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Yang, L.

Publications and source records attributed to Yang, L..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Perspectives on multiscale modelling and experiments to accelerate materials development for fusion

Prediction of material performance in fusion reactor environments relies on computational modelling, and will continue to do so until the first generation of fusion power plants come on line and allow long-term behaviour to be observed. In the meantime, the modelling is supported by experiments that attempt to replicate some aspects of the eventual operational conditions. In 2019, a group of leading experts met under the umbrella of the IEA to discuss the current position and ongoing challenges in modelling of fusion materials and how advanced experimental characterisation is aiding model improvement. This review draws from the discussions held during that workshop. Topics covering modelling of irradiation-induced defect production and fundamental properties, gas behaviour, clustering and segregation, defect evolution and interactions are discussed, as well as new and novel multiscale simulation approaches, and the latest efforts to link modelling to experiments through advanced observation and characterisation techniques.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Measurement of the scintillation and ionization response of liquid xenon at MeV energies in the EXO-200 experiment

In this work, liquid xenon (LXe) is employed in a number of current and future detectors for rare event searches. We use the EXO-200 experimental data to measure the absolute scintillation and ionization yields generated by γ interactions from 228 Th (2615 keV), 226 Ra (1764 keV), and 60 Co (1332 keV and 1173 keV) calibration sources, over a range of electric fields. The W value that defines the recombination-independent energy scale is measured to be 11.5±0.5 (syst.) ±0.1 (stat.) eV. These data are also used to measure the recombination fluctuations in the number of electrons and photons produced by the calibration sources at the MeV scale, which deviate from extrapolations of lower-energy data. Additionally, a semiempirical model for the energy resolution of the detector is developed, which is used to constrain the recombination efficiency, i.e., the fraction of recombined electrons that result in the emission of a detectable photon. Detailed measurements of the absolute charge and light yields for MeV-scale electron recoils are important for predicting the performance of future neutrinoless double β -decay detectors.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Determination of the cluster-decay branching ratio from a near-threshold molecular state in Be10

A puzzle has long existed for the α-cluster content in the near-threshold 7.54-MeV state of 10Be. A new measurement was conducted to measure the cluster-decay partial width of this state using the reaction 9 Be( 9 Be, 10 B *→α+ 6 He) 8 Be at 45-MeV beam energy. Special measures were taken to reduce the strong near-threshold background. Additionally, the neutron-decay strength was also obtained based on the threefold coincident measurement. A cluster-decay branching ratio of ( 4.04 ± 1.26 ) × 10 -4 is obtained, resulting in a reasonably large α -cluster spectroscopic factor. The present Rapid Communication confirms the formation of the σ -bond molecular rotational band headed by the 6.18-MeV state in 10 Be .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

A new cryogenic apparatus to search for the neutron electric dipole moment

A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). This apparatus uses superfluid 4 He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallation Neutron Source at Oak Ridge National Laboratory, uses polarized 3 He from an Atomic Beam Source injected into the superfluid 4 He and transported to the measurement cells where it serves as a co-magnetometer. The superfluid 4 He is also used as an insulating medium allowing significantly higher electric fields, compared to previous experiments, to be maintained across the measurement cells. Finally, these features provide an ultimate statistical uncertainty for the EDM of 2-3× 10 -28 e-cm, with anticipated systematic uncertainties below this level.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Mobility of tungsten clusters on tungsten surfaces

It is reported on an accelerated molecular dynamics investigation of surface transport mechanisms on W surfaces. These mechanisms likely influence the formation of nano-fuzz in fusion plasma-facing conditions. The simulations use an embedded-atom potential to investigate the diffusion mechanisms of W clusters (W n , n = 2–9) on W(1 1 0) and W(1 0 0) surfaces at 1000 K, reaching timescales beyond 10 microseconds. A number of fast moving adatom species, W n (n = 2–6), were observed. In contrast, slightly larger clusters W n (n = 7–9), especially W 8 , exhibit significantly lower diffusivities. The diffusion mechanisms of W n clusters on the W(1 1 0) surface are complex, with the most common elementary steps involving hops of monomers and dimers. Moreover, we observe tetramer hopping in the diffusion processes of W n (n = 4–7), trimer hopping in W n (n = 5, 6, 8), and pentamer hopping in W 5 on the W(1 1 0) surface. W n (n ≤ 3) and metastable W n (n > 3) clusters on the W(1 0 0) surface diffuse predominantly through monomer exchange with surface atoms. However, W clusters containing square tetramers are essentially immobile on the W(1 0 0) surface at 1000 K.

Instruments & Instrumentation↗
DOE OSTI2019

First-principles study of hydrogen diffusion and self-clustering below tungsten surfaces

The diffusion and self-clustering nucleation behavior of hydrogen (H) without vacancies below tungsten (W) surfaces are important for understanding the retention of deuterium (D) in W crystals exposed to high-flux and low-energy D plasma. The H migration energy and binding energy of H to self-clusters near the W(100), W(110), and W(111) surfaces have been investigated by first-principles computer simulations using density functional theory. H diffusion from adsorption sites on the W(100), W(110), and W(111) surfaces into solute sites in the bulk requires energies of at least 1.21, 1.78, and 1.80 eV, respectively, while 0.27, 0.31, and 0.24 eV for the reverse process. In addition, the lateral diffusion of H between two subsurface layers below the W surfaces has been investigated. Two H atoms at a depth of 0.08 nm below the W(110) surface have the highest binding energy, followed by H atom pairs below the W(111) and W(110) surfaces. The nucleation and stability of H clusters depend on the surface orientation. A planar configuration between the first nearest neighbor {100} planes is energetically favorable for H self-clustering below the W(100), W(110), and W(111) surfaces. In conclusion, the thermal stability of a platelet containing 16 H atoms below the W surfaces at 300 and 600 K was also studied by ab initio molecular dynamics simulations, which indicate that the H platelet below a W(111) surface is more stable than that below either the W(100) or the W(110) surface.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Effect of interatomic potential on the energetics of hydrogen and helium-vacancy complexes in bulk, or near surfaces of tungsten

Hydrogen (H) trapping by helium-vacancy (He$-$V) complexes in bulk and the near surface region of tungsten (W) have been investigated by molecular statics calculations that evaluate two different W$-$H interatomic potentials, which use the same W$-$He, He$-$He and He$-$H potentials. One of the W$-$H potentials is a bond-order potential (BOP) developed by Juslin et al., while the other is an embedding atom method (EAM) potential developed by Wang et al. Both potentials overestimate the H binding energies to He clusters in bulk W, as compared to DFT calculations, but properly predict the functional form of the H binding energies to He clusters with increasing number of He and H. The BOP simulations reveal that H binding energies to He x V complexes generally increase with increasing number of He. However, the EAM results indicate that the H binding energy as a function of number of He depends on the number of H, and the H binding energies change slightly at high He content. Compared with available DFT data, both BOP and EAM underestimate the H binding energies to He x V 2 H m complexes. Here, the BOP reproduces the He formation energy below a W surface, while the EAM potential better reproduces the H formation energy and the interactions between H and He$-$V complexes. Based on these comparisons, we determine that the EAM potential is more accurate than BOP for large-scale molecular dynamics simulations of W$-$He$-$H interactions. The EAM potential predicts that the difference in the average binding energies of H to stable He$-$V complexes near the W surface is less than 0.2 eV and the difference decreases with increasing He content. Thus, the EAM potential indicates that the effect of surfaces on H binding energies to large He$-$V complexes below the W surfaces can be ignored.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Total dose effect of Al 2 O 3 -based metal–oxide–semiconductor structures and its mechanism under gamma-ray irradiation

In our work, insights into the total dose response and native point defect behavior in the Al2O3 gate dielectric during irradiation were gained by gamma-ray irradiation experiments and first-principles calculations. It is found that the O vacancy (VO) can act as a hole trap in the Al2O3 gate dielectric during irradiation, leading to the negative shift of the capacitance–voltage (C–V) curves of the Al2O3-based metal–oxide–semiconductor (MOS) structure. Our calculations show that the neutral defect VO becomes a +2 charged center after irradiation, and the positively charged VO is a kind of conductive path for electrons, which contributes to an increase of the leakage current in the irradiated MOS capacitors. Additionally, the trapped holes are accumulated with irradiation doses, which can lower the barrier height of the Al2O3 gate oxide and further cause the increase of the leakage current. The other native point defects in the Al2O3 layer, such as aluminum vacancy (VAl), aluminum interstitial (Ali) and oxygen interstitial (Oi), only act as fixed charge centers during irradiation. Net negative charges existing in the Al2O3 layers before irradiation are mainly induced by the negatively charged defects of VAl and Oi.

Engineering↗