Stress-driven surface swell and exfoliation of copper as the plasma-facing materials in NBI ICP source

Neutral beam injection (NBI) heating is a significant auxiliary heating method used in Tokamak fusion devices. The material of faraday shield (FS) and accelerator grids in the NBI inductively coupled plasma (ICP) source can be damaged during operation by the high-density hydrogen plasma irradiation, and thus affecting the stability of the NBI system. In this paper, a series of hydrogen plasma exposure experiments are performed on oxygen-free copper (OFC) specimens at 400-850 K with ion energy of 20-200 eV and irradiation fluence up to 1.0×1025 /m2. Meanwhile, the rate equation model is adopted for numerical simulation of the bubble growth and hydrogen retention. The influence of OFC surface temperature, hydrogen ion energy and fluence on OFC damage are experimentally and numerically investigated. Surface observations show that swell and exfoliation are formed on the OFC samples at 400 K and 600 K by scanning electron microscopy (SEM). The hydrogen ion energy varying from 20 to 200 eV at 400 K is observed to have little effect on OFC surface microstructure. The simulative results show that there exist different critical temperatures when the initial bubble radius changes. The bubble surface density rises and the bubble size decreases with increasing temperature (below the critical temperature). In addition, adjacent bubbles get closer to each other with the growth of hydrogen bubbles, and the strong tensile stress is produced inside the surrounding material of hydrogen bubbles. Some cracks caused by hydrogen bubbles appear on the surface of the OFC to relax the pressure-induced stress, ultimately leading to OFC FS/grids material damage. This investigation helps to understand hydrogen retention and failure mechanisms of OFC materials under extreme operation conditions in the NBI devices.

Computational Study of the Dynamics of the Taylor Bubble

We perform high-resolution numerical simulations of three-dimensional dynamics of an elongated bubble in a microchannel at moderate Reynolds numbers up to 1800. For this purpose, we use the coupled Brinkman penalization and volume of fluid methods implemented in the open-source framework Basilisk. The new results are validated with available experimental data and compared with previous numerical and theoretical predictions. We extend existing results to regimes with significant inertia, which are characterized by intense deformations of the bubble, including cases with azimuthal symmetry breaking. Various dynamical features are analyzed in terms of their spatiotemporal characteristics, such as frequencies and wavelengths of the bubble surface undulations and vortical structures in the flow.

Influence of Temperature on Rising Bubble Dynamics in Water and n-pentanol Solutions

Data in the literature on the influence of water temperature on the terminal velocity of a single rising bubble are highly contradictory. Different variations in bubble velocity with temperature are reported even for potentially pure systems. This paper presents a systematic study on the influence of temperature between 5 °C and 45 °C on the motion of a single bubble of practically constant size (equivalent radius 0.74 ± 0.01 mm) rising in a clean water and n-pentanol solution of different concentrations. The bubble velocity was measured by a camera, an ultrasonic sensor reproduced in numerical simulations. Results obtained by image analysis (camera) were compared to the data measured by an ultrasonic sensor to reveal the similar scientific potential of the latter. It is shown that temperature has a significant effect on the velocity of the rising bubble. In pure liquid, this effect is caused only by modifying the physicochemical properties of the water phase, not by changing the hydrodynamic boundary conditions at the bubble surface. In the case of the solutions with surface-active substances, the temperature-change kinetics of the dynamic adsorption layer formation facilitate the immobilization of the liquid/gas interface.

Foaming and rheological properties of aqueous solutions: an interfacial study

Although aqueous foam is composed of simple fluids, air and water, it shows a complex rheological behavior. It exhibits solid-like behavior at low shear and fluid-like behavior at high shear rate. Therefore, understanding such behavior is important for many industrial applications in foods, pharmaceuticals, and cosmetics. Additionally, air–water interface of bubble surface plays an important role in the stabilizing mechanism of foams. Therefore, the rheological properties associated with the aqueous foam highly depend on its interfacial properties. In this review, a systematic study of aqueous foam are presented primarily from rheology point of view. Firstly, foaming agents, surfactants and particles are described; then foam structure was explained, followed by change in structure under applied shear. Finally, foam rheology was linked to interfacial rheology for the interface containing particles whose surface properties were altered by surfactants.

Dissociated prismatic loop punching by bubble growth in FCC metals

Materials performance can be significantly degraded due to bubble generation. In this work, the bubble growth process is elaborated in Cu by atomistic modeling to bridge the gap of experimental observations. Upon continuous He implantation, bubble growth is accommodated first by nucleation of dislocation network from bubble surface, then formation of dissociated prismatic dislocation loop (DPDL), and final DPDL emission in $$\langle 110\rangle$$ ⟨ 110 ⟩ directions. As the DPDL is found capable of collecting He atoms, this process is likely to assist the formation of self-organized bubble superlattice, which has been reported from experiments. Moreover, the pressurized bubble in solid state manifests the shape of an imperfect octahedron, built by Cu $$\{111\}$$ { 111 } surfaces, consistent with experiments. These atomistic details integrating experimental work fill the gap of mechanistic understanding of athermal bubble growth in Cu. Importantly, by associating with nanoindentation testings, DPDL punching by bubble growth arguably applies to various FCC (face-centered cubic) metals such as Au, Ag, Ni, and Al.

STUDY OF SEDIMENTS OF COLLECTING AGENTS IN ELEMENTARY FLOTATION ACT

The operating mechanism of physically sorbed derivatives of collector obtained at a nonstoichiometric ratio between collecting agents with heavy metal salts is proposed. It is found that by changing the ratio of the components, it is possible to adjust their surface-active properties with respect to the gas-liquid interface and, consequently, the ability to remove the kinetic restriction to the formation of flotation contact. The physical form of sorption on a mineral can be represented by collector sediments and ion-molecular associates. The research results show that when the interlayer breaks through, these forms can desorb from the mineral and spread over the bubble surface, dragging the liquid from the interlayer into motion, thereby “drying” the mineral surface. In turn, the removal of liquid from the interlayer leads to a reduction in the induction time, which affects the efficiency of flotation. The results make it possible to reveal the mechanism of flotation activation with heavy metal salts and can be used in the development of fundamentally new engineering solutions.

DETERMINATION OF THE DEPENDENCE OF THE SIZE OF THE FLOATED PARTICLES ON THEIR PROPERTIES AND THE HYDRODYNAMICS OF THE FLOTATION CHAMBER

It is noted that medium-sized particles have the highest flotation rate. Grains of the boundary classes of the size range have a reduced floatability, and they account for more than 50% of all losses of extracted minerals during flotation. The stability conditions of the particle - bubble flotation unit in the chamber of the foam flotation machine are considered. The effect of perturbations of the bubble surface on the size of the floated particles is studied. The amplitude of the initial deformation of the surface and the amplitude of the initial deformation rate of the bubble surface were determined depending on the energy of the turbulent pulsations of the environmental liquid. It is established that the rate of energy dissipation in the chamber of the flotation machine has a moderate effect on the size of the extracted grains. The influence of the surface properties of mineral particles and their mass on the upper value of the particle size range is studied. It is shown that the hydrophobicity of the surface has a significant effect on the size of the mineral particles that remain in contact with the gas phase. The main parameter that characterizes the effect of the hydrophobicity of the surface of the floated particles on the value of the separation force can be the value of the advancing contact angle.