Direct time-resolved observation of tungsten nanostructured growth due to helium plasma exposure

Abstract

Determination of the mechanisms underlying the growth of tungsten fuzz is an important step towards mitigation of fuzz formation. Nanostructured tungsten was produced on resistively heated tungsten wires in a helicon plasma source (maximum flux of 2.5 × 10 21 m −2 s −1). Asymmetry in the setup allows for investigation of temperature and flux effects in a single sample. An effort at elucidating the mechanism of formation was made by inspecting SEM micrographs of the nanostructured tungsten at successive fluence steps of helium ions up to a fluence of 1 × 10 27 m −2. To create these micrographs a single tungsten sample was exposed to the plasma, removed and inspected with an SEM, and replaced into the plasma. The tungsten surface was marked in several locations so that each micrograph is centred within 200 nm of each previous micrograph. Pitting of the surface (diameter 9.5 ± 2.3 nm, fluence (5 ± 2)×10 25 m −2) followed by surface roughening (fluence (9 ± 2) × 10 25 m −2) and tendril formation (diameter 30 ± 10 nm, fluence (2 ± 1) × 10 26 m −2) is observed, providing evidence of bubble bursting as the mechanism for seeding the growth of the tungsten fuzz.

Temperature dependence of underdense nanostructure formation in tungsten under helium irradiation

“…The width of the simulation box (X dimension) was taken as large as the expected size of the tendrils that will be formed (30±10 nm, as reported experimentally in Ref. [46]). The depth of the box (20 nm) allows simulating the migration of He ions (for an implantation depth of ~1.3 nm as calculated by SRIM, see below).…”

Grain orientations and grain boundaries in tungsten nonotendril fuzz grown under divertor-like conditions

“…The present understanding of nanostructure formation is primarily informed by molecular dynamics (MD) or other theory approaches [9][10][11][12][13][14][15][16][17][18], with relatively limited (although valuable) experimental information [5,6,8,[19][20][21]. Still poorly defined is how fuzz transitions from the short incipient state of early growth -well-studied by MD -into the long and stably-growing state during later growth.…”

Enhanced effect of a plasma‐irradiated titanium substrate on the photocatalytic activity of a TiO2 film

“…The most representative morphology is presented in Figure for all samples exposed to the He plasma. As the incidence energy increases from 79 to 169 eV, the morphology transits from spherical particles to valleys of “webs” and eventually to huge hills; morphologies appeared to be bubble‐driven like palladium and tungsten from previous work. Comparing (v) and (vi), as the fluence doubles, sputtering effects started dominating, eliminating the porous structures.…”