As noted above, most of the background gas in the accelerator originates from the ion source. Distances l2,R2 and angles α,θ in the SAC plane and real 3-D angles from origin to SAC2 shown for hall with simulator. It is due to the presence of the same object as in the one presented above.
Energy of maxima for the first peak of neutron pulses measured in the simulation experiment (MeV). It has been interpreted as a result of momentum (pressure) loss in the stochastic field line region [11, 12] or in the island divertor structure . On the one hand, without RMP (blue lines), the growth of the density leads to a sudden increase in the radiated power, see figure 3(b), and finally to radiative collapse of the entire plasma.
Density dependence of the emitted power measured by the bolometer (a), the emission of CIII (b), CIV (c), CV (d), and CVI (e) species measured by VUV spectrometer without (triangles) and with (circles) RMP. The most effective magnetic field configuration is toroidal in the shape of the doughnut.
The plasma-facing materials in fusion reactors will face very extreme conditions, such as high temperatures, high thermal loads, extreme irradiation conditions caused by high-energy neutrons, and high influences from high-flux, low-energy plasma. Tungsten is considered the most promising material for plasma-focused components (PFCs) in the magnetic confinement fusion devices, due to its high melting temperature, high thermal conductivity, low swelling, low tritium retention, and low sputtering yield. However, some major shortcomings, such as the irradiation brittleness and the high ductility-brittle transition temperature of pure tungsten, limit its application.
Among them, nanoparticle dispersion reinforcement such as oxide particle dispersion reinforced (ODS-W) and carbide particle dispersion reinforced (CDS-W) tungsten alloys and W fiber reinforced Wf/W composites are promising. The thermal load resistance of the material is also closely related to the strength and DBTT because the cracks will initiate when the thermal stress is greater than the ultimate strength of the material at temperatures above the DBTT or than the yield stress at temperatures below the DBTT [11-14]. In this sense, methods that clean impurities at GBs should be effective in improving the strength and ductility of tungsten.
Recent research results indicated that trace elements, such as Zr, Ti and Y, in tungsten can react with oxygen and reduce the influence of free oxygen on GBs by forming thermally stable nanooxide particles, thus purifying and strengthening the GBs, increasing the stability at high temperature [19-21]. Therefore, several approaches have been developed to improve the mechanical properties, such as increasing ductility and fracture toughness and reducing DBTT. First, tungsten materials with high strength and high thermal stability can be obtained by dispersing second-phase particles, such as oxides or carbides, forming the oxides or carbides and dispersion-enhanced (ODS or CDS) tungsten-based materials [22–30].
Recently, various ODS-W or CDS-W materials with increased strength and thermal stability have been fabricated and investigated for fusion applications [3, 30]. For example, W-La2O3 and W-Y2O3 showed improved strength, high recrystallization temperatures, and high thermal shock resistance. Carbides such as TiC, ZrC, and HfC have much higher melting temperatures than those of the aforementioned oxides and better compatibility with tungsten, which can lead to excellent all-around performance in CDS-W.
The low-energy and high-flux plasma radiation resistance of this W-ZrC alloy is better than that of W-La2O3, ITER grade pure W, and commercial pure W; the hydrogen retention is also lower than that of ITER grade pure W .
Oxide dispersion-strengthened W-based materials
At present, the performance of pure W can meet the service condition of ITER to a limited extent, but for CFETR and DEMO with higher working parameters, it is not enough. It is generally understood that the low ductility of tungsten is closely related to their poor grain boundary (GB) cohesion, due to the segregation of interstitial impurities, such as O in GBs [15, 16]. These refined grains and nanosized particles produce high density of GB/PB interfaces, which generate high strength and a promising radiation resistance.
To improve the ductility W-Y2O3 materials, various sintering and post-treatments, such as spark plasma sintering (SPS) and high-temperature sintering in combination with hot rolling or hot forging deformation were used [34–38]. The performance of these W-Y2O3 as potential plasma-turning materials was investigated in terms of microstructures, thermal physical properties, mechanical properties and thermal shock response when subjected to electron beam bombardment. For SPSed W-Y2O3, the tungsten grain exhibits an isotropic microstructure with an average grain size of 3.2 μm; the average of Y2O3 particles is about 80 nm .
Three-point bending tests indicated that the deformed W-Y2O3 had better mechanical strength and toughness. The determination of the thermal shock response revealed superior thermal shock resistance of the hot-rolled W-Y2O3 : no cracks but only surface roughness was found on the loaded surface after 100 shots at 0.6 GW/m2 for a pulse duration of 1 ms. The discrepancy in thermal shock response between the two materials and in particular the superiority of deformed W-Y2O3 agrees well with the results that the better the thermophysical and mechanical properties, the better the thermal shock resistance.
It is indicated that needle-like grains ranging from a few to more than 50 μm in wrought W-Y2O3 lead to improved mechanical properties . The tensile results have shown that it is a brittle fracture above 250°C and its strength is also less than that of the high energy velocity forgings , implying that bimodal interfaces (in forging) are more in favor of strengthening and formability. Therefore, it is important to note that again the design of the microstructure, here of hot forging, is at least as important as the ODS effect.
Due to the improved PB/GB interfaces from Zr, the strength and plasticity of this W-Zr-Y2O3 is further enhanced on the basis of W-Y2O3.
Carbide dispersion-strengthened tungsten-based materials
The rolled W-0.5ZrC showed higher strength and ductility than that of rolled W-0.5TiC  and rolled W-0.5TaC , which were fabricated after a similar process. Compared to the Plansee ITER W specification (IGP), AT&M ITER W specification (CEFTR), W-1wt%TiC (W1TiC), W-2wt%Y2O3 (W2YO) from the Karlsruhe Institute of Technology in Germany, and fine-particle W (FG) from the Institute of Higher Physics Plasma, W-0Bit in the Czech Republic. 51], as shown in figure 2. Mechanical properties of W-0.5ZrC alloy: (a) bending stress-strain curves tested at different temperatures (note that values greater than a bending strain of 15% are not accurate due to the limited bending angle of the machine).
Therefore, the excellent thermal shock resistance of rolled W-0.5ZrC seems reasonable as it has high strength, lower DBTT and good plasticity. The thermal fatigue behavior of as-rolled and recrystallized W-0.5ZrC alloys was investigated by repeated thermal shocks (100 shocks in total) with a pulse duration of 1 ms at RT . Nevertheless, there are still no thermal fatigue results of rolled W-0.5ZrC at higher core temperatures to be investigated in the near future.
The thickness of modified layers on W-0.5ZrC is much lower than that of pure W, W-La and W-Y1, which implies its better resistance to plasma irradiation and erosion . 58] also studied the evolution of morphology and thermal-mechanical properties of pure W, CVD-W and W-0.5ZrC alloys to pure H-beam and H/. The crack threshold of unexposed CVD-W is about ~0.22 GW/m2, a little lower than that of W-0.5ZrC.
After irradiation, the TDS results have shown that the rolled W-0.5ZrC exhibits much lower hydrogen retention than that of pure W as shown in Figure 7. Both the rolled W-0.5ZrC and pure W had a desorption peak at temperature around 560°C, and the peak intensity of W-0.5ZrC showed much lower than the co-extending detail of W-0.5Zr. scale interfaces in the rolled W-0.5ZrC sheet.
Thus, a large fraction of D atoms can escape from W-0.5ZrC during D plasma irradiation at 400 K, leading to low D retention in the materials.
W fiber-reinforced W f /W composites
Regarding the effect on the interfacial properties, the fracture energy of the Er/W multilayer and the ZrOx/Zr multilayer was affected by less than 10%, while it increased by 40% for the ZrOx/W bilayer. The single direction of W fibers can improve the fracture energy of tungsten matrix once the extrinsic hardening mechanisms of fiber pullout and plastic deformation are activated, but it will lead to the obvious anisotropy of mechanical properties . 74] used woven tungsten wire meshes as reinforcement in the composites (wire diameter, 127 μm; distance between wires, 1 mm), which avoided the anisotropy induced by unidirectionality of W fibers.
Additionally, a stable interfacial zirconia (ZrOx) layer was deposited on the grids by magnetron sputtering. Zirconium plating can survive heat loads without any visible damage or general cracking. Therefore, in the extreme environment, the zirconia coating interfaces are stable, which is in favor of the reinforcement of Wf/W composites [75, 76].
Summary and outlook
The thermal stability and mechanical properties of the HfC dispersion have strengthened W alloys as plasma-facing components in fusion devices. Recent advances in research and development of W-ZrC alloys for plasma-facing components in fusion devices. Effect of high-temperature pressing and annealing on the mechanical properties and thermal conductivity of W–Y2O3.
Development of ultra-fine-grained W wt% TiC and its superior resistance to neutron and 3 MeV He-ion radiation. Grain growth behavior and mechanical properties of zirconium microalloyed and nanosized zirconium carbide dispersion strengthened tungsten alloys. Effect of hot rolling on the microstructure and fracture behavior of a bulk fine-grained W-Y2O3 alloy.
Design of highly thermal shock resistant tungsten alloys with nanometer-scale K-type bubbles. In situ synchrotron tomography evaluation of the stiffening effect by semi-ductile fiber reinforcement in a tungsten fiber reinforced tungsten composite system. Improved toughness and stable crack propagation in a novel chemical vapor infiltration tungsten fiber reinforced tungsten composite.
Development of tungsten fiber-reinforced tungsten composites for use in potassium-doped DEMO-tungsten wire.