Surface composition of advanced W materials during high-flux plasma exposure*

Increasingly, advanced tungsten materials containing dispersoid particles (e.g. TiO₂, TaC, Ni) or dopants (Re, K) are recieving consideration as plasma-facing materials for MFE. The effect of shallowly implanted D, He, and N on sputtering and surface-to-bulk transport of impurity species is not yet well understood, but nevertheless can have a significant influence on the composition of the outer-most atomic layers presented to the plasma. In addition, these new materials can have much more complex surface chemistry than pure polycrystalline tungsten. In this study, we rely on a combination surface sensitivie diagnostics, including in-situ low energy ion beam analysis, XPS, and temperature-programmed desorption to decipher these processes. We exposed W-Re, W-Ni, and W-TiO₂ specimens to beams of atomic hydrogen at thermal energies for studies of hydrogen chemisorption, as well as high-flux D₂⁺ plasmas seeded with He and N. Our measurements, obtained at temperatures ranging between 100 - 850 °C, show considerable surface-to-bulk transport mediated by He and N plasma exposure. The concentration and distribution of the implanted N was also found to depend strongly on temperature up to a depth 50 nm depth. As part of this work, we also demonstrate a novel ion time-of-flight (TOF) spectrometer for high-resolution depth profiling that allows for surface composition measurements (including D surface concentration) at elevated pressures (up to 5×10^-2 Pa) during low-flux particle bombardment.