716 research outputs found
Thermal and mechanical properties of W/Cu composite materials for ITER heat sink applications
One of the main challenges in the development of a fusion power plant is the adequate selection of
the materials that will withstand the extreme conditions of temperature, load and radiation. Among
those issues, the control of the heat removal by the divertor is critical, hence the highest heat load
inside the reactor will be found in it. For this purpose, one solution proposed is a novel optimized
water-cooled monoblock divertor consisting of W as plasma facing material and W/Cu composites as
the baseline heat sink material. The attraction of these metal matrix composites in fusion applications
is twofold: the W matrix provides the necessary strength of the composite at high temperatures,
while Cu provides the required high thermal conductivity for efficient heat removal in the cooling
system. In this context, the goal of this study is the characterization of W-Cu composite materials
produced by means of liquid Cu infiltration of open porous W preforms. In order to achieve it, a new
experimental device was set up to test the composites under high vacuum atmosphere while in the
temperature range between 273 K and 1073 K. Tensile and fracture tests in three point bending
configuration have been conducted in this temperature range and atmosphere. Additionally,
micromechanical and physical characterization was also performed by means of micro and
nanoindentation and High Temperature X-Ray Diffraction respectively
Role of remote interfacial phonons in the resistivity of graphene
The temperature () dependence of electrical resistivity in graphene
has been experimentally investigated between 10 and 400 K for samples prepared
on various substrates; HfO, SiO and h-BN. The resistivity of graphene
shows a linear -dependence at low and becomes superlinear above
a substrate-dependent transition temperature. The results are explained by
remote interfacial phonon scattering by surface optical phonons at the
substrates. The use of an appropriate substrate can lead to a significant
improvement in the charge transport of graphene
Controlled-NOT logic gate for phase qubits based on conditional spectroscopy
A controlled-NOT logic gate based on conditional spectroscopy has been
demonstrated recently for a pair of superconducting flux qubits [Plantenberg et
al., Nature 447, 836 (2007)]. Here we study the fidelity of this type of gate
applied to a phase qubit coupled to a resonator (or a pair of capacitively
coupled phase qubits). Our results show that an intrinsic fidelity of more than
99% is achievable in 45ns.Comment: 5 pages, 5 figures, To appear in Quantum Inf. Pro
First principle study of intrinsic defects in hexagonal tungsten carbide
The characteristics of intrinsic defects are important for the understanding
of self-diffusion processes, mechanical strength, brittleness, and plasticity
of tungsten carbide, which present in the divertor of fusion reactors. Here, we
use first-principles calculations to investigate the stability of point defects
and their complexes in WC. Our calculation results confirm that the formation
energies of carbon defects are much lower than that of tungsten defects. The
outward relaxations around vacancy are found. Both interstitial carbon and
interstitial tungsten atom prefer to occupy the carbon basal plane projection
of octahedral interstitial site. The results of isolated carbon defect
diffusion show that the carbon vacancy stay for a wide range of temperature
because of extremely high diffusion barriers, while carbon interstitial
migration is activated at lower temperatures for its considerable lower
activation energy. These results provide evidence for the presumption that the
800K stage is attributed by the annealing out of carbon vacancies by long-range
migration.Comment: Submitted to Journal of Nuclear Material
Melt infiltrated Tungsten-Copper composites as advanced heat sink materials for plasma facing components of future nuclear fusion devices
The exhaust of power and particles is regarded as a major challenge in view of the design of a magnetic confinement
nuclear fusion demonstration power plant (DEMO). In such a reactor, highly loaded plasma facing components
(PFCs), like the divertor vertical targets, have to withstand both severe high heat
ux loads and considerable neutron
irradiation. Existing divertor target designs make use of monolithic tungsten (W) and copper (Cu) material grades
that are combined in a PFC. Such an approach, however, bears engineering difficulties as W and Cu are materials
with inherently different thermomechanical properties and their optimum operating temperature windows do not overlap.
Against this background, W-Cu composite materials are promising candidates regarding the application to the
heat sink of highly loaded PFCs. The present contribution summarises recent results regarding the manufacturing
and characterisation progress of such W-Cu composite materials produced by means of liquid Cu melt infiltration of
open porous W preforms. On the one hand, this includes composites manufactured by infiltrating powder metallurgically
produced W skeletons. On the other hand, W-Cu composites based on textile technologically produced fibrous
reinforcement preforms are discussed
European DEMO divertor target: Operational requirements and material-design interface
Recently, an integrated program of conceptual design activities for the European DEMO reactor was launched in the framework of the EUROfusion Consortium, where reliable power handling capability was identified as one of the most critical scientific as well as technological challenges for a DEMO reactor. The divertor is the key in-vessel plasma-facing component being in charge of power exhaust and removal of impurity particles. The DEMO divertor target will have to withstand extreme thermal loads where the local peak heat flux is expected to reach up to 20 MW/m2 during slow transient events in DEMO. To assure sufficient heat removal capability of the divertor target against normal and transient operational scenarios under expected cumulative neutron dose of up to 13 dpa is one of the fundamental engineering challenges imposed on target design. To develop the design of the DEMO divertor and related technologies, an R&D work package 'Divertor' has been set up in this consortium. The subproject 'Target Development' is devoted to the development of the conceptual design and the core technologies of the plasma-facing target. Devising and implementing novel structural heat sink materials (e.g. W/Cu composites) to advanced target design concepts is one of the major objectives of this subproject. In this paper, the underlying design requirements imposed by the envisaged power exhaust goal and the prominent material-design interface issues are discussed. In addition, the candidate design concepts being currently considered are presented together with the related material issues. Finally, the first results achieved so far are presented
European divertor target concepts for DEMO: Design rationales and high heat flux performance
The divertor target plates are the most thermally loaded in-vessel components in a fusion reactor where high heat fluxes are produced on the plasma-facing components (PFCs) by intense plasma bombardment, radiation and nuclear heating. For reliable exhaust of huge thermal power, robust and durable divertor target PFCs with a sufficiently large heat removal capability and lifetime has to be developed. Since 2014 in the framework of the preconceptual design activities of the EUROfusion DEMO project, integrated R&D efforts have been made in the subproject ‘Target development’ of the work package ‘Divertor’ to develop divertor target PFCs for DEMO. Recently, the first R&D phase was concluded where six (partly novel) target PFC concepts were developed and evaluated by means of non-destructive inspections and high-heat-flux fatigue testing. In this paper, the major achievements of the first phase activities in this subproject are presented focusing on the design rationales of the target PFC concepts, technology options employed for small-scale mock-up fabrication and the results of the first round high-heat-flux qualification test campaign. It is reported that the mock-ups of three PFC concepts survived up to 500 loading cycles at 20 MW/m² (with hot water cooling at 130 °C) without any discernable indication of degradation in performance or structural integrity
The Vacuum System of HIRFL
AbstractThe vacuum system of Heavy Ion Research Facility in Lanzhou (HIRFL) is a large and complex system. HIRFL consists of two ECR ion sources, a sector focus cyclotron (SFC), a separate sector cyclotron (SSC) and a multi-purpose cooling storage ring system which has a main ring (CSRm) and an experiment ring (CSRe). Several beam lines connect these accelerators together and transfer various heavy ion beams to more than 10 experiment terminals. According to the requirements of the ion acceleration and ion lifetime, the working pressure in each accelerator is different. SFC is nearly 50 years old. After upgrade, the working pressure in SFC is improved from 10-6mbar to 10-8mbar. The pressure in SSC which was built in the 1980s reaches the same level. The cooling storage ring system with a length of 500m came into operation in 2007. The average pressures in CSRm and CSRe are 5×10-12mbar and 8×10-12mbar respectively. Different designs were adopt for vacuum system of a dozen beam lines to meet specific requirement of each experiment terminal. Along with the extensive development of the heavy ion researches and applications, new accelerators of HIRFL are under construction. The vacuum system of the new machines will be designed and constructed followed the overall schedule
Dealing Automatically with Exceptions by Introducing Specificity in ASP
Answer Set Programming (ASP), via normal logic programs, is known as a suitable framework for default reasoning since it offers both a valid formal model and operational systems. However, in front of a real world knowledge representation problem, it is not easy to represent information in this framework. That is why the present article proposed to deal with this issue by generating in an automatic way the suitable normal logic program from a compact representation of the information. This is done by using a method, based on specificity, that has been developed for default logic and which is adapted here to ASP both in theoretical and practical points of view
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