Experimental and theoretical investigation of droplet emission from tungsten melt layer

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

doi:10.1016/j.fusengdes.2008.12.123

Cited by 54 publications

(44 citation statements)

References 4 publications

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“…The j × B force originates from thermoelectric emission following the RichardsonDushman equation [16,7]. Meltlayer motion as observed in the Quasi Stationary Plasma Accelerator (QSPA) facilities [3,4,5,6] is driven by the high plasma pressure (∼ 10 5 Pa). Few studies have in addition considered Lorentz-forces (F j×B ) due to thermoelectric emission and those have been done at medium B-fields (1.4T ) [17].…”

Section: Results and Measurementsmentioning

confidence: 99%

“…Few studies have in addition considered Lorentz-forces (F j×B ) due to thermoelectric emission and those have been done at medium B-fields (1.4T ) [17]. The driving force which has been identified as cause for bridging the castellation is the inertia of the melt at the gap edge competing with the surface tension, melt layer splashing is assumed to be caused due to high velocity shears leading to Kelvin-Helmholtz instabilities [5,4]. During tokamak experiments the situation is quite different.…”

Section: Results and Measurementsmentioning

confidence: 99%

“…For ITER steady EXD/6-1 state heat loads for a tungsten divertor plate are expected to range around 5 − 10M W/m 2 under normal operation conditions in the non-activated phase, loss of positioning control or additional transients as well as possible misalignment of target mono-blocks can thus lead to melting [1,2]. Studies on melt-layer motion have been performed in electron and ion beam facilities [3,4,5,6] showing significant melt motion, splashing and changes in the material structure and their power handling capabilities. Few results exist regarding behavior under tokamak conditions, including magnetic fields, large currents through the PFC surfaces and various power impact scenarios (Steady state, ELMs, VDEs or disruptions) as well as high temperature erosion.…”

Section: Introductionmentioning

confidence: 99%

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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: Results and Measurementsmentioning

confidence: 99%

Section: Results and Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2011

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“…In [15], bubble boiling is seen as the most likely explanation for macroscopic melt-layer ejection in the form of spraying (figure 8) apart from the so-called Kelvin-Helmholtz-instability when considering fast moving melt layers not present under TEXTOR conditions [16,17]. Bubble formation requires a seed to form, such as grain boundaries, impurity clusters or microscopic irregularities.…”

Section: Materials Structure Evolutionmentioning

confidence: 99%

Melt-layer ejection and material changes of three different tungsten materials under high heat-flux conditions in the tokamak edge plasma of TEXTOR

et al. 2011

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Abstract.The behaviour of tungsten (W) plasma-facing components (PFCs) has been investigated in the plasma edge of the TEXTOR tokamak to study melt-layer ejection, macroscopic tungsten erosion from the melt layer as well as the changes of material properties such as grain-size and abundance of voids or bubbles. The parallel heat flux at the radial position of the exposed tungsten tile in the plasma ranges around q ‖ ∼ 45 MW m −2 causing samples to be exposed at an impact angle of 35º to 20-30 MW m −2 . Locally the temperature reached up to 6000 K, high levels of evaporation and boiling are causing significant erosion in the form of continuous fine spray or droplet ejection. The amount offine-spray tungsten emission depends strongly on the material properties: in the case of the tungsten-tantalum alloy the effect of spraying and droplet emission is significantly higher at even low temperatures when compared with regular tungsten or even ultra-high purity tungsten which shows almost no spraying at all. Differences in the material composition, grain structure and size may be related to the different evolution of macroscopic erosion. In addition the re-solidified material is studied and strong differences in terms of re-crystallized grain size and evolution of the grain structure and grain orientation are observed. The build up of large voids has been observed.

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“…In [51] one explains why the first nano-structural layer arises involving the mechanism of Kelvin-Helmholtz instability [30] in the nano-dimensional range of wavelengths in conditions of tangentiall-flowing plasma and a layer of molten metal. If two media are moving relative to each other, waves appear (like ripples on water's surface when it is windy).…”

Section: Modeling Of Subsurface Nanostructure Formationmentioning

confidence: 99%

Mathematical Modeling of the Concentrated Energy Flow Effect on Metallic Materials

Konovalov

Chen

Sarychev

et al. 2016

Metals

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Numerous processes take place in materials under the action of concentrated energy flows. The most important ones include heating together with the temperature misdistribution throughout the depth, probable vaporization on the surface layer, melting to a definite depth, and hydrodynamic flotation; generation of thermo-elastic waves; dissolution of heterogeneous matrix particles; and formation of nanolayers. The heat-based model is presented in an enthalpy statement involving changes in the boundary conditions, which makes it possible to consider melting and vaporization on the material surface. As a result, a linear dependence of penetration depth vs. energy density has been derived. The model of thermo-elastic wave generation is based on the system of equations on the uncoupled one-dimensional problem of dynamic thermo-elasticity for a layer with the finite thickness. This problem was solved analytically by the symbolic method. It has been revealed for the first time that the generated stress pulse comprises tension and compression zones, which are caused by increases and decreases in temperature on the boundary. The dissolution of alloying elements is modeled on the example of a titanium-carbon system in the process of electron beam action. The mathematical model is proposed to describe it, and a procedure is suggested to solve the problem of carbon distribution in titanium carbide and liquid titanium-carbide solution in terms of the state diagram and temperature changes caused by phase transitions. Carbon concentration vs. spatial values were calculated for various points of time at diverse initial temperatures of the cell. The dependence of carbon particle dissolution on initial temperature and radius of the particle were derived. A hydrodynamic model based on the evolution of Kelvin-Helmholtz instability in shear viscous flows has been proposed to specify the formation of nanostructures in materials subjected to the action of concentrated energy flows. It has been pointed out for the first time that, for certain parameters of the problem, that there are two micro-and nanoscale peaks in the relation of the decrement to the wavelength of the interface disturbance.

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Experimental and theoretical investigation of droplet emission from tungsten melt layer

Cited by 54 publications

References 4 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

Melt-layer ejection and material changes of three different tungsten materials under high heat-flux conditions in the tokamak edge plasma of TEXTOR

Mathematical Modeling of the Concentrated Energy Flow Effect on Metallic Materials

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