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Experimental results on a liquid metal magnetohydrodynamic (MHD) turbulent flow through a circular conductive pipe subject to a uniform transversal magnetic field are summarized in this paper. The results of the MHD turbulent velocity distributions inside the conductive pipe are obtained. The velocity profiles along the center line of the middle cross section of the pipe are given. There are no big velocity jets in the Robert layers. The velocity distribution agrees well with the numerical simulation result. The transient turbulent velocity of one point in above mentioned line changing with times are measured in the experiment, it is found that the transient velocity varies dramatically compared to the average velocity at high Reynolds number (Re). The strong magnetic field suppresses the turbulent velocity fluctuation. The velocity profiles varying with the different Reynolds numbers at the same Hartmann number (Ha) are also presented in this paper. It is shown that the velocity in the center fluid area decreases with the Reynolds numbers increasing. The Reynolds stresses at different Reynolds numbers and Hartmann numbers are also derived from experimental data. The Reynolds stresses decrease with the increasing of Hartmann numbers. The map of laminar-turbulent transition for MHD circular conductive pipe flows at high Reynolds and Hartmann numbers are also presented. A different fluid instability from the theoretical prediction in Refs. Lielausis (1975) and Moresco et al. (2004) is observed and the transition condition is Re/Ha > 20.

In this work, thermal ageing of the reduced activation ferritic/martensitic steel CLF-1 with a nitrogen content of 0.025% has been performed at temperatures of 823 K and 873 K for 6000 h. Mechanical properties (hardness, tensile and Charpy impact) and microstructure characterisation has been carried out. After thermal ageing treatments, the steels showed similar values of hardness and tensile properties and a slight deterioration of impact properties were observed. After long term thermal ageing, the M23C6-type precipitation coarsens and agglomerates along lath and grain boundaries. Compared with steels that have lower nitrogen content, the coarsening and agglomeration of M23C6 in the steels with higher nitrogen content is much lower and the steel shows higher microstructural stability. (C) 2013 Elsevier B. V. All rights reserved.

Beryllium and tungsten have been selected as the plasma facing materials of the ITER first wall (FW) and divertor chamber, respectively. China, as a participant in ITER, will share the manufacturing tasks of ITER first-wall mockups with the European Union and Russia. Therefore ITER-grade beryllium has been developed in China and a kind of vacuum hot-pressed (VHP) beryllium, CN-G01, was characterized for both physical, and thermo-mechanical properties and high heat flux performance, which indicated an equivalent performance to U.S. grade S-65C beryllium, a reference grade beryllium of ITER. Consequently CN-G01 beryllium has been accepted as the armor material of ITER-FW blankets. In addition, a modification of tungsten by TiC dispersion strengthening was investigated and a W–TiC alloy with TiC content of 0.1 wt.% has been developed. Both surface hardness and recrystallization measurements indicate its re-crystallization temperature approximately at 1773 K. Deuterium retention and thermal desorption behaviors of pure tungsten and the TiC alloy were also measured by deuterium ion irradiation of 1.7 keV energy to the fluence of 0.5–5 × 10 18 D/cm 2 ; a main desorption peak at around 573 K was found and no significant difference was observed between pure tungsten and the tungsten alloy. Further characterization of the tungsten alloy is in progress.

Effect of contact resistance on magnetohydrodynamic (MHD) laminar flows through circular pipes are investigated by numerical simulations. A numerical method is proposed to investigate this issue. This method is that the induced magnetic field is individually calculated through two different governing equations in the liquid and the solid domains, special boundary conditions are given considering effects of the contact resistance. This method is validated by comparing with analytical solution and another numerical method. Numerical results of the velocity distribution and the MHD pressure drop affected by the contact resistance through circular pipes are given. It is shown that the contact resistance has a significant impact on the MHD pressure drop under the conditions of the fusion liquid metal blanket , and normally, the big contact resistance as a result of poor wetting can cause the MHD pressure drop to be several times lower than no contact resistance case. In addition, non-uniform contact resistance will cause the jet instability in the Robert layer and form a larger jet near the area of contact resistance. In the end, numerical results are compared with experimental results which include the effect of non-uniform contact resistance on the velocity distribution; it is indicated that numerical results are in good agreement with experimental results and validates that the larger velocity jet will be caused by the non-uniform contact resistance from experimental results.

Tungsten was coated on a W/Cu functionally graded material (FGM) by chemical vapor deposition technique (CVD), and then the tungsten coated tile was brazed on the CuCrZr heat sink with a cooling channel. The thickness of CVD-W was 2 mm deposited by a fast rate of about 0.7 mm/h. The features of the CVD-W coating including morphology, element composition and thermal properties were characterized. A tungsten coating with high density, purity and thermal conductivity is achieved. The bonding strength between the CVD-W layer and FGM was measured using bonding tensile tests. Thermal screening and fatigue tests were performed on the CVD-W mock-ups under fusion relevant conditions using an electron beam device. Experimental results showed that the CVD-W mock-up failed by melting of Cu beneath the tungsten layer under a high heat load of 14.5 MW/m2 and 30 s pulse duration. Thermal fatigue tests showed that the CVD-W mock-up could sustain 1000 cycles at a heat load of 11.7 MW/m2 absorbed power density and 15 s pulse duration without visible failure.

Magnetohydrodynamics (MHD) laminar flows through circular pipes are studied in this paper by numerical simulation under the conditions of Hartmann numbers from 18 to 10000. The code is developed based on a fully developed modeling and validated by Samad's analytical solution and Chang's asymptotic results. After the code validation, numerical simulation is extended to high Hartmann number for MHD circular pipe flows with conducting walls, and numerical results such as velocity distribution and MHD pressure gradient are obtained. Typical M-type velocity is observed but there is not such a big velocity jet as that of MHD rectangular duct flows even under the conditions of high Hartmann numbers and big wall conductance ratio. The over speed region in Robert layers becomes smaller when Hartmann numbers increase. When Hartmann number is fixed and wall conductance ratios change, the dimensionless velocity is through one point which is in agreement with Samad's results, the locus of maximum value of velocity jet is same and effects of wall conductance ratio only on the maximum value of velocity jet. In case of Robert walls are treated as insulating and Hartmann walls as conducting for circular pipe MHD flows, there is big velocity jet like as MHD rectangular duct flows of Hunt's case 2.

The duct with a flow channel insert (FCI) which is made of silicon carbon composite (SiC f /SiC) is a key element in dual coolant lead lithium (DCLL) blanket, and the most important problems of FCI is the magnetohydrodynamics (MHD) issues. In this paper it is presented the study of MHD issues in FCI duct flow using Fluent code, the modification of the FCI with a pressure equalization slot (PES) has been considered in this simulation. Numerical and experimental results of velocity distribution and MHD pressure drop of FCI were given in this paper, then compare and discuss the difference between them. From the experimental and numerical results it indicated that the FCI with insulating material could greatly reduce MHD pressure drop. For fully developed MHD duct flow a general second-order simple method has been developed which solve the unsteady equations and let the steady state be approached asymptotically at large times. Using this method can get accurate result for MHD duct flow in the condition of high Hartmann number without FCI. Then using this method numerical simulation was performed with MHD duct flow with FCI.

Vacuum plasma sprayed tungsten coating on graphite and copper substrates has been prepared. VPS-W coated graphite has multilayered silicon and tungsten interface pre-deposited by physical vapor deposition (PVD) and VPS-W coated copper has graded transition interlayer. VPS-W coating was characterized, and then the high heat flux properties of the coating were examined. Experimental results indicated that both VPS-W coated graphite and VPS-W coated copper could endure 1000 cycles without visible failure under a heat flux of approximately 5 MW/m 2 absorbed power density and 5 s pulse duration. A comparison between the present VPS-W coated graphite and VPS-W coated carbon fiber composite (CX-2002U) with Re interface made by Plansee Aktiengesllshaft was carried out. Results show that both Re and Si are suitable as intermediate layer for tungsten coating on carbon substrates.

MHD phenomena in a duct flow were studied experimentally by using copper electrodes inserted into the wall of a perfectly insulated duct. The electrodes were connected using a copper wire to imitate different insulator coating imperfection conditions. The experimental results show instabilities of electric potential at the wall (surface instabilities) as well as instabilities in the pressure and velocity (bulk instabilities). The instabilities are strongly dependent on the scale of the copper wire. Three different cases were studied (at the same flow regimes, but with different electrode connections), where the potential at the duct wall is smaller, equal to or higher than the product of duct diameter 2a0 and transverse magnetic field B0 and average velocity V0. MHD pressure drop ΔP also exhibits significant changes.

Liquid metal free surface flows (films, jets and droplets) are considered as prospective coolants in diverter/limiter system and first wall in fusion reactor, but the knowledge of liquid metal free surface, particularly jet flows, is very limited. In this article, the stability of a jet flow under a gradient magnetic field is investigated, and its MHD effects are the top concern. Firstly, a simplified model is developed to analyze the MHD effects of the jet flow and to explain the reason why it can keep stable, and the examination of the induced electric potential and currents of the jet flow is also included. Secondly, numerical simulation based on the approach of solving the electric potential equation was proceeded to support the theoretical analysis. Finally, experiments with different value of B0 (maximum value of the magnetic field) and v 0 (average fluid velocity at the nozzle exit), and different kind of nozzle were performed on the Liquid Metal Experimental Loop (LMEL) in Southwestern Institute of Physics (SWIP), and there's a good agreement with experimental data and theoretical results. Qualitatively, a jet flow under a gradient magnetic field can keep its shape stable due to electromagnetic (EM) force in its direction and the compressed EM force in its cross-section, meanwhile, the reduction in velocity leads to a shorter range distance and a lager radius of cross-section of the jet flow. These effects are closely related to the parameters of the radius of the nozzle, the values of B0 and v 0 .

Tungsten divertor plates in fusion reactors will be subject to helium bombardment. Helium retention and thermal desorption is a concerned issue in controlling helium ash. In the present study, fluence dependence of thermal desorption behavior of helium in tungsten was studied at different irradiation temperatures and ion energies. Results showed that helium desorption could start at ∼400 K with increasing fluence, while no noticeable peaks were detected at low fluence. Total helium desorption reached a saturation value at high fluence range, which was not sensitive to irradiation temperature or ion energy for the conditions evaluated. Surface modifications caused by either ion irradiation or thermal desorption were observed by SEM. The relationship of surface modifications and helium desorption behavior was discussed. Some special features of elevated irradiation temperature and lower ion energy were also indicated.

The hydrogen embrittlement behavior of a V4Cr4Ti alloy (NIFS-Heat 2) has been studied using tensile tests, impact tests and J integral tests. Hydrogen in the alloy was high up to 310 wppm by exposures in a hydrogen atmosphere. The alloy showed different sensitivities to the hydrogen embrittlement in the tests. Hydrogen-induced solid solution hardening occured but caused slight loss in the ductility of the alloy before 215 wppm H in the tensile test. However, the impact toughness, J 1c and the tearing modulus ( T mat ) decreased largely with increasing hydrogen concentration, indicated that the critical hydrogen concentration required to embrittle the alloy might be lower than 130 wppm. The fracture characteristics varied a lot for the different specimens. All these differences were thought being resulted from the stress concentration and the stress assisted hydrogen diffusion in the compact tension specimen and in the necking area of a tensile specimen.

A pulsed electron beam test was used to simulate the thermal response of plasma facing materials under high heat loads during plasma disruptions, particularly for relatively 'long' duration off-normal events such as plasma vertical displacement events. The erosion and erosion products of purified tungsten made by powder metallurgy (PM-W), W and B 4 C plasma sprayed coatings on CFC or copper and C/C composite were investigated. The time evolution of the target current indicates that the erosion products or screening clouds partly or completely shield the incident electron beam, leading to a reduction of the target current and changes in the target current profile. The weight loss of PM-W is smaller than that of the tungsten coating or C/C composite, which is in agreement with the erosion behavior. Erosion products indicate that evaporation is a major erosion mechanism of PM-W, and exfoliation and particle emission are the dominant erosion mechanisms of carbon-based materials and W plasma sprayed coatings.

Experiments were performed using copper electrodes inserted into the wall of a perfectly insulated duct to simulate insulator coating flaking or cracking. The results show that surface electric potential U and MHD pressure drop Δ P exhibit a non-monotonic behavior with increasing V 0 , while the magnetic field B 0 is held constant. Additional experiments were also performed keeping all external experimental conditions fixed while measuring the change of U , V 0 , B 0 , and Δ P with increasing time. It was found that while all external experimental conditions were kept constant, the system changed by itself and U , V 0 and Δ P exhibited a non-monotonic behavior with increasing time. The results seem contrary to the law of Δ P ∝ V 0 B 0 n , but are consistent with conservation of energy, which implies that the change is due to some inherent feature of the system, or possibly instabilities, which may occur due to insulator coating imperfections.

Several V–Cr–Ti–Al–Si alloys were studied with respect to their mechanical performances after exposure to hydrogen environments. The alloys were developed in China by using a melting process in a magnetic floating furnace. Most of the alloys had a high oxygen concentration from 700 to 1100 wppm since the forging and hot rolling were performed in air at elevated temperature. The results showed a synergistic effect of oxygen and hydrogen. The ductility loss correlated largely with the hydrogen concentration up to 113 wppm. Both V4Ti and V4TiSi showed a relatively higher resistance to hydrogen embrittlement in comparison with other alloys such as V4Cr4Ti and V4Ti3Al.

Plasma irradiation experiments of several kinds of carbon materials and molybdenum were performed in the HL-1M tokamak. The samples emerged into plasma by a depth of 1.5 cm with an angle of 45° between sample surface and magnetic field. After ≈300 plasma discharges with ohmic and NBI heating, melting, microstructure of thin flakes, gas holes and bubbles were found on the surface of molybdenum. No obvious damages were found on the surface of carbon materials, only carbon fibers of 3D-C/C composite were preferentially eroded. Weight changes indicated that most of the samples had little weight loss but few of the samples had large weight increments in which some droplet-shape deposits were found on their surface. Most of the erosion and re-depositions occurred at random on the surface of samples implied that the dominant factor influenced the erosion and re-deposition of plasma facing materials was tokamak plasma disruption.

Several V–Cr–Ti–Al–Si alloys were studied or reviewed of their mechanical properties after their exposure to oxygen, hydrogen and neutron irradiation environments. The results showed that the oxidation kinetic of V4Cr4Ti alloy exhibited parabolic behavior in a flowing argon gas with low partial pressure oxygen over the temperatures from 450 to 600 °C. Most of the alloys showed ductility losses with the increasing oxygen concentration with an exception of V4Ti3Al. Strong sensitivity to hydrogen embrittlement was found for the alloys with the combination of high oxygen concentration and high mechanical strength. It was found that the effect of hydrogen and neutron irradiation on the uniform deformation capability caused by their hardening are equivalent with that of the strain hardening. Fine grain was recommended for the alloys to improve their properties against hydrogen embrittlement and neutron irradiation induced ductility loss.

Standard and Ti- and Nb-modified 316 SS specimens were irradiated with electrons in a high voltage electron microscope (HVEM) up to a dose of 40 dpa at 823 K. Void growth and carbide precipitate processes during irradiation were observed in situ and photographed. The experiment showed that 0.53% Ti-modified 316 SS had good resistance to void swelling, which is due to the small void size and low growth rate. The cold work did not increase the void swelling. In contrast, 0.49% and 0.78% Nb-modified 316 SS showed much higher void swelling than the others studied. However, the cold working of Nb-modified steels suppressed void swelling.