Surface morphology changes observed in dispersion-strengthened tungsten alloys exposed to L- and H-mode plasmas in the DIII-D tokamak

Dispersion-strengthened tungsten alloys are being investigated as candidate PFC materials due to their enhanced thermomechanical properties compared to pure tungsten. Samples of W-1.1 wt.% TiC, W-1.1 wt.% TaC, and W-1.1 wt.% ZrC were exposed to DIII-D divertor plasmas with the DiMES exposure probe to measure the impact of dispersoids on D retention, material sputtering and surface morphology. Scanning electron microscopy (SEM) analysis of the samples indicates that exposure to H-mode plasmas resulted in a higher density and size of blister-like surface features (up to ~10s µm) than exposure to L-mode plasmas (as small as ~150-200 nm). The H-mode plasmas had an edge localized mode (ELM) period of 10-20 ms, particle flux of ~4x10²¹ m^-2s^-1 and total fluence of ~1.6x10²³ m^-2 at the probe location, and the L-mode plasmas had a particle flux of ~7x10²¹ m^-2s^-1 and total fluence of ~1.2x10²³ m^-2. Graphite deposits were also observed in SEM micrographs; their presence will be further explored with energy-dispersive spectroscopy. To measure the erosion yield of tungsten and the second phase dispersoids, spectroscopy data was collected using visible emission spectroscopy for the W-I, Ti-I, Zr-I, and Ti-I spectral lines on each individual sample, the results of which will be presented.