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In order to evaluate the magnetic surface current density distributions, the electron guiding center orbits were calculated with the equilibrium fitting plasma equilibrium analysis. The current density distributions in electron cyclotron-heated plasma were estimated from the orbit analyses in the equilibrium plasma shaping for the fundamental and the second-harmonic resonant electrons separately. The current density distribution profiles on the equatorial plane were obtained for the electrons with initially positive and negative velocities parallel to the magnetic field direction as well as the trapped electrons. The surface averaged current density profiles of the closed flux surfaces were also evaluated. A significant amount of the positive current density distributions appeared outside the last closed flux surface (LCFS), while all the negative current density distributions were evaluated inside the LCFS. The trapped electrons being the second-harmonic electron cyclotron resonant contributed the negative current inside the LCFS. The positive current density distributions outside the LCFS were significant for the driven current density for both the fundamental and second-harmonic resonances. [ABSTRACT FROM AUTHOR]

In the present RF-driven plasma with a lot of high-energy electrons, there may be anisotropic plasma pressure, which makes the usual equilibrium analysis difficult, but the Cauchy condition surface method can reconstruct the plasma shape precisely regardless of the anisotropy. In addition, the plasma current effect in the open magnetic surfaces outside of the closed magnetic surfaces is considered in the RF-driven divertor plasma. In the reconstruction process, singular value (SV) decomposition is used and optimal criterion function for generalized cross validation is estimated concerning truncation or reduction of the small-SV components. [ABSTRACT FROM PUBLISHER]

• A method for inserting a well defined fatigue precrack in W is established. • Continuous in-situ observations on crack formation and extension during fatigue precracking are performed. • Reliable fracture toughness values of ITER specification W (ALMT-grade) are assessed 4. The RT fracture toughness values are ~10MPa√m for the T-L and 12~13MPa√m for the L-T orientation. • Orientational variation in RT fracture toughness is comparably small in the ALTM-grade plate. Fracture toughness of the divertor armor in ITER needs to be elucidated for prediction of the response of armor materials to intense heat loading. The present study has been performed to establish a method for inserting a well, defined fatigue precrack into the test specimens and measure the reliable fracture toughness values of tungsten (W) materials that exhibit low temperature brittleness. Sub-sized, single edge notched bend (SENB) specimens with two orientations, L -T and T-L, taken from a commercially available pure W plate manufactured in accordance with the ITER material specifications (ITER specification W, ALMT-grade), were precracked in two-step fatigue loading: fully uniaxial compression fatigue to provoke a crack from the notch tip, and subsequent 3-point bend (3 PB) fatigue to extend the crack length for the minimization of influence of the residual tensile stresses generated by compression fatigue. During compression and 3 PB fatigue loading the fatigue crack was closely monitored by continuous in-situ observations on the notch tip. Continuous tracing of the crack tip position has enabled capture of the fatigue cracking behavior as a kinematic response in a rolled W material, disclosing a marked difference in crack inducement and extension between the two orientations. 3 PB fracture testing of the precracked specimens at room temperature (RT) yielded ~10 MPa√m for the T-L and 12~13 MPa√m for the L -T orientation as fracture toughness: anisotropic variation in fracture toughness of the W plate is comparatively small. Fracture surface observations reveal that a crack path is entirely transgranular for the L -T, while crack propagation involves intergranular fracture to a large extent for the T-L orientation. These results obtained are discussed and compared with the literature data. [ABSTRACT FROM AUTHOR]

Abstract Spark plasma sintering (SPS) is one of the methods used to achieve the low-temperature densification of refractory metal materials. In this study, powder prepared through a wet chemical method was consolidated via SPS at 1100 °C, 1200 °C, 1350 °C, 1600 °C, and 1800 °C to obtain a high-performance W-TiC-Y 2 O 3 composite material. Densification was studied by analyzing the densification curve and changes in the microstructure of the samples. This process could be divided into three stages: the bonding stage, the sintering neck growth stage, and the shrinkage and spherification stage of closed pores. Surface diffusion and grain boundary diffusion played different roles in densification. The density, grain size, and Vickers hardness of the tungsten material increased significantly as temperature increased. This study evaluated the sintering process and provided a basis for obtaining high-performance tungsten materials through SPS. Highlights • Surface diffusion and grain boundary diffusion played different roles in densification. • The density, grain size, and Vickers hardness of tungsten increased as temperature increased. • The densification of the composite accelerated at the initial stage of sintering but decelerated after a certain period. • The densification of the powder at different sintering stages was influenced by different mechanisms. [ABSTRACT FROM AUTHOR]

The transient thermal shock behaviors of W–ZrC/Sc 2 O 3 composites with different ZrC contents were evaluated using transient thermal shock test by electron and laser beams. The effects of different ZrC doping contents on the surface morphology and thermal shock resistance of W–ZrC/Sc 2 O 3 composites were then investigated. Similarity and difference between effects of electron and laser beam transient heat loading were also discussed in this study. Repeated heat loading resulted in thermal fatigue of the irradiated W–ZrC/Sc 2 O 3 samples by thermal stress, leading to the rough surface morphologies with cracks. After different transient thermal tests, significant surface roughening, cracks, surface melting, and droplet ejection occurred. W–2vol.%Sc 2 O 3 sample has superior thermal properties and greater resistance to surface modifications under transient thermal shock, and with the increasing ZrC content in W alloys, thermal shock resistance of W–Zr/Sc 2 O 3 sample tends to be unsatisfied. [ABSTRACT FROM AUTHOR]

Fatigue pre-cracking performance and fracture toughness in polycrystalline tungsten (W) and molybdenum (Mo) have been investigated in relation to grain boundary (GB) configuration with respect to the crack advance direction. Sub-sized, single edge notched bend (SENB) specimens with three different orientations, R-L (ASTM notation) for a forged Mo rod and L-S and T-S for a rolled W plate, were pre-cracked in two steps: fully uniaxial compression fatigue loading to provoke crack initiation and its stable growth from the notch root, and subsequent 3-point bend (3PB) fatigue loading to extend the crack. The latter step intends to minimize the influence of the residual tensile stresses generated during compression fatigue by moving the crack tip away from the plastic zone. It is shown that fatigue pre-cracking performance, especially pre-crack extension behavior, is significantly affected by the specimen orientation. The R-L orientation, giving the easiest cracking path, permitted crack extension completely beyond the plastic zone, while the L-S and T-S orientations with the thickness cracking direction of the rolled plate sustained the crack lengths around or possibly within the plastic zone size due to difficulty in crack advance through an aligned grain structure. Room temperature fracture toughness tests revealed that the 3PB fatigued specimens exhibited appreciably higher fracture toughness by about 30% for R-L, 40% for L-S and 60% for T-S than the specimens of each orientation pre-cracked by compression fatigue only. This indicates that 3PB fatigue provides the crack tip front out of the residual tensile stress zone by crack extension or leads to reduction in the residual stresses at the crack tip front. Strong dependence of fracture toughness on GB configuration was evident. The obtained fracture toughness values are compared with those in the literature and its strong GB configuration dependence is discussed in connection with the appearance of pop-in. [ABSTRACT FROM AUTHOR]

Pure tungsten and tungsten alloys with 1, 2, and 3 wt.% Lu 2 O 3 were fabricated by mechanical alloying and spark plasma sintering at 1600 °C for 3 min. These samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive spectroscopy, Vickers microhardness, thermal conductivity analyses, thermal shock test, and deuterium retention. Results revealed that the microhardnesses of the samples have a similar trend with the relative density. With increased the doped Lu 2 O 3 content, the relative density and microhardness increased and the Lu 2 O 3 particles significantly increased the density and strengthened of tungsten alloy. With increased temperature from 300–1100 K, the thermal conductivity decreased with increased Lu 2 O 3 content. The doped Lu 2 O 3 particles revealed good enhancement effect in the thermal shock resistance and a good influence in the deuterium retention. [ABSTRACT FROM AUTHOR]

The plasma control system (PCS) of QUEST was a centralized system, which lost its scalability because of the overload imposed on its central processing unit (CPU) of the PCS, making it impossible to add new functions. Thus, the PCS is distributed into a main workstation (WS) and subsystem (SS) with a reflective memory (RFM) in order to share data between these systems so as to mitigate the load on each system. As a result, 128 double-precision floating-point numbers (DBLs) can be transferred from the SS to the WS with a maximum latency of 250 μs. The WS and the SS each have quad-core CPUs, and tasks are executed in parallel. Although one of the four cores is intermittently occupied by up to 90% by this transaction, the occupation is normally 60%. A time correction procedure is used to map the recorded data sets on the WS and the SS to a common time base by referring to the time difference between two systems. [ABSTRACT FROM AUTHOR]

W-2%vol Y 2 O 3 composite material were prepared by wet-chemical and rolling methods. A comparative study was conducted with commercially pure tungsten. The laser thermal shock and the damage behavior of the material after helium ion irradiation were studied. The damage behavior was analyzed through X-ray diffractometry, field emission scanning electron microscopy, focused ion beam, field emission transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Results showed that W–Y 2 O 3 composite material have higher resistance to laser thermal shock than pure tungsten. Helium ion irradiation further illustrated that the cracking caused by laser thermal shock is dominated by intergranular cracks. In addition, tungsten matrix damage is associated with grain orientation deformation after the helium ion irradiation of pure tungsten and W–Y 2 O 3 composite material, and the grain orientation resistance to helium ion irradiation damage is higher than that to increasing grain boundary density. Several helium bubbles were found in the tungsten matrix, the fuzz structure, and the Y 2 O 3 particles, and all the helium bubbles were polyhedral rather than spherical. • W–Y 2 O 3 composite possess higher thermal shock resistance than pure tungsten. • Compared with increasing grain boundary density, grain orientation is more favorable to resist irradiation damage. • Helium bubbles were observed in the Y 2 O 3 particles. • The reported helium bubbles were polyhedral rather than spherical. [ABSTRACT FROM AUTHOR]

To study the D 2 retention behavior of W–ZrC/Sc 2 O 3 composites, mirror-polished samples prepared by spark plasma sintering (SPS) were exposed to different irradiation doses at room temperature (RT). TDS measurements were subsequently performed from RT to 900 K. Results revealed that Sc 2 O 3 particles did not benefit the D 2 + ion irradiation resistance, whereas W–1vol% ZrC/2 vol% Sc 2 O 3 composites showed superior irradiation resistance over other samples. D 2 implantation was also performed at 523 K with the irradiation dose of 1 × 1020 D 2 +/m2 to study the influence of temperature on D 2 retention during the capture process, which could apparently decrease D 2 retention by low-energy traps. Only small dislocation loops or precipitates were observed in W–1vol% ZrC/2 vol% Sc 2 O 3 sample after irradiation up to 1.0✕1021 D 2 +/m2. • The effect of ZrC/Sc 2 O 3 doping on irradiation resistance behavior of W materials was investigated. • 1 vol% ZrC/2 vol% Sc 2 O 3 composite possess better irradiation resistance than SPS/W. • Increasing implantation temperature decrease D 2 retention by low-energy traps. [ABSTRACT FROM AUTHOR]