Exposures of tungsten nanostructures to divertor plasmas in DIII-D

Rudakov, D.L.; Wong, C.P.C.; Doerner, R.; Wright, G.M.; Abrams, T.; Baldwin, M.J.; Boedo, J.A.; Briesemeister, A.; Chrobak, C.; Guo, H.Y.; Hollmann, E. M.; McLean, A.G.; Fenstermacher, M.E.; Lasnier, C.J.; Leonard, A. W.; Moyer, R. A.; Pace, D. C.; Thomas, D. M.; Watkins, J. G.

doi:10.1088/0031-8949/t167/1/014055

Cited by 35 publications

(17 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The low-pitch tracks must have appeared during controlled phases of diverted discharges when the field line pitch angle is small. Tracks with the angle ∼10 • must be due to disruptions, similar to experiment [4]. The two preferential inclinations are due to forward and reversed B t .…”

Section: Post Mortem Tile Analysismentioning

confidence: 52%

“…Still, there is no arc avoidance strategy proposed compatible with high-performance tokamak operation. Arcing has been studied in many machines, either in dedicated experiments with small-scale test samples exposed in a limited number of discharges with controlled parameters [4][5][6], or by performing shutdown in-vessel surveys of permanently installed components assessing integrated effect of arcing after the whole campaign [2,7]. In June-July 2016, a short-term Metal Rings Campaign (MRC) was conducted at DIII-D to study W sourcing in the divertor, W migration, transport, and core contamination, and to explore high-Z wall compatibility with high performance plasmas [8,9].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Tungsten erosion by unipolar arcing in DIII-D

Bykov¹,

Chrobak²,

Abrams³

et al. 2017

Phys. Scr.

Self Cite

View full text Add to dashboard Cite

Unipolar arcing was an important mechanism of metal surface erosion during the recently conducted Metal Rings Campaign in DIII-D when two toroidally continuous tile rings with 5 cm wide W-coated TZM inserts were installed in graphite tiles in the lower divertor, one on the floor and one on the shelf. Most of the arc damage occurred on the shelf ring. The total amount of W removed by arcing from the affected ∼4% of the shelf ring area was estimated ∼0.8×10 21 at., about half of the total amount of W eroded and redeposited outside the inserts (1.8±0.9)×10 21 at. The rings were exposed for a total of ∼480 discharges, an equivalent of plasma time on W surfaces (with Ip >0.5 MA) ∼10 3 s. Arcing was monitored in situ with WI (400.9 nm) filtered camera and photomultipliers and showed that: (i) arcing only occurred during ELMs and disruptions, (ii) arcing rate was much lower on the floor than on the shelf ring, and (iii) arcing had a low cut off power flux density about 2 MW/m 2. About half of arc tracks had large 10 • pitch angle and probably were produced during disruptions. Such tracks were only found on the shelf. Moderate toroidal variation of the arc track density and W erosion with nearly n=1 pattern has been measured.

show abstract

Section: Post Mortem Tile Analysismentioning

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Tungsten erosion by unipolar arcing in DIII-D

Bykov¹,

Chrobak²,

Abrams³

et al. 2017

Phys. Scr.

Self Cite

View full text Add to dashboard Cite

show abstract

“…This “fuzz” is essentially a conglomerated mass of interconnecting surface tendrils resulting from accumulation, growth, and rupture of subsurface He bubbles. While the formation of W fuzz is generally concerning for the operation of nuclear fusion reactors, − exposing these high-surface-area fuzzy structures allows for rapid oxidation and efficient production of nanostructured W oxide surfaces. Because of a developing interest in refractory metal oxide nanostructures, these fusion-relevant fuzzy W surfaces have been applied toward alternative applications such as solar light absorption, solar water splitting, and photocatalysts with promising results.…”

Section: Introductionmentioning

confidence: 99%

Nb₂O₅ Nanostructure Evolution on Nb Surfaces via Low-Energy He⁺ Ion Irradiation

Novakowski

Tripathi

Hassanein

2016

ACS Appl. Mater. Interfaces

View full text Add to dashboard Cite

We propose low-energy, broad-beam He ion irradiation as a novel processing technique for the generation of NbO surface nanostructures due to its relative simplicity and scalability in a commercial setting. Since there have been relatively few studies involving the interaction of high-fluence, low-energy He ion irradiation and Nb (or its oxidized states), this systematic study explores both effects of fluence and sample temperature during irradiation on resulting surface morphology. Detailed normal and cross-sectional scanning electron microscopy (SEM) studies reveal subsurface He bubble formation and elucidate potential driving mechanisms for nanostructure evolution. A combination of specular optical reflectivity and X-ray photoelectron spectroscopy (XPS) is also used to gain additional information on roughness and stoichiometry of irradiated surfaces. Our investigations show significant surface modification for all tested irradiation conditions; the resulting surface structure size and geometry have a strong dependence on both sample temperature during irradiation and total ion fluence. Optical reflectivity measurements on irradiated surfaces demonstrate increased surface roughening with increasing ion fluence, and XPS shows higher oxidation levels for samples irradiated at lower temperatures, suggesting larger surface roughness and porosity. Overall, it was found that low-energy He ion irradiation is an efficient processing technique for nanostructure formation, and surface structures are highly tunable by adjusting ion fluence and NbO sample temperature during irradiation. These findings may have excellent potential applications for solar energy conversion through improved efficiency due to effective light absorption.

show abstract

“…The use of an ITER full tungsten divertor [1] is being tested at a number of controlled fusion tokamaks, including JET [2] and ASDEX-UPGRADE [3]. The DIII-D tokamak is also performing experiments using tungsten [4]. Electron-ionization and electron-recombination rate coefficients are needed in impurity transport codes to predict the amount of tungsten present in the core of the controlled fusion tokamaks [5].…”

Section: Introductionmentioning

confidence: 99%

Electron-impact ionization ofW27+

Pindzola

Loch

2016

Phys. Rev. A

View full text Add to dashboard Cite

Electron-impact ionization cross sections for W 27+ are calculated using a semi-relativistic configuration-average distorted-wave (CADW) method. Calculations for direct ionization, excitation-autoionization, and branching ratios are compared with recent calculations by Jonauskas et al. (PRA 91, 012715 (2015)) who used fully-relativistic subconfiguration-average distortedwave (SCADW) and level to level distorted-wave (LLDW) methods. Reasonable agreement is found between the new CADW and the recent LLDW calculations for direct ionization of the 4l(l = 0 − 1, 3) subshells, but not the 4d subshell, and between the new CADW and recent SCADW/LLDW calculations for excitation-autoionization of the 4l(l = 0 − 2) subshells. Reasonable agreement is also found between the new CADW and the recent SCADW calculations including branching ratios, but both differ from the recent LLDW calculations. Additional CADW calculations are made for excitation-autoionization including branching ratios involving the important 3l(l = 1 − 2) subshells, not examined by Jonauskas et al. (PRA 91, 012715 (2015)).

show abstract

Exposures of tungsten nanostructures to divertor plasmas in DIII-D

Cited by 35 publications

References 14 publications

Tungsten erosion by unipolar arcing in DIII-D

Tungsten erosion by unipolar arcing in DIII-D

Nb₂O₅ Nanostructure Evolution on Nb Surfaces via Low-Energy He⁺ Ion Irradiation

Electron-impact ionization ofW27+

Contact Info

Product

Resources

About

Exposures of tungsten nanostructures to divertor plasmas in DIII-D

Cited by 35 publications

References 14 publications

Tungsten erosion by unipolar arcing in DIII-D

Tungsten erosion by unipolar arcing in DIII-D

Nb2O5 Nanostructure Evolution on Nb Surfaces via Low-Energy He+ Ion Irradiation

Electron-impact ionization ofW27+

Contact Info

Product

Resources

About

Nb₂O₅ Nanostructure Evolution on Nb Surfaces via Low-Energy He⁺ Ion Irradiation