Cross Comparison on DIII-D of Experimental Techniques for Measuring ${\bf n_e}$ and ${\bf T_e}$ in Detached Divertor Plasmas

Spectroscopy of high-n, Balmer line transitions provides a means of measuring $n_e$ and $T_e$ in recombining plasmas [1]. The relative intensities of Rydberg series lines near the ionization limit are a sensitive diagnostic of $T_e$ for $T_e <\,$1~eV. Stark broadening of these same lines provides a measure of local $n_e$ and with less accuracy of $T_e$. Predictions from Balmer line spectroscopy are compared with those from divertor Thomson scattering to evaluate the accuracy of different theoretical models of line broadening [2,3]. In particular, the detailed dependence of line width on principal quantum number is used to distinguish which line-broadenign model best accords with experiment.\par \vskip6pt \noindent [1]~J.\ Terry, Phys.\ Plasmas {\bf 5}, 3373 (1998).\par \noindent [2]~H.\ Griem Spectral Line Broadening by Plasmas, Academic Press, New York (1974).\par \noindent [3]~E.\ Oks Stark Broadening of Hydrogen and Hydrogenlike Spectral Lines in Plasmas: The Physical Insight, Alpha Science International, Oxford, UK (2006).