Energetics and structures of hydrogen-vacancy clusters in tungsten based on genetic algorithm

The behavior of hydrogen （H） in metals has been a long- standing research topic in materials science. One of the most compelling subjects is the deleterious effects of H on the microstructural evolution of materials; these effects include H embrittlement, superabundant vacancy formation, and blistering. Vacancies have been demonstrated through both experiments and computational simulations to have strong H trapping effects [1], resulting in increased H retention [2], gas-filled bubble formation [3-5], and surface modification [6-9]. In addition, at high temperatures and high H pressures, superabundant vacancy formation induced by H is observed [ 10,11 ]. Unfortunately, even though substantial research has been conducted on the interplay between H and vacancies [12-14], the detailed processes by which H-vacancy com- plexes nucleate, grow, and agglomerate remain unclear. In these processes, the energetics and structures of H-vacancy clusters are undoubtedly important.

Recent studies of tungsten-based plasma-facing materials in the linear plasma device STEP

This contribution summarized the recent studies of tungsten-based plasma-facing materials in the linear plasma device like the simulator for tokamak edge plasma(STEP),focusing on the examination of newly developed tungsten(W)-based materi-als and plasma-induced defects in pure W.Pure W,W-V,W-Y_(2)O_(3)and W-ZrC samples were exposed to a high-flux plasma of~1021-1022 m^(−2)s^(−1) with a fluence up to 1026 m^(−2) at a surface temperature below 500 K.The investigation of fundamental evolution of plasma-induced defects in pure W indicated a critical role of hydrogen-dislocation interactions.Suppressed surface blistering was observed in all W-based materials,but deuterium desorption behavior and retention were distinct with respect to different materials.The studies showed that the linear plasma device like the STEP was indispensable in the understanding of plasma-material interactions and the qualification of new materials for future fusion reactors.

Preface to the special issue on plasma facing materials for fusion energy

International thermonuclear experimental reactor(ITER),the largest tokamak device so far,will operate with a full-tungsten divertor to handle the steady heat fluxes of 10 MW m^(−2),the slow transients of 20 MW m^(−2)(~10 s),as well as the transient heat fluxes up to~GM m^(−2)(<1 ms).Currently,tungsten(W)is also foreseen as the most suitable plasma-facing material(PFM)for the first wall in demonstration(DEMO)and future fusion reactors,as well as the divertor.The wall material in future fusion reactors must fulfill the requirements of sufficient lifetime,negligible or small long-term retention of tritium(T)fuel and an acceptable neutron activation level in long-term operation,which are favorable for W walls.

Formation of a disordered region at the grain boundary during migration with He atoms

W is considered a potential candidate as a plasma facing ma- terial for future nuclear fusion devices because of its high melting point, low sputtering rate, and low H or He solubility [1-3]. In a fusion environment, W will be in direct contact with heat flux, H/He particle fluxes, and the irradiation of high-energy neutrons, causing several defects to be generated, which decrease the service life of W materials. The grain boundary （GB）, which is an important type of defect, affects the various physical and mechanical properties of ma- terials. In the nuclear environment, the GB can act as a sink for the defects when the material is under irradiation.

Molecular dynamics simulations of temperature effect on tungsten sputtering yields under helium bombardment

Tungsten is the most promising plasma-facing material （PFM） for future nuclear fusion reactors such as international thermonuclear experimental reactor （ITER） owing to its high melting temperature, high thermal conductivity and low hydrogen retention. Under ITER-relevant conditions, a large amount of helium from the fusion reactions will constantly bombard the PFM. Though the energies of helium atoms in different regions are different,

The effect of hydrogen on the recombination of Frenkel pair in tungsten： A theoretical insight

Tungsten (W), with its primary advantages, is considered as the most promising candidate for plasma facing materials (PFMs) for the next generation of fusion devices such as ITER. However, continuous bombardment with 14.1 MeV neutron introduces Frenkel defects as the primary damage in W [1]. The Frenkel defects, composed of self-interstitial atoms (SIAs) and vacancies, can develop to extended defects such as voids and interstitial clusters, resulting in hardening, swelling and embrittlement of W, thus degrading the properties of W [2]. The recombination of SIAs and vacancies is an effective way to reduce the Frenkel defects in bulk W, which enhances the radiation resistance of W based on recent theoretical calculations [3,4]. The moving of the SIA to the vacancy could finish the recombination process through instantaneous or thermally activated way [3]. The instantaneous recombination region is an ellipse with the semi-minor axis of 5.4 ? and semi-major axis of 18 ? according to the molecular dynamics calculation [4].