Beryllium Surface Research Articles

Angular momentum and lithium transport from main sequence to sub-giant and red giant low-mass stars

Context. Asteroseismology provides a unique opportunity to probe the interiors of evolved stars and constrain their internal rotation. The correct reproduction of the core rotation evolution has not yet been achieved, although it is key to understanding the internal processes involved in low-mass stars. Aims. We explore the efficiency required to reproduce the general behaviour of the transport of angular momentum along the evolution in view of asteroseismic constraints from giant low-mass stars. We analyse the consequences and predictions for lithium and beryllium surface abundances from the main sequence to red giant phase. Methods. We computed a series of models, which included atomic diffusion, rotation-induced mixing, magnetic braking, and additional processes tailored for main sequence low-mass stars. We extended these models to more evolved phases and investigated an updated angular momentum transport by including a time-dependent extra viscosity related to the azimuthal magneto-rotational instability. We compared our predictions to the asteroseismic measurements of the core and surface rotation of a sample of sub-giant and red giant stars. We compared the model predictions for the lithium and beryllium surface evolution with the available observations. Results. We confirm that a time-dependent additional viscosity νadd(t) is required to reproduce the general behaviour of the core rotation rate along successive stellar evolutionary phases given the dependence on the differential rotation and the mass. We show that it results in stronger lithium and beryllium depletions for low-mass stars over evolution. We confirm that predicted lithium abundances at the red giant bump by classical models, commonly used as references, cannot reproduce the lithium depletion along the main sequence and evolved phases of stellar evolution. We show that the observed amount of lithium of stars less massive than 1 M⊙ leads to a discrepancy between model predictions and observations at the red giant bump. Conclusions. We show that a semi-parametric model can reproduce the rotational behaviour along the first phases of evolution well, with the exception of the sharp transition observed during the sub-giant phase. This suggests that two distinct transport processes may be involved. The processes required to transport chemicals during the main sequence phase and angular momentum until the red giant phase impact the lithium depletion all along the evolutionary duration. A good prediction of the lithium abundance at young phases places strong constraints on the predicted one at more evolved phases. It also highlights discrepancies between models and observations for the lowest mass stars and impacts the threshold that defines lithium-rich giant stars, showing that classical models tend to overestimate this threshold.

Detritiation of JET Beryllium and Tungsten

During the operation of a fusion reactor, first wall components are exposed to the plasma and therefore tritium, resulting in generation of tritiated materials that would be classified as intermediate level waste (ILW) following their removal from the vessel. Investigations were undertaken into the thermal treatment of beryllium and tungsten representative of the materials used within the Joint European Torus (JET) fusion reactor to assess if tritium from these materials can be removed in the Material Detritiation Facility at the United Kingdom Atomic Energy Authority. This detritiation process may allow the reclassification of these materials as low level waste (LLW). When heated in the presence of oxygen, both tungsten and beryllium readily oxidize as temperature increases. The oxide layers that are formed on tungsten and beryllium surfaces are thought to act as a tritium barrier, reducing the amount of tritium that can be removed by thermal treatment. As such, the generation of oxide layers may need to be minimized for treatment of tungsten and beryllium, potentially via thermal treatment at lower temperatures. Additionally, the formation of beryllium oxide presents health and safety concerns due to its toxicity and physical form. Experiments were undertaken using tungsten and beryllium samples from previous JET campaigns. The samples were heated in a pyrolyzer, and the tritium released was captured in a series of bubblers. The remaining tritium in the material was characterized by acid dissolution to allow for detritiation factors (which are defined as the fraction of tritium inventory in the sample before and after the thermal treatment) to be calculated. Tritium was successfully removed from the samples by thermal treatment in air. Future trials will use samples with larger tritium inventory to confirm obtained results and demonstrate the feasibility of thermal treatment as a detritiation method for tungsten and beryllium on higher-activity samples. This should allow for samples representative of the JET ITER-like wall (current JET configuration) to be detritiated and could demonstrate the ability of the process to reduce the tritium inventory of JET materials and allow reclassification of components from ILW to LLW.

INVESTIGATION OF THE RADIATION-THERMAL OXIDATION OF BERYLLIUM IN THE SYSTEM Be-WATER BY THE METHODS OF INFRARED AND OPTICAL SPECTROSCOPY

Radiation-thermal oxidation of beryllium in contact with water at temperatures T = 473…773 K under the combined effect of temperature and gamma radiation has been studied by methods of infrared and optical spectroscopy. The formations of an oxide layer on the surface of beryllium were traced from the infrared and optical reflection spectra. In the IR spectra, the broadening of the oxide layer on the Be surface (T = 573 K) was revealed with an increase in the absorbed dose by ~ 2.5 times, which is associated with inhomogeneities caused by gamma irradiation. According to the optical reflection spectra of the surface of radiation-thermally oxidized Be, it was revealed that in the region of the edge of short waves λ ≤ 250 nm, an absorption band is observed, the intensity of which increases with increasing contact time and indicates the formation of an oxide layer

Photothermal Determination of the Surface Treatment of Cd1-xBexTe Mixed Crystals

Cd1−xBexTe, a new material with potential for X-ray and γ-ray detectors, was analyzed by photothermal piezoelectric spectroscopy. The samples were tested depending on beryllium content and surface preparation. The main aim of the measurements was to extract the energy gap values, which were found for x = 0.01, 0.03, 0.05, and 0.1. It was shown that mechanical (polishing) and chemical (etching) treatment strongly influenced the amplitude and phase spectra of CdBeTe crystals. Piezoelectric spectroscopy allowed for comparing the quality of preparation of both surfaces for a single sample. The sub-surface damaged layer that was created as a result of surface processing had different thermal parameters than the bulk part of the sample. It was responsible for the additional peaks in the amplitude spectrum and changes in the phase spectrum of the photothermal signal. Two different methods of sample etching were analyzed. One completely quenched the signal, and the other did not eliminate the defects present on the surface after the cutting process. The article presents the preliminary interpretation of experimental data using the modified Blonskij model.

Beryllium dust generation caused by HHF tests

Beryllium will be used as a plasma-facing material of the ITER reactor components. One such component is the ITER first-wall panel, which contains a layer of beryllium tiles on the plasma-facing surface. Full-Scale Prototypes (FSP) of these panels are undergoing qualification through a series of cyclic High-Heat-Flux (HHF) tests at the HELCZA (High Energy Load Czech Assembly) facility. Such process, directly and indirectly, causes disintegration of the beryllium surface and results in beryllium dust formation. With regards to the beryllium toxicity, it is crucial to monitor the occurrence and the spread of the mentioned dust to ensure personnel safety. Moreover, it is necessary to decontaminate FSPs from the beryllium dust at the end of HHF tests. This study deals with the monitoring of the beryllium dust concentration levels on the FSP after HHF testing at HELCZA and its spread to the vicinity of the testing area, with the aim to provide a basis for safe operation.

Numerical estimation of the atomic fraction during laser-induced desorption of hydrogen from tungsten and beryllium

Monitoring of the DT-fuel retention in plasma-facing components (PFCs) is vital for long-term operations of future fusion devices. Laser-induced desorption (LID) is a proposed technique for the systematic in-situ control of hydrogen isotope content in surface layers of PFCs. An accurate interpretation of LID measurements requires information on the composition of released particles. Under some conditions, both atoms and molecules can be desorbed. The present study aims to verify the role of hydrogen atomic release under nanosecond and millisecond laser pulses. After investigation of general trends, we carried out the detailed analysis of hydrogen desorption from clean tungsten and beryllium surfaces, assuming a uniform distribution of hydrogen in a 10 μm layer with 1 at.% of initial content. Calculations were based on a common reaction-diffusion model supplemented by rate equations of molecular and atomic desorption. As a result, the atomic fraction is estimated to reach ∼40% during ms-heating of tungsten to near-melting temperatures, and less than 10% in the ns-case. Regarding beryllium, molecular recombination is shown to be the main process of hydrogen desorption in both heating scenarios.

Influence of Hydrogen Plasma on the Surface Structure of Beryllium.

This paper presents the research results of hydrogen plasma effect on the surface structure of the TGP-56 beryllium. In the linear simulator, the operating conditions of the first wall of ITER are simulated. Beryllium was irradiated with hydrogen plasma at surface temperatures of ~360 °C, ~800 °C, and ~1200 °C, depending on its location in the ITER chamber; with a different number of pulses with a duration of each pulse of 500 s. Samples of irradiated beryllium were subjected to a set of material studies. Experimental data were obtained on the change in the structure of the surface and edges of the beryllium samples after the plasma effect. It was found that at normal (2 MW/m2) and increased (4.7 MW/m2) heat fluxes on the first wall of the ITER, the edges and beryllium surface have good resistance to erosion. Under critical conditions close to the melting point, beryllium strongly erodes and evaporates. It has been established that this material has a high resource resistance to hydrogen plasma effect in the ITER under operating conditions.

Microstructural analysis of the thermal fatigue tested Be/CuCrZr joint with artificial defects between Ti/Cu interlayers

The ITER enhanced-heat-flux (EHF) FW fingers undertook by China are made by hot isostatic pressing (HIP) method to bond beryllium armor tiles to CuCrZr/316L(N) heat sinks with 10 μm-thick Ti coating on beryllium tiles and 0.5 mm-thick oxygen free copper sheet as interlayer. To study its thermal fatigue behavior, small scale mock-up was manufactured with artificial defects (AD) on the beryllium tile surface with Ti coating. Thermal cycling of the mockup was carried out at 4.7 MW/m2 high heat flux (HHF) for 5000 cycles. The interface between Be/Ti/Cu and the fracture surface on beryllium tiles were observed by stereomicroscopy and scanning electron microscopy with energy spectrometer. The Be/Ti/Cu interfacial phase composition and the behaviors of defects after high heat flux test were analyzed. In addition, the generation and propagation mechanism of thermal fatigue defects were preliminarily studied in this paper. The results show that uniform bonding between Be and Cu was achieved and the interfacial phases are Be base/ Be-Ti intermediate/ α-Ti/ Ti2Cu/ TiCu /Cu base in the sequence. The formation of complex brittle phases reported in previous study, such as Ti3Cu4 or α-TiCu4, can be avoided by using Ti single interlayer. When the original defect dimension is only 3 × 3 mm2, the defect will not propagate after 5000 cycles 4.7 MW/m2 HHF testing (HHFT). Besides, decreasing beryllium tile size can reduce the possibility of thermal fatigue failure. In addition, from the research on fracture surface on beryllium tiles, the final fracture made for beryllium detachment mainly happened in Ti layer near the beryllium side. While thermal fatigue cracks preferentially originated at Be/Ti interface and the oxidation of beryllium surface under thermal cycling test would accelerate the generation and propagation of thermal fatigue defects.

Sputtering and reflection from a beryllium surface: effects of hydrogen isotope mass, impact position and surface binding energy

Atomistic simulations with machine-learned potential energy functions are employed for understanding the mechanisms driving the sputtering of beryllium by low-energy deuterium and tritium atoms and the details of their retention on pristine beryllium surfaces. The interaction between hydrogen/deuterium/tritium and beryllium surfaces regarding erosion yields is investigated by molecular dynamics simulations. The erosion yields of both hydrogen isotopes are similar for the same kinetic energies. Concentrating on deuterium, its impact on specific surface sites is analyzed. Finally, analytical expressions are used to predict the energy spectra of sputtered atoms.

Effect of pre-irradiation on corrosion performance of beryllium in BEPC II/BES III and CEPC beam pipe

Beryllium is one of the most important materials in high energy physics and nuclear physics experiments. Beam pipe, which lies at the centre of the second-generation Beijing Electron Positron Collider (BEPC II) and its detector Beijing Spectrometer III (BES III), is made of beryllium and the electron–positron beam collision occurs in it. China is planning to build a Circular Electron Positron Collider (CEPC) with higher brightness, in which the beryllium beam pipe will inevitably be used. High-speed particles will produce a lot of γ-rays and neutron irradiation and heat loads on the beryllium beam pipe in the collision. In order to ensure the normal particle detection of BES III, a coolant must be used to take away the excess heat to maintain the constant temperature of the outer wall of the beam pipe. Researches, however, have shown that the coolant can cause some corrosion of beryllium and affect the normal operation of the beam pipe in the irradiation environment. Therefore, this paper intends to study the influences of different irradiation types and doses on the corrosion performance of beryllium in EDM-1, by using No.1 Electrical Discharge Machining Oil (EDM-1) to scour the beryllium sample after γ and neutron pre-irradiation, according to the working condition of BEPC II/BES III. It is found that pre-irradiation promotes the formation of pitting nuclei and corrosion holes on the beryllium surface. The corrosion effect of γ pre-irradiation on beryllium in EDM-1 is much more significant than that of γ and neutron pre-irradiation and the corrosion strengthens with the increase of irradiation dose. Impurity elements in beryllium play an important role in inducing pitting corrosion and promoting the formation and expansion of corrosion holes. S2− in EDM-1 may adsorb on the surface and further be oxidized to SO2 and SO42−, which can be incorporated into the oxide–metal interface and change its composition. In conclusion, irradiation enhanced the corrosion of beryllium in EDM-1.

Modelling the sputtering and reflection from a beryllium surface: atomistic analysis

Sputtering from plasma-facing surfaces upon particle impact can limit the lifetime of components in fusion devices, especially in the diverter region. Atomistic simulations of the processes associated with plasma–wall interactions allow for a detailed analysis of sputtering, reflection and adsorption. Most former works of beryllium sputtering by hydrogen isotopes were aimed mostly on the sputtering yield. We investigate the influence of impact energy and angle on sputtering, and analyze these quantities also for the outgoing particle. We model the sputtering by non-cumulative molecular dynamics simulations with a large number of trajectories for the various parameters. The underlying forces and energies are obtained from high-dimensional neural networks fitted to density functional calculations. We find a good agreement with the previously reported sputtering yields for perpendicular impact and a qualitative accordance with experimental data. In detail, the sputtering yield increases with increasing impact energy for angles of incidence larger than 45° with respect to the surface normal, while smaller angles show a maximal yield up to 100 eV. In cases where D reflection rather than sputtering occurs, a similar pattern is found for all angles, with the maximal reflection rate at 80°.

Scale Symmetry of Stochastic Surface Clustering under Plasma Influence in Fusion Devices

Titanium, tungsten, carbon, lithium, and beryllium surface structure were analyzed after plasma irradiation in fusion devices. Exceptional extreme high-temperature plasma load in fusion devices leads to specific surface clustering. It is strictly different from any other conditions of material’s clustering. The hierarchical granularity with cauliflower-like shape and surface self-similarity have been observed. Height’s distribution is deviated from the Gaussian function. The relief roughness differs qualitatively from the ordinary Brownian surface and from clustering under other conditions. In fusion devices, the specific conditions regulate material surface clustering faced to plasma. Ions and clusters melt on the surface and move under the effect of stochastic electromagnetic field driven by the near-wall turbulent plasma. In such a process, long-term correlations lead to the growth of surface with a self-similar structure. The multiscale synergistic effects influence the self-similarity–fractal growth from nanometers to millimeters. Experimental results illustrate universality of stochastic clustering of materials irradiated with plasma in fusion devices.

Influence of helium ion irradiation on the morphology and microstructure of CN-G01 beryllium

Beryllium is considered as a candidate of ITER first-wall (FW) armor and neutron multiplier in fusion reactors. To assess the irradiation resistance of CN-G01 beryllium, which has been accepted as an alternative ITER-grade beryllium in China, 180 keV helium ions with fluences of 1.0 × 1017 ions cm−2, 5.0 × 1017 ions cm−2 and 1.0 × 1018 ions cm−2 were implanted at room temperature. The theoretical simulation of energy loss, damage distribution and helium concentration were proceeded by SRIM. In this paper, we report the experimental exploration of ion fluence effect on surface morphology and microstructure of irradiated samples. Field Emission Scanning Electron Microscope (FESEM) analysis depicted the formation and growth of helium bubbles at different irradiation ion fluences. No obvious exfoliation or cavities was observed on the surface at all ion fluences, suggesting a reliable radiation resistance of CN-G01 beryllium. Atomic force microscopy (AFM) morphology showed that the maximum height of bubbles was 47.8 nm. Surface roughness values increased slightly due to the formation of defects and bubbles on the irradiated beryllium surface. Nevertheless, the structural analysis demonstrated by grazing incidence x-ray diffraction (GIXRD), indicated an obvious preferred orientation on (101) peak at various ion fluences. Annihilation of defects caused by a small rise of the localized temperature could explain the increasing intensity of diffraction peak (101).

Assessment of multiscale hydrogen desorption models from (0001) Be surfaces

Beryllium is a proposed neutron multiplier material in future fusion devices like ITER and DEMO. As such, numerous studies of neutron-irradiated beryllium specimen have shown the appearance of facetted bubbles with considerable tritium accumulation at their (0001) surfaces. In this work, we thus simulate hydrogen isotope desorption from (0001) beryllium surfaces using a multiscale modeling approach. We first establish that very fast surface diffusion of hydrogen adsorbed in FCC and HCP sites can be studied independently from the bulk by means of static DFT calculations, as diffusion into the bulk is inhibited by multiple diffusion processes with an accumulated energy barrier of almost 3 eV. Static saddle point searching dimer DFT calculations also reveal energy barriers for associative desorption in a range between 0.94 eV and 1.52 eV due to varying amounts of co-adsorbed hydrogen isotopes in the immediate vicinity of the desorbing pair. A simple rate equation-based desorption model incorporating these associative desorption processes is constructed and compared to thermal programmed desorption (TPD) spectra of earlier exposure experiments. It is found that the simple rate equation-based desorption model seemingly already explains some characteristic aspects of the TPD spectra like a peak shift to lower temperatures by almost 100 K and considerable broadening with increasing coverage. To asses the merit of this model, a refined model effectively taking the repulsion among adsorbed hydrogen isotopes into account by means of relevant correlations from kinetic Monte Carlo (KMC) simulations using a cluster expansion (CE) truncation is considered as well. It is found that the simple model’s reproduction of characteristic features of experimental spectra is the result of error cancellation from considering an incomplete set of desorption processes on one hand and neglecting repulsion among adsorbed hydrogen on the other hand. We conclude that the experimental TPD spectra can not be fully explained by either of the two models and further research particularly considering additional adatoms like oxygen are necessary to understand the TPD spectra of the corresponding experiments.

Thermal Effect of Surface Catalysis in Subsonic Dissociated-Air Jets. Experiment on a High-Frequency Plasmatron and Numerical Modeling

Experiments on heat transfer in subsonic dissociated-air jets are performed on 100 kW VGU-4 induction plasmatron. The heat fluxes to the water-cooled surfaces of copper, silver, tantalum, beryllium, niobium, gold, molybdenum, and quartz are measured at the stagnation point on a cylindrical flat-nosed model, 50 mm in diameter, having rounded edges at 50 and 100 hPa pressures in the low-pressure chamber and the high-frequency (HF) generator power of 30 to 70 kW. At the same pressures and the HF generator powers of 45 and 64 kW the convective heating of a specimen of sintered silicon carbide is studied in the surface temperature range from 1720 to 1910 K. The predominance of the surface catalyticity effect on the heat flux with respect to nitrogen and oxygen atom recombination is demonstrated. Under the experimental conditions the air plasma flow in the discharge channel of the plasmatron, the subsonic jet flow past the cylindrical model, and the heat transfer to the stagnation point on the model are numerically simulated. Basing on the comparison of the experimental and calculated data on the heat fluxes to the surfaces of metals (Tw = 300 K), quartz (Tw = 572–722 K), and silicon carbide (Tw = 1720–1910 K) the quantitative catalyticity gradation of the materials considered with respect to heterogeneous recombination of nitrogen and oxygen atoms is established.

Reflection of Hydrogen Isotopes and Helium Atoms from the Surface of the First Wall of the ITER Tokamak

The reflection coefficients were calculated for the scattering of hydrogen isotopes and helium atoms from the surface of amorphous beryllium, carbon, and tungsten targets, which are of interest in the physics of thermonuclear plasma. The results demonstrate good agreement with the available experimental data. The isotope effect in the reflection of particles from the wall was analyzed. For the reflection of He atoms, a similarity in reflection coefficient versus Lindhard parameter curves was observed.

Observation of two-electron one-photon X-ray transitions in collisions of slow Xe26+ ions with beryllium surface

SynopsisTwo-Electron One-Photon (TEOP) X-ray transitions were observed for the first time in collisions of highly charged Xe ions with metallic Be surface. The intensities of TEOP X-rays are well described by performed MCDF for one-electron one-photon (OEOP) dipole-allowed transition of Paschen and Brackett series assuming constant TEOP/OEOP branching ratio. The importance of the Internal Dielectronic Excitation (IDE) in relaxation of hollow Xe ions/atoms has been evidenced and discussed.

Iterative training set refinement enables reactive molecular dynamics via machine learned forces.

Machine learning approaches have been successfully employed in many fields of computational chemistry and physics. However, atomistic simulations driven by machine-learned forces are still very challenging. Here we show that reactive self-sputtering from a beryllium surface can be simulated using neural network trained forces with an accuracy that rivals or exceeds other approaches. The key in machine learning from density functional theory calculations is a well-balanced and complete training set of energies and forces. We have implemented a refinement protocol that corrects the low extrapolation capabilities of neural networks by iteratively checking and improving the molecular dynamic simulations. The sputtering yield obtained for incident energies below 100 eV agrees perfectly with results from ab initio molecular dynamics simulations and compares well with earlier calculations based on pair potentials and bond-order potentials. This approach enables simulation times, sizes and statistics similar to what is accessible by conventional force fields and reaching beyond what is possible with direct ab initio molecular dynamics. We observed that a potential fitted to one surface, Be(0001), has to be augmented with training data for another surface, Be(011̄0), in order to be used for both.

Formation of beryllium-hydrogen ions in chemical sputtering from 20 to 420eV

Abstract The formation of BeD+ in collisions of deuterium molecular ions with a beryllium surface at hyperthermal energies is investigated, using a purpose-built tandem mass spectrometer setup, “SurfTOF”. In the manifold of products, hydrogen-containing molecules are of special interest in fusion devices. Our experiments show, that they can be formed in nearly all conditions comparable to plasma and wall temperature, with two mechanisms involved: First, BeD+ is formed directly in a reaction of the D2+ projectiles with the Be surface, which is the main aspect of this work. There was no evidence found, that this particular mechanism relies on D implanted in the bulk Be. BeD2+ was not detected. The second reaction pathway produces BeH+. It is efficiently formed when H2O molecules are adsorbed on the surface, much less abundant for hydrocarbon adsorbates. The yield of Be+, BeH+ and BeD+ products, is measured as a function of several parameters: Scanning the impact energy from 20 to 426 eV reveals that the molecular BeD+ is preferably produced at low energies. At 20 eV, its abundance is three times higher than that of pure Be+. When the surface temperature is raised from 298 to 673 K, sputtering yields increase two orders of magnitude for both, Be+ and BeD+.

Thermal desorption study of hydrogen isotopes trapping and its diffusion in tungsten coated with aluminum/beryllium layer during plasma irradiation

The influence of irradiation in hydrogen plasma with oxygen impurity on the penetration of hydrogen isotopes through the surface of tungsten, through the surface of beryllium and aluminum layers on tungsten, and through the tungsten-coating interface was studied. It was shown that all these processes are accelerated in the presence of oxygen impurity in plasma. A conclusion is made that detritisation of the surface of both in the conditions of a fusion reactor tungsten and beryllium is possible.