The effects of impurity gas seeding on the growth of fuzzy tungsten

McCarthy, Patrick, Hwangbo, Dogyun, Kajita, Shin and Bradley, James W (2021) The effects of impurity gas seeding on the growth of fuzzy tungsten. JOURNAL OF NUCLEAR MATERIALS, 556. p. 153125.

Text McCarthy paper_153125.pdf - Author Accepted Manuscript Download (1MB) | Preview

Abstract

Using the linear plasma device NAGDIS-II operating with gas mixtures of helium (He) and impurity (Ne, N2, Ar), fibre-form nanostructures known as “fuzz” have been grown on tungsten (W) samples. In this system, fuzzy W was grown over a range of sample temperatures and ion fluences (containing He and impurity ion mixtures), but with operator control over the impurity to helium percentage (from 5 – 10%). The ion energies were held constant at 60 eV throughout the experiments. Close inspection of the surface morphologies showed that a variation in fuzzy structure was produced on W surfaces depending on the impurity species used. Specifically, Ne impurity produced cone-like fuzz structures and Ar and N2 caused more random tendril growth. Using a constant fluence of He and impurity ion species, the effective fuzzy layer growth rate is reduced for higher impurity atomic masses and higher concentrations. For 10 % N2 within the He plasma, little fuzz growth was visible on the W surface. Where 7.5 – 10% of Ar was used, fuzz growth was terminated completely. From mass loss measurements the net erosion yields of W surfaces exposed to 95 % He + 5% impurity (Ne or N2) discharges were measured to be lower than bulk W sputtering yields for each impurity species, decreasing sharply with increasing fuzz thickness. Under high ion fluences up to 1027 m−2, steady-state thicknesses of W fuzz were attained due to the combined effect of fuzz growth and sputter erosion caused by the impurity species in the plasma. The measured steady-state thicknesses were found to be consistent with an analytical model developed for the simultaneous growth and erosion of fuzz. SEM imaging showed the presence of larger fuzzy structures, Nano-tendril bundles (NTBs), on surfaces where fuzz grew under the presence of impurity species. The formation of NTBs were characterised in terms of their surface temperature threshold ranges.

Item Type:	Article
Uncontrolled Keywords:	Helium, Tungsten, Fuzzy Tungsten
Divisions:	Faculty of Science and Engineering > School of Electrical Engineering, Electronics and Computer Science
Depositing User:	Symplectic Admin
Date Deposited:	09 Aug 2021 08:05
Last Modified:	18 Jan 2023 21:33
DOI:	10.1016/j.jnucmat.2021.153125
Related URLs:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3132813