key parameters for plasma-material interaction...key parameters: diffusion, solubility, permeation...
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![Page 1: Key parameters for Plasma-Material Interaction...Key parameters: Diffusion, Solubility, Permeation Example: Situation for H in tungsten Recommended value: 0.39 eV (Frauenfelder) [Causey,](https://reader034.vdocuments.site/reader034/viewer/2022051901/5ff0f42a00c9926612452e7b/html5/thumbnails/1.jpg)
IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
Key parameters forPlasma-Material Interaction
U. von Toussaint, A. Mutzke, D. Coster,
Th. Schwarz-Selinger, R. Preuss
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
Introduction
Classical Focus of Particle-wall interaction in fusion: ● Sputter yield Y(E,angle,species) and reflection: well studied for pure samples &
atomic projectiles● Collision cascade in binary collision approximation: O(10 12⁻ sec)
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
Introduction
Particle-wall interaction: ● Wall is part of complex PMI interplay● Time scales O(10-12 sec) – O(10+3 sec)● Similar for spatial scales O(nm) – O(m)
Large number of coupled processes (→ this meeting). ● Here: hydrogen transport in material
by D. Whyte, FPAM (2010)
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
I. Hydrogen transport in materials
Tritium retention and transport in material crucial ● Key parameters: Diffusion, Solubility, Permeation● Example: Situation for H in tungsten
l
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
I. Hydrogen transport in materials
Tritium retention and transport in material crucial ● Key parameters: Diffusion, Solubility, Permeation● Example: Situation for H in tungsten● Recommended value: 0.39 eV (Frauenfelder) [Causey, PhysScr T94,9 (2001)]
Data from 1969, recent DFT-calculations: 0.25 eV
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
I. Hydrogen transport in materials
Tritium retention and transport in material crucial ● Key parameters: Diffusion, Solubility, Permeation● Example: Situation for H in tungsten● Discrepancy by factor of 60 between data from 1969 and 2001
![Page 7: Key parameters for Plasma-Material Interaction...Key parameters: Diffusion, Solubility, Permeation Example: Situation for H in tungsten Recommended value: 0.39 eV (Frauenfelder) [Causey,](https://reader034.vdocuments.site/reader034/viewer/2022051901/5ff0f42a00c9926612452e7b/html5/thumbnails/7.jpg)
IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
I. Hydrogen transport in materials
Tritium retention and transport in material crucial ● Key parameters: Diffusion, Solubility, Permeation● Limited database for fusion relevant materials (W, Be)● No reliable uncertainty quantification even for fundamental properties● Why?
Many reasons, eg. research focus in 70s different (hydrogen storage)
● Dedicated experiments with extended temperature range needed● In principle straightforward, but
● High sensitivity needed
● Measurements influenced by defects (trapping)
● ...
● In addition: ● Responsibility?
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
II. Hydrogen retention in materials
Tritium retention and transport ● Key parameters: trapping energies, trap density, trap distribution● Experiment: Thermal desorption spectroscopy
● Results are inconclusive: typically broad peaks – in literature 15 (!) different val.
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
II. Hydrogen retention in materials
Tritium retention and transport ● Effect of depth profile commonly neglected :-(
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
II. Hydrogen retention in materials
Tritium retention and transport ● Depth profile itself based on ill-conditioned inversion problem
but old cross-sections were systematically shifted :-(
(NIM B 371 (2016) 41)
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
II. Hydrogen retention in materials
Tritium retention and transport ● Trap energies are key component for retention and permeation modelling● Present status not satisfying● TDS evaluation challenging (ill-conditioned deconvolution problem)● Atomistic parameters (ie. frequency-factor) typically set to fixed value (??)
Round-robin experiments indicated
● Stronger modelling support needed (T>0 K)
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
III. Molecular Dynamic Potentials
Molecular dynamic simulations ● Simulation results depend on potential● Standard approach: Fitting of parametric function to ab-initio/DFT/exp. data● Parameter space high-dimensional: quality check – challenging ● MD-potentials at core of multiscale approaches
Automated closed-loop potential development necessary
Approach based on Bayesian Gaussian processesappears feasible
Adapted from B. Wirth, JNM 329 (2010), p. 103
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
Conclusion
Plasma.Material-Interaction:
- many basic data even for key materials are lacking or uncertain
- steel (i.e. EUROFER) as 'new' PWI material: next level of complexity of PMI – huge parameter space
- benchmarking and validation will be crucial (expect the unexpected)
Strong need for joint experimental & modelling campaigns
Who is/ wants to be/ needs to be in charge?
Next level of complexity:
strong surface morphology development
5 µm
GLADIS test: H. Greuner, H. Maier, M. Balden
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
IV. Status and Outlook
Thank youfor yourattention
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
I. The atomistic level
Basis of all subsequent PMI effects: atomic collisions
- Collision events/cascades by impinging particles:
● Displacements
● Defect formation
● Erosion due to physical sputtering
- Modelling tools:
● Binary collision (BC) models (e.g. TRIM)
● Molecular dynamic simulations
MD alleviates restrictions of BC codes:
● Low energy (< ~50 eV)
● MoleculesK. Tichmann, U. von Toussaint, W. Jacob, JNM 420 (2012), p. 291
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IAEA, TM on UQ for Atomic data for Fusion, IPP, 19.12.2016
I. The atomistic level
Damage by energetic particles
- Number of displaced atoms: ● NRT-model: N
D=0.8 T
d(E) / (2E
Th) ~ E
– Eth=? (for tungsten: 40 eV, 90 eV,...)
– Linear dependence correct?
- MD simulations: Eth of tungsten: strong anisotropy
Eth (eV)
R.E. Stoller (2012)
U. von Toussaint (2012)
100
001
010