High-resolution ultraviolet spectroscopy of tungsten and tantalum emission for improved erosion measurements

Characterizing erosion of Plasma Facing Components (PFC) in magnetically confined experiments is necessary for understanding edge impurity dynamics and PFC lifespan in future fusion devices. A spectroscopic technique for temporally determining PFC erosion relates observed spectral line intensities to material influx via atomic physics coefficients (S/XB). However, failing to sufficiently resolve measured spectral lines due to impurity line blending, pressure broadening, and Zeeman and Stark splitting may lead to incorrect erosion estimations. A 1.3 meter focal length spectrometer is being optimized for high-resolution (8 pm) ultraviolet (200-400 nm) spectral measurements in the Compact Toroidal Hybrid (CTH) device. W and Ta samples are introduced into the plasma at varying depths with simultaneous Langmuir probe measurements of electron parameters. Comparisons of highly-resolved W spectra to recently computed atomic data for neutral W and W+ are made using the ColRadPy collisional radiative suite of codes to account for potential broadening mechanisms. First spectroscopic measurements of Ta emission in CTH are presented along with identifications of Ta spectral lines for potential benefit to erosion measurements.