C I and O I emission are also observed. On the other hand, He + CO$_{2}$ plasmas are different. Here, rf matches are only possible at low CO$_{2 }$concentration. Under these conditions, the spectra are characterized by strong C I and O I transitions with little or no molecular bands. Strong dissociative processes observed in these plasmas can be link to the high T$_{e}$ associated with He plasmas. An analysis of the spectra with possible scientific and industrial applications will be presented.