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Baldwin, M. J. (ORCID:0000000163352255)

Publications and source records attributed to Baldwin, M. J. (ORCID:0000000163352255).

13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Deuterium plasma induced preferential erosion in ultra-high temperature ceramics TiB 2 and ZrB 2 *

Abstract Steady-state deuterium plasma exposures were performed on ultra-high temperature ceramics titanium diboride (TiB 2 ) and zirconium diboride (ZrB 2 ) using the PISCES-RF linear plasma device (LPD) as early screening for first wall, plasma-facing applications. Deuterium plasma exposures were performed using 40 eV ion energies at 240, 525, and 800 °C sample temperatures and 90 eV ion energies at 240 °C sample temperatures to analyze TiB 2 and ZrB 2 surface morphology and chemistry evolution behavior. Post-plasma exposure chemistry characterization of the near surface ( < 50 nm) region of the samples all show transition metal enrichment, indicating boron preferential erosion. Transition metal to boron fractions vary with plasma exposure temperature under the 40 eV ion energy; metal enrichment is maximized at 800 °C and then minimized at 525 °C. SEM micrographs of all plasma exposed sample surfaces show no significant or noticeable plasma induced damage from cracking or blistering.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Observation of tantalum deposition and growth on TiB2 and ZrB2 from PISCES-RF deuterium and helium plasma exposures

Deuterium and helium plasma exposures on bulk TiB2 and ZrB2 samples were performed using the PISCES-RF linear plasma device. 40 and 90 eV deuterium ion plasma exposures were performed at 240 and 800 °C sample temperatures, and 80 eV helium ion plasma exposures were performed at 800 °C sample temperatures. Following plasma exposures, it was discovered that two plasma conditions (90 eV deuterium and 80 eV helium at 800 °C) resulted in thick (>200 nm) tantalum-rich (>10 at%) surface features on the targets, presumably from tantalum sourced from a tantalum adapter mask or cap used as part of the target holder. This work aims to characterize these tantalum-rich features and examine the mechanisms of impurity deposition.Plasma-induced surface morphology of the tantalum-rich surface layers depends on plasma properties and target temperature and chemistry. Greater titanium sputtering compared to zirconium resulted in more distinct surface features in the TiB2 samples compared to the ZrB2 samples via increased, prompt deposition onto tantalum surface impurities. There is still uncertainty as to why thick tantalum deposition only occurred under some plasma exposure conditions but not others; it is likely due to tantalum sputtering by a combination of boron molecules from the targets and carbon-impurities in the tantalum mask or targets. Impurity driven surface features are a well-documented phenomena in samples exposed to plasma from linear plasma device facilities—this work confirms the occurrence of this and emphasizes the need for chemistry characterization of isolated post-mortem surface features in plasma-exposed samples.

Nuckols, Lauren↗
DOE OSTI2024

Reply to Comment on ‘Deuterium supersaturated surface layer in tungsten: ion energy dependence’

Abstract We reply to the comment by Li et al (submitted to Nucl. Fusion with this response) on our recent paper Nishijima et al (2023 Nucl. Fusion 63 126003). In this response, we address the existence of an incident ion energy, E i , threshold for the deuterium (D) supersaturated surface layer (DSSL) formation with a newly conducted D plasma exposure experiment at E i ∼ 20 eV. It is also further demonstrated, based on new experiments where the ion flux, fluence, and sample temperature are scanned, that non-kinetic (ballistic) processes play a role in the DSSL formation and growth. In addition, the effect of impurities in our plasma is discussed also with a new analysis of the surface composition made after a D plasma exposure.

Nishijima, D. (ORCID:0000000231194827)↗
DOE OSTI2023

The dependence of tungsten fuzz layer thickness and porosity on tungsten deposition rate and helium ion fluence

Abstract Fuzz formation on a heated tungsten surface in the presence of a helium-containing plasma and tungsten deposition source was investigated. Tungsten samples were exposed at 1123 K to pure helium plasma with ion incident energy of 76 eV, W/He ion flux ratio of ∼ 0.4 × 10 − 4 , and varied helium ion fluence from 0.18 to 3.4 × 10 26 m −2 . Fuzz thickness was measured by cross-sectional scanning electron microscopy to increase from 0.22 to 15 µ m with increasing helium ion fluence. No indication of saturation in fuzz thickness at high fluence was observed, in contrast to fuzz produced on a tungsten surface without tungsten deposition. Additional tungsten samples were exposed at 1123 K to pure helium plasma with ion incident energy of 76 eV, helium ion fluence of ∼ 3.4 × 10 26 m −2 , and varied W/He ion flux ratio from 0.26 to 3.0 × 10 − 4 . Fuzz thickness increased from 7.5 to 120 µ m with increasing W/He ion ratio. A final sample exposed at 1123 K to a mixed helium-deuterium plasma with ion incident energy of 76 eV, helium ion fluence of 0.18 × 10 26 m −2 , and W/He ion flux ratio of 2.2 × 10 − 4 developed nearly identical fuzz structures to that developed in a pure He plasma. As a function of deposited tungsten fluence, all results were found to trace out a single layer-growth curve given by a power law relation, indicating that fuzz thickness is independent of the W/He ion flux ratio in the range investigated and independent of any deuterium present in the plasma. As a result, for tungsten plasma facing walls in magnetic fusion devices at 1000–2000 K with 10 −4 W/He ion flux ratio, fuzz with thicknesses greater than hundreds of microns may form in as little as 10 4 s (in the absence of ELM-induced erosion or annealing), and may more significantly affect its thermophysical properties than fuzz generated without a tungsten deposition source.

Physics↗
DOE OSTI2023

Deuterium supersaturated surface layer in tungsten: ion energy dependence

Abstract Properties of deuterium (D) supersaturated surface layers (DSSLs) formed in tungsten (W), such as thickness, internal microstructures, and D retention, are experimentally investigated as a function of the incident ion energy, E i . W samples were exposed to D plasmas in the PISCES-A linear plasma device in a range of E i ∼ 45–175 eV, while other plasma exposure parameters were fixed: sample temperature, T s , ∼423 K, ion flux, Γ i , ∼1.2 × 10 21 m −2 s −1 , and fluence, Φ i , ∼3.0 × 10 24 m −2 . High-resolution, cross-sectional, transmission electron microscopy observations confirm that (1) a DSSL forms even at the lowest E i ∼ 45 eV, (2) the DSSL thickness, Δ t DSSL , is found to decrease with decreasing E i from ∼11–12 nm at E i ∼ 175 eV to ∼5–6 nm at ∼45 eV, and to agree with approximately the maximum implantation depth calculated using SDTrimSP, and (3) high-density D nanobubbles with a diameter of ∼1 nm or less exist inside the DSSL, which is deemed to validate a theory-predicted vacancy stabilization process due to trapping of a solute D atom(s). Utilizing a D areal density of ∼4.2 × 10 19 m −2 in the first 14 nm from the surface at E i ∼ 75 eV from nuclear reaction analysis and the measured E i dependence of Δ t DSSL , our previous laser-induced breakdown spectroscopy data is updated: both dynamic and static D retention increase with decreasing E i , and the D/W atomic fraction during plasma exposure reaches ∼0.3 at E i ∼ 45 eV. A possible DSSL formation mechanism is proposed.

Physics↗