Evaluation and Implementation of Helium Line Ratio Technique for Measurement of Edge Density and Temperature on DIII-D

The electron density and temperature in the scrape-off layer of DIII-D have been determined in pure helium plasmas by the helium line ratio technique [1] employing spectral line monitors and an intensified fast-framing CCD camera. Both diagnostics viewed the plasma tangentially on the midplane of the vessel. Three visible He I transitions, one triplet (3$^3$S$\rightarrow$2$^3$P) and two singlets (3$^1$D$\rightarrow$2$^1$P and 3$^1$S$\rightarrow$2$^1$P), were measured simultaneously --- along a single spatial chord with the line monitors and over a 2D region of the outer midplane with the intensified camera. Column brightnesses through the emission shell recorded with the camera were Abel-inverted to yield local intensities with a spatial resolution of a few millimeters. The electron densities and temperatures deduced by the helium line ratio method are compared with results from the Thomson scattering diagnostic on DIII-D.\par \vskip8pt \noindent [1] O.~Schmitz {\em et al.}, Plasma Phys.\ Control.\ Fusion {\bf 50} (2008) 115004.