Correlation of hardness and surface microcracking in ITER specification tungsten exposed at QSPA Kh-50

Bakaeva, A.; Makhlai, V.А.; Terentyev, D.; Zinovev, Aleksandr; Herashchenko, S.S.; Dubinko, A.

doi:10.1016/j.jnucmat.2019.04.008

Cited by 6 publications

(9 citation statements)

References 26 publications

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“…The transverse transformation of longitudinal cracks could be induced by longitudinal tensile stress and other factors, such as the direction of long grains parallel to the surface of the rolled sheet, and the inertia of motion during the formation of longitudinal cracks [27]. In addition, in the shaded zone of crack formation in figure 10(c), it can be noticed that the time when cracks started to form on the tungsten surface was later than those at about 110 µm depth, which meant that the cracks may preferentially sprout inside the material [35,54]. Figures 10(e) and ( f ) show the evolution of transverse stress and transverse plastic strain rate of molybdenum at 50 J cm −2 irradiation, respectively.…”

Section: Mechanical Simulation and Cracking Behaviormentioning

confidence: 99%

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Experimental and simulation studies on damage mechanisms of tungsten and molybdenum under compressed plasma flow irradiation

Zhang

et al. 2023

Nucl. Fusion

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The failure mechanism of plasma-facing components (PFCs) under extreme plasma conditions relevant for fusion reactor were investigated. Here, edge-localized mode (ELM)-like transient thermal shock irradiation experiments were performed on tungsten and molybdenum using compressed plasma flow, and combined with thermal-mechanical analysis by means of finite element simulations to discuss the grain structure evolution, cracking behavior and variations of hardness. When ELM-like thermal shock irradiation was sufficient to melt tungsten and molybdenum, submicron-sized cellular sub-grain structure created on their surface due to the high temperature gradient of the molten layer under the effect of the Bénard-Marangoni instability. Rapid directional solidification from the bottom of the molten layer to the surface induced the formation of columnar grains dominated by <200> orientation. While the formation of cellular sub-grains increased hardness, the thermal effect of irradiation and the formation of columnar grains led to softening. The high thermal stress induced by the ELM-like thermal shock produced macro-cracks and micro-cracks on the surface of tungsten and only micro-cracks on the surface of molybdenum. Macro-cracks generated due to the intrinsic brittleness of tungsten. As a result of stress evolution, longitudinal macro-cracks extending perpendicular to the surface experienced transverse transformation within the material. Micro-cracks formed due to the embrittlement of the re-solidification zone, and their width increased with the melting depth. These results help to understand failure mechanisms in PFCs under extreme operation conditions which are valuable for developing future fusion reactors.

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Section: Mechanical Simulation and Cracking Behaviormentioning

confidence: 99%

“…Softening occurred as soon as T max > T r . The thermal effect on the recovery of the microstructure [54] and the formation of columnar grains both probably reduced the hardness. It can be seen that the change in hardness after irradiation is the result of competition between several factors.…”

Section: Hardening and Softeningmentioning

confidence: 99%

Experimental and simulation studies on damage mechanisms of tungsten and molybdenum under compressed plasma flow irradiation

Zhang

et al. 2023

Nucl. Fusion

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“…Many research groups have used a coaxial gun to simulate the damage effect of ELM-I on the divertor wall material in tokamaks. The National Science Center Kharkov Institute of Physics and Technology (NSC-KIPT) not only studied the characteristics of plasma and PSI but also studied the characterization of the materials in detail using a self-developed piece of equipment called a quasi-stationary plasma accelerator (QSPA) [1,10]. NSC-KIPT also did other research on ITER with QSPA/QSPA-M.…”

Section: Introductionmentioning

confidence: 99%

Experimental study on plasma generated by a tapered coaxial accelerator and its damage effects on a tungsten target at different angles

Zhao¹,

Chen²,

Song³

et al. 2022

Plasma Phys. Control. Fusion

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Plasma wall interaction (PWI) will occur inevitably during the operation of Tokamak. The coxial gun device has low operation cost and parameters of plasma produced by the gun are close to those of type I ELM, therefore, the coaxial gun is suitable in simulation experiment as heat-flux sources of transient events such as type I ELM under the condition of H-mode in ITER. In this paper, the plasma generated by the discharge of a tapered coaxial accelerator thermal shock on a tungsten target to simulate the damage effect of the divertor. The plasma parameters are measured in the experiment. The velocity of the plasma is 41.7 km/s, and the kinetic energy of a single hydrogen ion is 9.2 eV. The energy density at the center of the plasma can reach 1.5 MJ/m2, and the density can reach about 2.78×1015 /cm3. The reflection of plasma in the process of exposure at different angles is observed. It is observed that droplets of millimeter size splash from the target. Traces of liquid flow are observed on the surface of the target, which shows that there is a melting process on the surface of target. The mass loss of the target is in the order of mg after 20 pules. The ablation and residual stress of the target surface both decrease with the decrease of the angle. This is because the accumulated energy per unit area of the target surface decreases with the decrease of the angle. These results help us to better understand the damage effect of tungsten target for further research.

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“…Experimental simulations of high-energy fluxes expected in fusion reactors are carried out in presently available fusion devices such as ASDEX Upgrade, JET or Large Helical Device (LHD) [1,3]. Furthermore, simulation experiments are also performed using linear and e-beam facilities, pulsed plasma guns, powerful quasi-stationary plasma accelerators (QSPA) as test-bed facilities [4][5][6][7][8][9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

“…Even the loads, which are twice less than the melting energy threshold led to the appearance of fatigue cracks already after 100 plasma pulses. In this case, the cracks initiation could be caused by an accumulation of the stress-induced lattice defects which harden the material in plasma-affected thin sub-surface layer [7][8][9]. Analysis of experimental data confirms that the origin of crack formation could be attributed to the plastic deformation of surface layers by the twinning mechanism.…”

Section: Introductionmentioning

confidence: 99%

Damaging of Pure Tungsten With Different Microstructure Under Sequential Qspa and LHD Plasma Loads

Herashchenko¹,

Byrka²,

Makhlaj³

et al. 2020

Problems of Atomic Science and Technology

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The cracking thresholds were evaluated for tungsten samples with different microstructure in the course of QSPA Kh-50 repetitive plasma loads. No damage has been observed on the exposed surfaces under 0.1 MJ/m2. Nevertheless, cracks were detected in the bulk of irradiated tungsten (with longitudinal grain orientation). Increasing heat load up to 0.2 MJ/m2 caused the damaging of all types of tungsten targets. The observed cracks propagate to the bulk mainly transversely and parallel to the irradiated surface. The effect of the subsequent exposure with LHD divertor plasma on the tungsten samples was analyzed. The obtained results are discussed.

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Correlation of hardness and surface microcracking in ITER specification tungsten exposed at QSPA Kh-50

Cited by 6 publications

References 26 publications

Experimental and simulation studies on damage mechanisms of tungsten and molybdenum under compressed plasma flow irradiation

Experimental and simulation studies on damage mechanisms of tungsten and molybdenum under compressed plasma flow irradiation

Experimental study on plasma generated by a tapered coaxial accelerator and its damage effects on a tungsten target at different angles

Damaging of Pure Tungsten With Different Microstructure Under Sequential Qspa and LHD Plasma Loads

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