Be–W alloy formation in static and divertor-plasma simulator experiments

Baldwin, M.J.; Doerner, R.; Nishijima, D.; Buchenauer, D.; Clift, W. Miles; Causey, R.A.; Schmid, K.

doi:10.1016/j.jnucmat.2007.01.151

Cited by 51 publications

(55 citation statements)

References 7 publications

(9 reference statements)

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“…The best values were found to be: center = 0.9, full width = 0.05, height = 5 × 10 −20 (m 2 s −1 ). To estimate E D the diffusion coefficient estimates from [19] Fig. 2 where fitted to an arrhenius function yielding an activation energy of 4.5eV.…”

Section: = Binding Energy Of Element I On An Element J Surfacementioning

confidence: 99%

Beryllium flux distribution and layer deposition in the ITER divertor

Schmid

2008

Nucl. Fusion

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Abstract.The deposition of Be eroded from the main chamber wall on the W surfaces in the ITER divertor could result in the formation of Be rich Be/W mixed layers with a low melting temperature compared to pure W. To predict whether or not these layers form the Be flux distribution in the ITER divertor is required. This paper presents the results of a combination of plasma transport-with erosion/deposition simulations that allow to calculate both the Be flux distribution and the Be layer deposition in the ITER divertor. This model includes the Be source due to Be erosion in the main chamber and the deposition, re-erosion and re-deposition of Be in the ITER divertor. The calculations show that the fraction of Be in the incident particle flux in the divertor range from ≈ 10 −3 to ≈ 5% with a pronounced inner outer divertor asymmetry. The flux fractions in the inner divertor are on average ten times higher than in the outer divertor. Thick Be layers only from at the inner strike point and the dome baffles. The highest Be layer growth rate is found to be 1.0 nm/s. Despite the Be deposition the formation of Be rich Be/W mixed layers is not to be expected in ITER. The expected surface temperature at these locations during steady state operation is too low as to result in Be diffusion into W and thus Be/W mixed layers can not form.

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Section: = Binding Energy Of Element I On An Element J Surfacementioning

confidence: 99%

Beryllium flux distribution and layer deposition in the ITER divertor

Schmid

2008

Nucl. Fusion

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“…These experiments explore the W−Be material mixing and its properties under fusion reactor like conditions, such as the formation of different surface structures (Be deposition, W-Be alloying or W fuzz nano-morphologies) [1,2,3] and the effect of Be on the long-term D retention [4,5] and erosion yields [6]. Besides the experimental work, particle balance models for W−Be material mixing [3], dynamic Monte Carlo simulations of Be deposition-erosion processes [6] and empirical equations accounting for the influence of the substrate temperature, recoil energy and the D to Be ratio [5] can be found in the literature. However, a detailed computational study of the above mentioned processes and a reliable database for the erosion, deposition and reflection yields is lacking; a single nano-scale study exists, focused on the Be erosion from Be 2 W surfaces [7].…”

Section: Introductionmentioning

confidence: 99%

Modelling of W–Be mixed material sputtering under D irradiation

2014

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Abstract. We present an atomistic study on the D irradiation on W-Be mixtures, including a comparison between Molecular Dynamics and Binary Collision Approximation methods. We compared the D reflection and Be erosion yields after the non-cumulative D impacts, concluding that both methods agree qualitatively, but low energy irradiation related chemical effects can be recognized in MD. We also followed the evolution of W-Be mixtures under cumulative D irradiation. At low energies, the surface deuterates, quickly saturating the D reflection and suppressing the Be erosion.

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“…An especially obvious example for such an effect is the formation of a low melting Be-W alloy as observed in PISCES-B [41]. The formation of the alloy depends delicately on the amount of Be in the plasma, the plasma conditions leading to either deposition of Be or a steady erosion of W and the surface temperature which strongly influences the Be diffusion into W and its sublimation [42,43,44]. The complexity of this process requires detailed modelling (or experiments) in order to judge the potential impact of it.…”

Section: Blisters Bubbles and Mixed Materials Effectsmentioning

confidence: 99%

Benefits and Challenges of the Use of High-Z Plasma Facing Materials in Fusion Devices

Neu

2010

AIP Conference Proceedings

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Abstract.The use of high-Z plasma facing components requires intensive research in all areas, i.e. in plasma wall-interaction, in the physics of the confined plasma, diagnostic, and in material development. Only a few present day divertor tokamaks -mainly Alcator C-Mod and ASDEX Upgrade -gained experience with the refractory metals molybdenum and tungsten, respectively. ASDEX Upgrade was stepwise converted from graphite to tungsten PFCs and in parallel a reduction of the deuterium retention by almost a factor of ten has been observed due to the strong suppression of D co-deposition with carbon. The deuterium retained in W is in line with laboratory results. In order to diagnose W sources and the W content in the main plasma adequate spectroscopic methods had to be developed. As expected from the sputtering threshold of Mo and W, negligible erosion by the thermal divertor background plasma is found in ASDEX Upgrade and Alcator C-Mod under low temperature divertor conditions. However, erosion by fast particles and intrinsic impurities, which additionally might be accelerated in rectified electrical fields observed during ion cyclotron frequency heating, plays an important role. The Mo and W concentrations in the plasma centre are strongly affected by plasma transport and variations up to a factor of 50 are observed for similar influxes. However, it could be demonstrated that sawteeth and turbulent transport driven by central heating can suppress central accumulation. The inward transport of high-Z ions at the edge can be efficiently reduced by 'flushing' the pedestal region caused by frequent edge instabilities. Since with metal walls the edge radiation by low-Z impurities is reduced, it has to be substituted in a pure high-Z device by artificially injected low-Z impurities in order to keep the power load at an acceptable level. Experiments at ASDEX Upgrade suggest that a regime with benign erosion and favourable confinement can be achieved. Extrapolations to ITER and DEMO are difficult since the physics of plasma transport is not yet completely understood, the particle and energy fluxes are orders of magnitude higher and the technical boundary conditions in DEMO strongly differ from those of present day devices.

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Be–W alloy formation in static and divertor-plasma simulator experiments

Cited by 51 publications

References 7 publications

Beryllium flux distribution and layer deposition in the ITER divertor

Beryllium flux distribution and layer deposition in the ITER divertor

Modelling of W–Be mixed material sputtering under D irradiation

Benefits and Challenges of the Use of High-Z Plasma Facing Materials in Fusion Devices

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