Y.G. Li

Modulation of the thermodynamic, kinetic, and magnetic properties of the hydrogen monomer on graphene by charge doping

The thermodynamic, kinetic, and magnetic properties of the hydrogen monomer on doped graphene layers were studied by ab initio simulations. Electron doping heightens the diffusion potential barrier, while hole doping lowers it. However, both kinds of dopings heighten the desorption potential barrier. The underlying mechanism was revealed by investigating the effect of charge doping on the bond strength of graphene and on the electron transfer and the coulomb interaction between the hydrogen monomer and graphene. The kinetic properties of H and D monomers on doped graphene layers during both the annealing process (annealing time t(0) = 300 s) and the constant-rate heating process (heating rate α = 1.0 K/s) were simulated. Macroscopic diffusion of hydrogen monomers on graphene can be achieved when the doping-hole density reaches 5.0 × 10(13) cm(-2). Both electron and hole dopings linearly reduce the total magnetic moment and exchange splitting, which was explained by a simple exchange model. The laws found in this work had been generalized to explain many phenomena reported in literature. This study can further enhance the understanding of the interaction between hydrogen and graphene and was expected to be helpful in the design of hydrogenated-graphene-based devices.

Ab Initio Simulations of the Kinetic Properties of the Hydrogen Monomer on Graphene

The understanding of the kinetic properties of hydrogen (isotopes) adatoms on graphene is important in many fields. The kinetic properties of hydrogen-isotope (H, D, and T) monomers were simulated using a composite method consisting of density functional theory, density functional perturbation theory, and harmonic transition state theory. The kinetic changes of the magnetic property and the aromatic π bond of the hydrogenated graphene during the desorption and diffusion of the hydrogen monomer were discussed. The vibrational zero-point energy corrections in the activation energies were found to be significant ranging from 0.072 to 0.205 eV. The results obtained from quantum mechanically modified harmonic transition state theory were compared with the ones obtained from classical-limit harmonic transition state theory over a wide temperature range. The phonon spectra of hydrogenated graphene were used to closely explain the (reversed) isotope effects in the prefactor, the activation energy, and the jump fr...

Neutronics analysis for the test blanket modules proposed for EAST and ITER

The dual-functional lithium lead-test blanket module (DFLL-TBM) system, which is designated to demonstrate the integrated technologies of both the He single coolant (SLL) blanket and the He-LiPb dual coolant (DLL) blanket, is proposed for testing in ITER to check and validate the feasibility of the Chinese LiPb blankets. Considering the conflict between the limited ITER resources for TBM testing and the requirement of various blanket concepts proposed by the parties, EAST, the superconducting tokamak being operated in China, can serve as a valuable pre-testing platform with some comparable design parameters to ITER for DFLL-TBM. In the contribution, neutronics calculations and activation of the TBMs in EAST are carried out and compared with those in the D–D and D–T phase of ITER. The results from EAST can make an analogy to ITER (to some extent).

AN IMPROVED CLUSTER DYNAMICS MODEL FOR HYDROGEN RETENTION IN TUNGSTEN

An improved cluster dynamics model has been developed for studying the behaviors of hydrogen retention in tungsten under hydrogen ions irradiation. In addition to different types of objects, adopting up-to-date parameters and complex reaction processes, we newly introduce ion-induced and natural defects into our model. This improved model programmed in IRadMat2 could describe very well the depth distributions and the amounts of hydrogen retained in tungsten under different radiation conditions. The calculated results agree with the experimental ones much better than the previous model, especially for the depth-distribution of D retained in W, which imply that this model is applicable to the evolution of defects especially for low energy high flux ions irradiated on plasma-facing materials.

Creeping Motion of Self Interstitial Atom Clusters in Tungsten

The formation and motion features of self interstitial atom (SIA) clusters in tungsten are studied by molecular dynamics (MD) simulations. The static calculations show that the SIA clusters are stable with binding energy over 2 eV. The SIA clusters exhibit a fast one dimensional (1D) motion along 〈111〉. Through analysis of the change of relative distance between SIAs, we find that SIAs jump in small displacements we call creeping motion, which is a new collective diffusion process different from that of iron. The potential energy surface of SIAs implicates that the creeping motion is due to the strong interaction between SIAs. These imply that several diffusion mechanism for SIA clusters can operate in BCC metals and could help us explore deep insight into the performance of materials under irradiation.

First-principles investigation of the orientation influenced He dissolution and diffusion behaviors on W surfaces

The dissolution and diffusion behaviors of helium (He) for four low-Miller-index tungsten (W) surfaces [(110), (100), (112), and (111)] are systematically studied using the density functional theory to understand the surface-orientation-dependent He bubble formation. The results show that He accumulation on the surfaces is mainly affected by self-trapping and the formation of He-induced vacancies. He-induced vacancies tend to form on the surfaces of W(111), W(100), and W(112) than in the bulk. Specifically, for the W(111) surface, He accumulation is facilitated by the high activation barrier arising from He-induced vacancy trapping, whereas the W(110) surface is resistant to the formation of He bubbles because of the higher vacancy and He formation energies. Our results are helpful for understanding the orientation dependence of surface damage on the W surface under low-energy high flux He ion irradiation and designing irradiation-resistant plasma-facing materials.

Cluster dynamics simulation of deuterium retention behaviors in irradiated beryllium

The retention behaviors of deuterium (D) in beryllium (Be) are investigated using a spatially resolved cluster dynamics model under different irradiation conditions. The trapping effects of deuterium (D) in the forms of D atoms, D2 molecules and D with vacancy complex clusters (DmV) play the most important role in the behaviors of D retention in bulk Be under irradiation of 9 keV D ions. The fraction of D2 in the total D retention increases with the increase in ion influence, due to the chemical reaction rate enhancement between D atoms with high density. The increases in both ion incident angle and Be bulk temperature reduce the retention of DmV complex clusters by increasing the D desorption rate. In addition, the neutron synergistic irradiation changes the D retention profiles, especially in the recombination region, by introducing extra defect sinks. These results can improve the understanding of the mechanisms of D diffusion, accumulation and retention in irradiated Be.