Spectroscopically diagnosing gross tungsten erosion using time-dependent collisional radiative modeling

Improved diagnosis of tungsten gross erosion can be achieved with improved predictions of atomic rate coefficients and time-dependent collisional radiative (CR) modeling in combination with high-resolution ultraviolet spectroscopy. A CR model accounting for time-dependent effects due to the inclusion of a magnetic sheath at the plasma boundary is developed. CR coefficients for tungsten erosion measurements can be modified by up to a factor of ten by a sheath at ITER relevant conditions. Comparisons of electron temperature inferred from CR modeling and Langmuir probe measurements are in good agreement for Compact Toroidal Hybrid (CTH) plasmas suggesting the atomic data and CR modeling of neutral tungsten is accurate. Due to the importance of determining the effects of metastable levels on spectroscopy, CR modeling using ColRadPy is employed to analyze the impact of metastable states on tungsten emission and ionization. A technique for measuring non-steady state (time-dependent) metastable populations is presented using W I spectral lines around 260 nm. A high-resolution UV optimized spectrometer has been commissioned on the CTH experiment and the tungsten spectra are compared to modeled spectra using W I R-matrix excitation data.