Experiments and modeling of droplet emission from tungsten under transient heat loads

Базылев, Б.; Landman, I.; Loarte, A.; Климов, Н. С.; Podkovyrov, V. L.; Safronov, V.M.

doi:10.1088/0031-8949/2009/t138/014061

Cited by 23 publications

(22 citation statements)

References 6 publications

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“…Figure 11: Ligament structures after exposure Part of the splashing and spraying events is the evolution of ligament like structures which seem to have a quite regular pattern probably following the plasma flow and or the melt motion on the surface and beyond. As predicted in [29,30] instabilities are evolving due to the plasma flow and the melt-layer motion and the velocity shear between them. Critical levels of velocity shear still maybe reached or recoil may trigger splashing as described in [22].…”

Section: Tungsten Erosionmentioning

confidence: 80%

Analysis of tungsten melt-layer motion and splashing under tokamak conditions at TEXTOR

et al. 2011

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Behavior and characteristics of tungsten under impinging high heat-fluxes are investigated in view of the material choices for future devices such as ITER and DEMO. Experiments have been performed in the edge of the TEXTOR tokamak to study melt-layer motion, macroscopic melt layer erosion as well as the changes of the material properties. The parallel heat-flux ranges around q ∼ 45M W/m 2 allowing samples at an impact angle of 35 • to be exposed to 20 − 30M W/m 2 . Melt-layer motion perpendicular to the magnetic field is observed following a Lorentzforce originating from thermoelectric emission of the hot sample. Up to 3 g of tungsten are redistributed forming mountain like structures at the edge of the sample. The typical melt layer thickness is 1 − 1.5mm. Those hills are particularly susceptible to even higher heat-fluxes of up to the full q . Locally the temperature can reach up to 6000K, high levels of evaporation are causing significant erosion in form of continuous fine-spray (∼ 1 · 10 24 atoms m −2 s −1 ). Vaporshielding is occurring and hindering the further heating of the samples. In addition the formation of ligaments and splashes occurs several times during the melt phase ejecting droplets in the order of several 10µm up to 100µm probably caused by a Kelvin-Helmholtz instability evolving in the melt. In terms of material degradation several aspects are considered: formation of leading edges by redistributed melt, bubble formation and re-crystallization. Bubbles are occurring in sizes between µm and 200 µm while recrystallization increases the grain size up to 1.5 mm. The power handling capabilities are thus severely degraded. Melting of Tungsten in future devices is highly unfavorable and needs to be avoided especially in light of uncontrolled transients and possible unshaped PFCs

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Section: Tungsten Erosionmentioning

confidence: 80%

Analysis of tungsten melt-layer motion and splashing under tokamak conditions at TEXTOR

et al. 2011

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“…In all cases, droplets are injected over a 3 ms duration following the TQ onset, and a parameter scan is performed on their initial radius and velocity. Although numerical modelling of metallic melt layer dynamics under ITER-relevant conditions is available [8,[24][25][26], to our knowledge, no experimental validations currently exist regarding the size, speed and angle distributions of the Be droplets which may be ejected from the melt layers. Experimental observations of Be PFC exposure to VDEs in JET [27,28] suggest a droplet size of the order of a few μm, but the extrapolation of these results to ITER is uncertain due to the upscaling of plasma energy.…”

Section: Droplet Injection Scheme and Post-treatmentmentioning

confidence: 99%

“…Experimental observations of Be PFC exposure to VDEs in JET [27,28] suggest a droplet size of the order of a few μm, but the extrapolation of these results to ITER is uncertain due to the upscaling of plasma energy. More detailed experiments on W droplets in plasma guns report typical sizes of several tens of μm [29][30][31][32][33][34] and most probable ejection speeds of a few m s −1 , which are expected to increase by a factor 3 in the case of Be due to the main scaling with mass density [8,24,30,31,33,35]. Given these uncertainties, the choice is made here to scan a wide enough range of droplet characteristics so as to capture the influence of these parameters and draw generic conclusions on droplet cooling.…”

Section: Droplet Injection Scheme and Post-treatmentmentioning

confidence: 99%

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Survival and in-vessel redistribution of beryllium droplets after ITER disruptions

et al. 2018

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The motion and temperature evolution of beryllium droplets produced by first wall surface melting after ITER major disruptions and vertical displacement events mitigated during the current quench are simulated by the MIGRAINe dust dynamics code. These simulations employ an updated physical model which addresses droplet-plasma interaction in ITER-relevant regimes characterized by magnetized electron collection and thin-sheath ion collection, as well as electron emission processes induced by electron and high-Z ion impacts. The disruption scenarios have been implemented from DINA simulations of the time-evolving plasma parameters, while the droplet injection points are set to the first-wall locations expected to receive the highest thermal quench heat flux according to field line tracing studies. The droplet size, speed and ejection angle are varied within the range of currently available experimental and theoretical constraints, and the final quantities of interest are obtained by weighting single-trajectory output with different size and speed distributions. Detailed estimates of droplet solidification into dust grains and their subsequent deposition in the vessel are obtained. For representative distributions of the droplet injection parameters, the results indicate that at most a few percents of the beryllium mass initially injected is converted into solid dust, while the remaining mass either vaporizes or forms liquid splashes on the wall. Simulated in-vessel spatial distributions are also provided for the surviving dust, with the aim of providing guidance for planned dust diagnostic, retrieval and clean-up systems on ITER.

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“…This phenomenon occurs when there is a difference in velocity across the interface between two fluids. Furthermore, it has been reported that the Kelvin-Helmholtz instability can also lead to the evolution of shock waves along the surface of the fluid causing a breakup of the melt surface into droplets [35].…”

Section: Resultsmentioning

confidence: 99%

Development of Wire + Arc additive manufacture for the production of large-scale unalloyed tungsten components

Marinelli

Martina

Ganguly

et al. 2019

International Journal of Refractory Metals and Hard Materials

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The manufacturing of refractory-metals components presents some limitations induced by the materials' characteristic low-temperature brittleness and high susceptibility to oxidation. Powder metallurgy is typically the manufacturing process of choice. Recently, Wire + Arc Additive Manufacturing has proven capable to produce fully-dense large-scale metal parts at relatively low cost, by using highquality wire as feedstock. In this study, this technique has been used for the production of large-scale tungsten linear structures. The orientation of the wire feeding has been studied and optimised to obtain defect-free tungsten deposits. In particular, front wire feeding eliminated the occurrence of pores and micro-cracks, when compared to side wire feeding. The microstructure, the occurrence of defects and their relationship with the deposition process have also been discussed. Despite the repetitive thermal cycles and the inherent brittleness of the material, the asdeposited structures were free from internal cracks and the layer dimensions were stable during the entire deposition process. This enabled the production of a relatively large-scale component, with the dimension of 210 x 75 x 12 mm. This study has demonstrated that Wire + Arc Additive Manufacture can be used to produce large-scale parts in unalloyed tungsten by complete fusion, presenting a potential alternative to the powder metallurgy manufacturing route.

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Experiments and modeling of droplet emission from tungsten under transient heat loads

Cited by 23 publications

References 6 publications

Analysis of tungsten melt-layer motion and splashing under tokamak conditions at TEXTOR

Analysis of tungsten melt-layer motion and splashing under tokamak conditions at TEXTOR

Survival and in-vessel redistribution of beryllium droplets after ITER disruptions

Development of Wire + Arc additive manufacture for the production of large-scale unalloyed tungsten components

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