Enhanced fuzzy tungsten growth in the presence of tungsten deposition



McCarthy, Patrick, Hwangbo, Dogyun, Bilton, Matt ORCID: 0000-0002-0475-2942, Kajita, Shin and Bradley, James W
(2020) Enhanced fuzzy tungsten growth in the presence of tungsten deposition. Nuclear Fusion, 60.

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Abstract

Using a magnetron sputtering device operating in helium, fibre-form 'fuzz' has been grown on tungsten samples in the presence of a significant auxiliary source of depositing tungsten. In this system, fuzzy tungsten was grown over a range of helium ion fluences, , sample temperatures and helium ion energies, but with operator control over the tungsten atom-to-helium ion arrival rate ratio at the sample (from 0.003 to 0.009). In the presence of tungsten deposition, it appears that the fuzz growth has two distinct stages: at low to intermediate helium ion fluence the fuzzy layer thickness follows the expected diffusive law augmented by approximately the 'effective' thin film thickness of deposited tungsten; at high fluences the fuzz thickness increases very steeply with . These observations are explained through the increase in the porosity of the fuzzy layer as it reaches thicknesses larger than ~1 m. It was observed that during the second phase of fuzz growth the thickness was highly dependent on both the sample temperature and the tungsten atom-to-helium ion arrival rate ratio. For the same helium ion exposure, an increase in the sample temperature from 1050 to 1150 K lead to a six-fold increase in the fuzzy layer thickness, whilst increasing the tungsten atom-to-helium ion arrival rate ratio over the full range produced a two-fold increase in the thickness. Microscopy and electron diffraction studies of the grown structures show clearly helium bubbles within polycrystalline tendrils.

Item Type: Article
Depositing User: Symplectic Admin
Date Deposited: 07 Jan 2020 10:24
Last Modified: 01 Sep 2022 07:18
DOI: 10.1088/1741-4326/ab6060
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3069518