•D retention for used W grades varies by more than one order of magnitude.•Hydrogen loading-induced damaging manifests in surface modifications and retention.•Effects of plasma flux on retention and ...surface modifications are discussed.•Higher fluxes produce more severe hydrogen loading-induced damaging.
Five tungsten (W) grades were simultaneously exposed to deuterium (D) plasma with 1020D/(m2s) of 38eV/D up to 1026D/m2 at 500K specimen temperature. The D inventories and their depth profiles within the topmost 12μm were determined by nuclear reaction analysis (D(3He, p)α). Morphological modifications at and below the surface were analysed by confocal laser scanning microscopy and scanning electron microscopy assisted by focused ion beam cross-sectioning. The observed variation of the D inventory by more than one order of magnitude (0.5–15×1020D/m2) is attributed only to the different properties of each W grade. Spherical blisters and stepped flat-topped extrusions are observed depending on the W grade. These modifications are interpreted as an indication for hydrogen loading-induced damaging. The exposure conditions and W grades were chosen to allow a comparison between published data sets.
Fluid flow applications can involve a number of coupled problems. One is the simulation of free-surface flows, which require the solution of a free-boundary problem. Within this problem, the ...governing equations of fluid flow are coupled with a domain deformation approach. This work reviews five of those approaches: interface tracking using a boundary-conforming mesh and, in the interface capturing context, the level-set method, the volume-of-fluid method, particle methods, as well as the phase-field method. The history of each method is presented in combination with the most recent developments in the field. Particularly, the topics of extended finite elements and NURBS-based methods, such as isogeometric analysis, are addressed. For illustration purposes, two applications have been chosen: two-phase flow involving drops or bubbles and sloshing tanks. The challenges of these applications, such as the geometrically correct representation of the free surface or the incorporation of surface tension forces, are discussed.
Tungsten heavy alloy (97 wt% W, 2 wt% Ni, 1 wt% Fe) was investigated as an alternative for tungsten (W) as plasma facing material. It is produced commercially by several companies and compared to ...bulk W it is readily machinable and considerably cheaper. In order to qualify the material for use in the divertor of the mid-size tokamak ASDEX Upgrade (AUG) dedicated laboratory investigations as well as high heat flux tests in the neutral beam facility GLADIS were performed. These investigations revealed that the thermal conductivity at high temperature is close to that of W, the magnetisation is small and saturates already at low magnetic field and the hydrogen retention is similarly low as that of W. In high heat flux tests at power densities up to 20 MWm−2 no failure was observed up to the melting temperature (≈1500∘C) of the binder phase. Even at surface temperatures of up to 2200 °C the mechanical integrity was sustained. Mechanical tests confirm the ductile behaviour of the W heavy alloy at room temperature and finite element analyses using the aforementioned data suggest a lower tendency for cracking. The increase of the long term dose-rate resulting from the activation of Ni under neutron irradiations appears to be moderate. During the 2017 campaign more than one fifth of the AUG divertor tiles consisted of W heavy alloy. Under nominal operation conditions the tiles showed no macroscopic failure and no increased Fe/Ni influx into the plasma was detected. Even though a few tiles showed strong melting at the edges due to accidental misalignment no failure due to cracking was observed.
Abstract
In injection molding, shrinkage and warpage lead to a deformation of the produced parts with respect to the cavity shape. One method to mitigate this effect is to adapt the cavity shape to ...the expected deformation. This deformation can be determined using appropriate simulation models, which then also serve as a basis for determining the optimal cavity shape. Shape optimization usually requires a sequence of forward simulations, which can be computationally expensive. To reduce this computational cost, we use Bayesian optimization which uses Gaussian process regression as a reduced order model. Additionally, Gaussian process regression has the benefit that it allows to account for uncertainty in the model parameters and thus provides a means to investigate their influence on the optimization result. We present a Gaussian process regression trained with samples from a finite‐element solid‐body model. It predicts the deformation of the product after solidification and, together with Bayesian optimization, allows for efficient cavity optimization.
•In order to simulate the influence of deuterium on the evolution of displacement damage 20 MeV tungsten was implanted into already displacement-damaged and deuterium containing tungsten.•Deuterium ...retention increases beyond the value that is known for initially deuterium free, displacement-damaged tungsten by nearly a factor of two.•Rate equation modelling can describe the change in deuterium desorption by assuming only an increase in trap density without changing the de-trapping energies compared to the initial material hence proofing that deuterium is stabilizing the defects created within the collision cascade.
The influence of the presence of deuterium on displacement damage in tungsten is studied by implanting 20 MeV tungsten ions into displacement-damaged tungsten already containing 1.7 at.% deuterium. SDTrimSP calculations reveal that for the tungsten implantation fluence used, on average each D atom is recoiled once and hence mobile deuterium should be present simultaneously while displacing tungsten atoms. Nuclear reaction analysis after the tungsten implantation shows that no deuterium is lost from the sample and the depth profile is unchanged. However, deuterium must have been de-trapped and is effectively re-trapped again because temperature programmed desorption spectroscopy reveals that deuterium is redistributed from the low temperature de-trapping peak to the high temperature de-trapping peak. Rate equation modelling can describe the measured deuterium desorption with the same de-trapping energies as for the initial material but with increased trap densities only. Decorating the samples after the additional tungsten ion implantation again with a low energy deuterium plasma shows increased deuterium retention beyond the saturation value that is known for initially deuterium free, displacement-damaged tungsten by nearly a factor of two. Both observations together indicate that deuterium is stabilizing the defects created within the collision cascade.
•Measurement of magnetisation and thermal conductivity of W–Ni/Fe heavy alloys (D185, HPM1850).•Successful high heat flux testing of W heavy alloys with power densities of up to 20MW/m3.•Exposure of ...W-heavy alloys in the divertor of ASDEX Upgrade in discharges with up 26MW of heating power.
An alternative solution for tungsten as a plasma facing material could be the use of W heavy alloys as they are produced commercially by several companies. They consist of up to 97% W and Ni/Fe (or Ni/Cu) admixtures, they are readily machinable and considerably cheaper than bulk tungsten. Their major drawbacks in view of the application in fusion experiments are the rather low melting temperature and their magnetic properties (in case of a Ni/Fe binder phase). In a first step W heavy alloys from two manufacturers were investigated concerning their thermal and magnetic properties and subjected to screening tests and cyclic loading in the high heat flux test facility GLADIS with up to 20MWm−2 and surface temperatures of up to 2200°C, showing no macroscopic failure. SEM investigations show a segregation of Ni and Fe at the top surface after the thermal overloading, but no signs of micro-cracking. The long-term behaviour of a W–Ni/Fe tile under plasma and electromagnetic load was investigated in ASDEX Upgrade using its divertor manipulator. The tile was exposed in discharges with record values of injected energy and power. Despite the observed surface modifications (Ni/Fe segregation) the W heavy alloys seem to provide a pragmatic and cost-effective alternative to bulk W tiles in the divertor of ASDEX Upgrade.
The modelling of friction is essential for the accuracy of chip formation simulations. Current models are not suitable to represent the influence of lubricants in interaction with different tool ...surfaces in its complexity. The present work aims on the development of a spline-based fluidstructure-contact interaction framework to model the friction of tool, chip and intermediate medium under various conditions. Using this framework, microscopic tribology simulations of the secondary shear zone can be performed to implement a friction coefficient distribution depending on relative speed, temperature and contact normal pressure into a chip formation simulation, which will be validated by experimental data.
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