Emission Rates in ASTRAL Argon Plasmas.

Relative Emission rates measured in 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 are compared to theoretical predictions. A spectrometer which features a 0.33 m Criss-Cross Scanning monochromator and a CCD camera is used for this study. ASTRAL produces bright intense Ar plasmas with the following parameters: n$_{e}$ = 10$^{12}$ to 10$^{13}$ cm$^{-3}$ and T$_{e}$ = 2 to 10 eV. A rf compensated Langmuir probe is used to measure T$_{e}$ and n$_{e}$. In a first series of experiment Ar I, Ar II and Ar III transitions are monitored as a function of plasma density and this for constant electron temperature. In the second series of experiments, the same transitions are observed as a function of T$_{e}$ while n$_{e}$ is this time kept constant. Observations revealed that T$_{e}$ is by far the most significant parameter affecting the emission rate coefficients in the ASTRAL plasma. The spectroscopy measurements are compared with spectral modeling from the ADAS suite of codes.~ Our collisional-radiative formalism assumes that the excited levels are in quasi-static equilibrium with the ground and metastable populations.~ We use existing standard R-matrix electron-impact excitation data in our modeling, and assess this dataset against the results from a new R-matrix with pseudo-states calculation.