Growth mechanism of subsurface hydrogen cavities in tungsten exposed to low-energy high-flux hydrogen plasma

Chen, W.Q.; Wang, X.Y.; Chiu, Yu-Lung; Morgan, T.W.; Guo, Wangguo; Li, K.L.; Yuan, Yue; Xu, Bo; Liu, W.

doi:10.1016/j.actamat.2020.04.012

Cited by 22 publications

(11 citation statements)

References 40 publications

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“…Thus these dislocations turn out to be diffusive defects, which provides important support for the simulated large depth distribution of defect 1 in figure 9(a). The depth distribution of dislocations in [49] shows a decrease of concentration with depth, which supports our simulated depth distribution. In addition, considering the large exposure duration and fluence compared with that in [49], dislocations in this study are expected to reach an even larger depth.…”

Section: Blister-induced Dislocation-type Defectssupporting

confidence: 88%

Blister-dominated retention mechanism in tungsten exposed to high-fluence deuterium plasma

et al. 2020

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To investigate the effect of blistering on hydrogen isotope (HI) retention, a series of deuterium plasma exposures were performed using recrystallized tungsten samples at 500 K with high fluences up to 1.0 × 10 28 ions m −2 in the linear plasma device STEP. An increase of blister density and deuterium retention was observed with increasing plasma fluence. Based on the simulation of the thermal desorption spectra using TMAP, defects with different detrapping energies are found to be located at a depth of tens of microns, which coincides with the depth of the grain boundaries (GBs) close to the surface. The defect characterizations using transmission electron microscopy and positron annihilation Doppler broadening identified the defects as dislocation type and vacancy type, which were created by blistering. It is suggested that these defects can diffuse deep into the material, and the interaction between the diffusion of the defects and GBs causes a peculiar deuterium desorption spectrum over plasma fluences. Additionally, these blister-induced defects are the main source of deuterium retention. Regarding the effect of the blister-induced defects on deuterium retention, a blister-dominated retention mechanism is proposed to describe HI retention in conditions when blistering is severe as in this study. This investigation provides a new insight into the effect of blistering on retention and the modelling of retention in a tokamak edge plasma environment.

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Section: Blister-induced Dislocation-type Defectssupporting

confidence: 88%

Blister-dominated retention mechanism in tungsten exposed to high-fluence deuterium plasma

et al. 2020

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“…The yellow box illustrates the location of the FIB cut (not to scale) which is located at the laser spot edge. [7], supporting the assumption that these cavities are stress concentration spots.…”

Section: The Influence Of Blisteringsupporting

confidence: 62%

“…Owing to its high melting point, high thermal conductivity, low activation, low physical sputtering yields, and small fuel retention, tungsten is the chosen plasma-facing material for ITER, the world's largest fusion experiment [2]. However, tungsten undergoes a variety of microstructural changes under fusion plasma loads, such as hydrogen-induced blistering [3][4][5][6][7], helium-induced fuzz [8][9][10][11][12][13][14], recrystallization [15,16], and thermal fatigue [17][18][19][20][21]. Moreover, a strong interplay between these nano-and microscale mechanisms is expected because ITER will be operated in a staged approach [2].…”

Section: Introductionmentioning

confidence: 99%

Influence of porosity and blistering on the thermal fatigue behavior of tungsten

Li¹,

Vermeij²,

Hoefnagels³

et al. 2022

Nucl. Fusion

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Tungsten is the leading plasma-facing material (PFM) for nuclear fusion applications. It faces severe operating conditions, including intense hydrogen plasma exposure and high-cycle transient heat loading, which create various defects in tungsten. Additionally, defects have often already been introduced during manufacturing. Little is understood regarding the synergistic effect of such defects on the lifetime of tungsten so far. Here, we investigate the influence of porosity and blistering on the thermal fatigue behavior of tungsten. The pores resulted from powder metallurgy whereas the blistering was induced by hydrogen plasma exposure. Both conditions were subjected to transient heat loading by a high-power pulsed laser. The exposure was performed in the linear plasma generator Magnum-PSI, which closely mimics the expected particle and heat flux in the world’s largest fusion experiment, ITER. Both porosity and blistering degraded the fatigue resistance of tungsten. Pores tended to aggregate at high-angle grain boundaries (HAGBs) and assisted crack initiation therein, as revealed by focused ion beam (FIB) cross-sectioning and electron backscatter diffraction (EBSD) analysis. The blisters were characteristic of subsurface cavities, which were located at a depth close to the surface roughness induced by transient heat loading. The stress concentration at the tip of the cavities is considered to promote crack initiation. The results highlight the necessity of a ‘life cycle assessment’ of the tungsten PFM for nuclear fusion reactors.

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“…Then, these solute hydrogen atoms may be trapped at trap sites, or diffuse into bubbles, where hydrogen atoms combine into molecules that contribute to the growth of hydrogen bubbles. Loop punching is considered as a main mechanism of bubble growth in multiple metals and alloys including copper [32][33][34]. Loop punching is a form of plastic deformation.…”

Section: Model Descriptionmentioning

confidence: 99%

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

Cui¹,

Fan²,

Niu³

et al. 2021

Plasma Phys. Control. Fusion

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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 K–850 K with ion energy of 20–200 eV and irradiation fluence up to 1.0 × 1025 m−2. 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. 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.

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Growth mechanism of subsurface hydrogen cavities in tungsten exposed to low-energy high-flux hydrogen plasma

Cited by 22 publications

References 40 publications

Blister-dominated retention mechanism in tungsten exposed to high-fluence deuterium plasma

Blister-dominated retention mechanism in tungsten exposed to high-fluence deuterium plasma

Influence of porosity and blistering on the thermal fatigue behavior of tungsten

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

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