Ultraviolet measurements of tungsten gross-erosion and re-deposition rates during ELMs in the DIII-D tokamak

Ultraviolet (UV) spectroscopic measurements of tungsten (W) gross-erosion and re-deposition performed during Edge Localized Modes (ELMs) in the DIII-D tokamak show ~10 times larger erosion levels during ELMs than during inter-ELM plasma phases. In attached divertor plasmas conditions with large Type I ELMs, tungsten erosion due to ELMs dominates the total W source. W gross erosion was measured from neutral W emission lines (W I) in the UV wavelength range (250-270 nm) combined with ionization/photon (S/XB) coefficients previously obtained from DIII-D experiments. S/XBs used for W I emission lines have larger values than predicted by collisional radiative models. A 5 cm diameter W sample installed in the Divertor Material Evaluation System (DiMES), in the DIII-D lower divertor, was exposed to low frequency ELMs (15 – 20 Hz). Gross-erosion rates on the order of ~10¹⁶ atoms cm^-2 s^-1 were observed during ELMs. UV measurements of W gross-erosion have been benchmarked with a visible W I emission line at 400.88 nm. W re-deposition fractions of ~75% were determined from singly-ionized tungsten emission lines (W II) showing no appreciable variation between ELM and inter-ELM phases.

*Work supported by the Department of Energy under Award Numbers DE-SC0015877, DE-FG02-00ER54610 and DE-FC02-04R54698.