Showing papers in "Physica Scripta in 2007"
TL;DR: Work is in progress to completely replace, in 2008/9, the existing JET CFC tiles with a configuration of plasma facing materials consistent with the ITER design.
Abstract: Work is in progress to completely replace, in 2008/9, the existing JET CFC tiles with a configuration of plasma facing materials consistent with the ITER design. The ITER-like wall (ILW) will be cr ...
191 citations
TL;DR: In this paper, nano-sized Al2O3 particles having large specific surface area were added into sulfur electrode to prevent the dissolution of lithium polysulfides into liquid electrolyte and to promote the lithium/sulfur redox reaction.
Abstract: To prevent the dissolution of lithium polysulfides into liquid electrolyte and to promote the lithium/sulfur redox reaction, nano-sized Al2O3 particles having large specific surface area were added into sulfur electrode. The effects of nano-sized Al2O3 particles on the electrochemical properties of sulfur electrode for lithium/sulfur battery were investigated using CV measurements, charge/discharge tests and ionic conductivity measurements of liquid electrolyte. From the results, the sulfur electrode containing nano Al2O3 particles showed good cycle performance and higher discharge capacity of 660 mAh g−1-sulfur than that of the sulfur electrode without nano Al2O3. It is therefore concluded that the addition of nano-sized Al2O3 particles gives the beneficial effects of preventing the dissolution of lithium polysulfides into liquid electrolyte.
187 citations
TL;DR: In this paper, the homotopy perturbation method is used for solving an inverse parabolic equation and computing an unknown time-dependent parameter, which is an analytical procedure for finding the solutions of differential equations which is based on the constructing of a homhotopy with an imbedding parameter p[0,1] that is considered as an expanding parameter.
Abstract: Inverse problems of parabolic type arise from many fields of physics and play a very important role in various branches of science and engineering. In the last few years, considerable efforts have been expended in formulating accurate and efficient methods to solve these equations. In this research, the homotopy perturbation method is used for solving an inverse parabolic equation and computing an unknown time-dependent parameter. The homotopy perturbation technique is an analytical procedure for finding the solutions of differential equations which is based on the constructing of a homotopy with an imbedding parameter p[0,1] that is considered as an 'expanding parameter'. In this paper, a very brief introduction to the applications of the used technique and its new development is given. The results of applying this procedure to the studied parabolic inverse problem show the high accuracy, simplicity and efficiency of the approach.
134 citations
TL;DR: In this article, the authors measured deuterium depth profiles up to depths of 7-14 μm to understand the mechanism responsible for hydrogen isotope trapping in carbon fiber composites and tungsten both irradiated with D ions and exposed to D plasmas.
Abstract: Recent data on deuterium retention in carbon fibre composites and tungsten both irradiated with D ions and exposed to D plasmas are presented. Deuterium depth profiles measured up to depths of 7–14 μm allow understanding of the mechanism which is responsible for the hydrogen isotope trapping in these materials. In the CFC materials the amount of retained deuterium increases with the ion fluence at all irradiation temperatures in the range from 323 to 723 K. No saturation is reached as observed in pyrolytic graphite. Depth profiles show that saturation occurs only within a near surface layer corresponding to the ion range. The increase in total retention at near-room temperature is accompanied by an increasing of the long profile tail extending beyond 14 μm with the D concentration of about 10−1 at.% at a depth of 10 μm for fluences above 1024 D m−2. The depth at which deuterium is retained in tungsten (W) can be divided into three zones: (i) the near-surface layer (up to a depth of 0.2–0.5 μm depending on ion energy), (ii) the sub-surface layer (from ~0.5 to ~2 μm), and (iii) the bulk (>5 μm). Low-energy D ion irradiation modifies the W structure to depths of up to about 5 μm, both for W single crystals and polycrystalline W. The high D concentration (0.1–0.3 at.%) at depths of 1–3 μm relates to accumulation of D2 molecules in vacancy clusters and voids. These defects are supposed to be generated due to plastic deformation of the W surface caused by deuterium supersaturation within the near-surface layer.
128 citations
TL;DR: In this article, transient loads during ELMs and disruptions in present divertor tokamaks are described and used to carry out a extrapolation to ITER reference conditions and to draw consequences for its operation.
Abstract: New experimental results on transient loads during ELMs and disruptions in present divertor tokamaks are described and used to carry out a extrapolation to ITER reference conditions and to draw consequences for its operation. In particular, the achievement of low energy/convective type I edge localized modes (ELMs) in ITER-like plasma conditions seems the only way to obtain transient loads which may be compatible with an acceptable erosion lifetime of plasma facing components (PFCs) in ITER. Power loads during disruptions, on the contrary, seem to lead in most cases to an acceptable divertor lifetime because of the relatively small plasma thermal energy remaining at the thermal quench and the large broadening of the power flux footprint during this phase. These conclusions are reinforced by calculations of the expected erosion lifetime, under these load conditions, which take into account a realistic temporal dependence of the power fluxes on PFCs during ELMs and disruptions.
127 citations
TL;DR: In this article, the homotopy perturbation method is employed to solve a diffusion equation with source control parameters, which can take full advantage of the traditional perturbations method and homotonic technique.
Abstract: In this work, the solution of an inverse problem concerning a diffusion equation with source control parameters is presented. The homotopy perturbation method is employed to solve this equation. This method changes a difficult problem into a simple problem which can be easily solved. In this procedure, according to the homotopy technique, a homotopy with an embedding parameter p[0,1] is constructed, and this parameter is considered a 'small parameter', so the method is called the homotopy perturbation method, which can take full advantage of the traditional perturbation method and homotopy technique. The approximations obtained by the proposed method are uniformly valid not only for small parameters, but also for very large parameters. The fact that this technique, in contrast to the traditional perturbation methods, does not require a small parameter in the system, leads to wide applications in nonlinear equations.
118 citations
TL;DR: In this paper, the variational iteration method is applied to the 8-order initial-boundary value problems, and only one iteration is needed, and the obtained solutions are of remarkable accuracy.
Abstract: The variational iteration method is applied to the eighth-order initial-boundary value problems. Only one iteration is needed, and the obtained solutions are of remarkable accuracy.
102 citations
TL;DR: In this paper, the energy eigenvalues and corresponding eigenfunctions are calculated for the Kratzer potential, and the ladder operators for the one-dimensional (1D) and 3-dimensional krithm potential are obtained.
Abstract: In this paper, the energy eigenvalues and the corresponding eigenfunctions are calculated for the Kratzer potential. Then we obtain the ladder operators for the one-dimensional (1D) and 3D Kratzer potential. Finally, we show that these operators satisfy the SU(2) commutation relation.
98 citations
TL;DR: In this paper, the bound state solutions of the s-wave radial Schrodinger equation with Manning-Rosen potential were presented exactly by the standard method, and it was found that the solutions can be expressed by the generalized hypergeometric functions 2F1(a, b, c, z).
Abstract: The bound state solutions of the s-wave radial Schrodinger equation with Manning–Rosen potential are presented exactly by the standard method. It is found that the solutions can be expressed by the generalized hypergeometric functions 2F1(a, b; c; z). The intractable normalized wavefunctions are derived. We also study the special case for α=0 and find that this potential will reduce to the Hulthen potential.
95 citations
TL;DR: In this paper, the radial Schrodinger equation for the Hulthen potential was solved using the asymptotic iteration method (AIM) without using any approximations required by other methods.
Abstract: We present very accurate values for the bound state energy eigenvalues by solving the radial Schrodinger equation for the Hulthen potential within the framework of the asymptotic iteration method (AIM) for any ‘ states and for different screening parameters without using any approximations required by other methods. The AIM results are compared with the results of the numerical integration, the generalized pseudospectral, the supersymmetry, the variational and the shifted 1/N expansion methods and they are in very good agreement for different screening parameter, , values.
89 citations
TL;DR: In this article, a wavepacket approach was used to analyze the Jaynes-Cummings model with and without the rotating wave approximation (RWA) in a non-standard way.
Abstract: By using a wavepacket approach, this paper reviews the Jaynes–Cummings model with and without the rotating wave approximation (RWA) in a non-standard way. This gives new insight, not only of the two models themselves, but of the RWA as well. Expressing the models by field quadrature operators, instead of the typically used boson ladder operators, wavepacket simulations are presented. Several known phenomena of these systems, such as collapse-revivals, Rabi oscillation, squeezing and entanglement, are reviewed and explained in this new picture, either in an adiabatic or diabatic frame. The harmonic shape of the potential curves that the wavepackets evolve on and the existence of a level crossing make these results interesting in a broader sense not only for models in quantum optics, but especially in atomic and molecular physics.
TL;DR: In this article, four kinds of tungsten samples were exposed to 76 eV D-2(+) ions (38 eVD-1) at a flux of 10(22) D m(-2) s(-1).
Abstract: Four kinds of tungsten samples were exposed to 76 eV D-2(+) ions (38 eV D-1) at a flux of 10(22) D m(-2) s(-1). For plasma exposure at 315 K, blistering occurred more significantly on the unrecrystallized and single crystal W samples than the partially and fully recrystallized W samples. The un-recrystallized W sample showed the largest retention ratio at the same fluence. For samples exposed to higher fluences (up to 10(27) D m(-2)), the phenomena of bursting release of deuterium and blister bursting were clearly observed. Preliminary positron annihilation measurements indicated that the vacancy concentration in the near-surface region of tungsten increased after the deuterium plasma exposure. The results of electron back-scattering diffraction showed a strong dependence of blistering upon grain orientation, suggesting the possibility of alleviating blistering by selective texturing of tungsten for future fusion reactors.
TL;DR: In this paper, the analytical solutions of the fractional diffusion equations by an Adomian decomposition method are presented in the closed form and then their numerical solutions have been represented graphically.
Abstract: The time-fractional diffusion-wave equation is considered. The time-fractional diffusion equation is obtained from the standard diffusion equation by replacing the first-order time derivative with a fractional derivative of order α (0,2]. The fractional derivative is described in the Caputo sense. This paper presents the analytical solutions of the fractional diffusion equations by an Adomian decomposition method. By using initial conditions, the explicit solutions of the equations have been presented in the closed form and then their numerical solutions have been represented graphically. Four examples are presented to show the application of the present technique. The present method performs extremely well in terms of efficiency and simplicity.
TL;DR: In this article, a new exactly solvable potential which consists of the modified Kratzer potential plus a new ring-shaped potential βctg2θ/r2 was proposed, which is based on the Nikiforov-Uvarov method.
Abstract: We propose a new exactly solvable potential which consists of the modified Kratzer potential plus a new ring-shaped potential βctg2θ/r2. The exact solutions of the bound states of the Schrodinger equation for this potential are presented analytically by using the Nikiforov–Uvarov method, which is based on solving the second-order linear differential equation by reducing to a generalized equation of hypergeometric type. The wavefunctions of the radial and angular parts are taken on the form of the generalized Laguerre polynomials and the total energy of the system is different from the modified Kratzer potential because of the contribution of the angular part.
TL;DR: In this paper, the Darboux transformation method is successfully applied to two coupled nonlinear Schrodinger systems and the bright vector one-and two-soliton solutions including one-peak and two-peak solitons are further constructed via the iterative algorithm of Darbouque transformation.
Abstract: In nonlinear optical fibers, the vector solitons can be governed by the systems of coupled nonlinear Schrodinger from polarized optical waves in an isotropic medium. Based on the Ablowitz–Kaup–Newell–Segur technology, the Darboux transformation method is successfully applied to two coupled nonlinear Schrodinger systems. With the help of symbolic computation, the bright vector one- and two-soliton solutions including one-peak and two-peak solitons are further constructed via the iterative algorithm of Darboux transformation. Through the figures for several sample solutions, the stable propagation and elastic collisions for these kinds of bright vector solitons are discussed and the possible applications are pointed out in optical communications and relevant optical experiments.In addition, the conserved quantities of such two systems, i.e., the energy, momentum and Hamiltonian, are also presented.
TL;DR: In this article, an approximate solution of the Klein-Gordon equation for the general Hulthen-type potentials in D-dimensions within the framework of an approximation to the centrifugal term is obtained.
Abstract: An approximate solution of the Klein–Gordon equation for the general Hulthen-type potentials in D-dimensions within the framework of an approximation to the centrifugal term is obtained. The bound state energy eigenvalues and the normalized eigenfunctions are obtained in terms of hypergeometric polynomials.
TL;DR: In this article, binary and ternary tungsten-based alloys were synthesized by magnetron sputtering and the oxidation behavior was measured with a thermo balance set-up under synthetic air at temperatures up to 1273 K. Binary alloys of W-Si showed good self passivation properties by forming an SiO2 film at the surface.
Abstract: Self passivating tungsten-based alloys may provide a major safety advantage in comparison with pure tungsten (W) which is presently the main candidate material for the plasma-facing protection of future fusion power reactors. Films of binary and ternary tungsten alloys were synthesized by magnetron sputtering. The oxidation behaviour was measured with a thermo balance set-up under synthetic air at temperatures up to 1273 K. Binary alloys of W–Si showed good self passivation properties by forming an SiO2 film at the surface. Using ternary alloys the oxidation behaviour could be further improved. A compound of W–Si–Cr showed a reduction of the oxidation rate by a factor of 104 at 1273 K.
TL;DR: In this article, a marker structure consisting of a 7.5 μm Be film on top of a 2.5 µm Ni interlayer was developed and characterized by means of material analysis methods.
Abstract: Preparatory study for the operation of the JET tokamak with a full metal wall (ITER-like wall project) also comprises several activities aiming at the development of thin beryllium coatings. The purpose is 2-fold: (i) to coat Inconel® tiles of the inner wall cladding; (ii) to develop methods for production of films for so-called marker tiles in order to enable monitoring of Be erosion from limiters. Properties of the marker film must match, as closely as possible, those of bulk Be. The first step in the R&D process was to assess coating methods and the quality of layers deposited on test coupons. Smooth, dense Be films of high purity and good adhesion to the substrate were deposited with an average deposition rate of 5±0.5 nm s−1 to a thickness of 7.5 μm. A marker structure consisting of a 7.5 μm Be film on top of a 2.5 μm Ni interlayer deposited on a bulk Be block has been developed and characterized by means of material analysis methods. An overview of manufacturing processes and properties of the marker coatings is presented.
TL;DR: Combined magnetron sputtering and ion implantation (CMSII) is a deposition technique involving simultaneous magnetron and high energy ion bombardment of the coating during its growth as discussed by the authors.
Abstract: Combined magnetron sputtering and ion implantation (CMSII) is a deposition technique involving simultaneous magnetron sputtering and high energy ion bombardment of the coating during its growth. A high voltage pulse discharge (U=40 kV, τ=20 μs, f=25 Hz) is superposed over the magnetron deposition and in this way, positive ions are accelerated to the components to be coated, bombarding initially the substrate and then the coating itself. In the framework of the ITER-like wall project this method was applied to produce nanostructured W coatings on the carbon fibre composite (CFC) substrate. These coatings have been characterized in terms of adhesion, thickness, structure and resistance to high thermal loads (up to 23.5 MW m−2). Based on the results of these tests, which are presented in this paper, CMSII technology was selected for coating about 1100 tiles with a 10 μm tungsten layer for the JET first wall and divertor.
TL;DR: In this article, the bound state solutions of the Schr?dinger equation for an exponential-type potential with the centrifugal term are presented approximately, and it is shown that the complicated normalization wavefunctions can be expressed by the generalized hypergeometric functions?2F1(a, b; c; z).
Abstract: The bound-state solutions of the Schr?dinger equation for an exponential-type potential with the centrifugal term are presented approximately. It is shown that the complicated normalization wavefunctions can be expressed by the generalized hypergeometric functions?2F1(a, b; c; z). To show the accuracy of our results, we calculate the energy eigenvalues numerically for arbitrary quantum numbers n and l with two different values of the parameter ?. It is found that the results are in good agreement with those obtained by another method for short-range potential. Two special cases for s-wave case (l=0) and ?=1 are also studied briefly.
TL;DR: In this article, the phase formation of NiTi alloys via solid-state diffusion reactions is investigated, which can be explained in terms of Ni/Ti inter-diffusion processes.
Abstract: Phase formation of NiTi alloys via solid-state diffusion reactions is investigated. Samples of different Ni–Ti compositions were synthesized from elemental powders. The study revealed that the sintered samples consisted of Ti(Ni), NiTi2, NiTi and Ni3Ti in co-existence. Such co-existence is not expected from the equilibrium phase diagram, but can be explained in terms of Ni/Ti inter-diffusion processes. Thermodynamic analysis indicates that formation of NiTi is not favoured in primary reactions between Ni and Ti, but can be formed via secondary reactions involving primary reaction products of NiTi2 and Ni3Ti. Such reactions are difficult in solid state due to the difficulties of long-distance diffusion required. The synthesized alloys were found to exhibit much reduced martensitic transformation intensity, implying low transformation volume.
TL;DR: In this article, the authors compared all the data from different materials and sources, finding a distinctive relationship between the BDT temperature (TBDT) and the activation energy for BDT (EBDT), which holds over a wide range of materials, temperatures and activation energy values.
Abstract: The strain rate dependence of the brittle-to-ductile transition (BDT) temperature gives the activation energy controlling the BDT. Until recently, data were only available for a limited number of materials. Experimental data on the BDT of tungsten and other bcc metals have recently become available. We have compared all the data from different materials and sources, finding a distinctive relationship between the BDT temperature (TBDT) and the activation energy for BDT (EBDT) which holds over a wide range of materials, temperatures and activation energy values. The ratio EBDT/kTBDT gives approximately the value 25 for all the materials considered.
TL;DR: In this paper, the first H2 plasma was achieved with stainless steel as the plasma-facing material (PFM) in the Experimental Advanced Superconducting Tokamak (EAST) with doped graphite and W coatings.
Abstract: By the end of September 2006, the engineering commissioning of the Experimental Advanced Superconducting Tokamak (EAST) was completed and the first H2 plasma was achieved with stainless steel as the plasma-facing material (PFM). In the following phases, with gradual increase in the heating power, the EAST divertor targets have to handle expected heat loads up to ~10 MW m−2. The PFMs to be employed include doped graphite and W coatings. The former will be used to cover the whole plasma-facing surface in the first phase, and then the latter applied to replace the graphite tiles gradually in the second phase, and finally a whole W plasma-facing surface will be expected. Graphite has been studied for many years and contributed greatly to the HT-7 to achieve long pulses of some 100 s. The W coatings are being developed and the latest R&D development is reported in the paper.
TL;DR: In this paper, the one-dimensional thermal properties of the Kemmer oscillator have been investigated and compared with those of the Dirac oscillator with respect to its spectrum of energy.
Abstract: The one-dimensional thermal properties of the Kemmer oscillator have been investigated. Firstly, we have found the spectrum of energy of the oscillator in question, and then we have calculated its thermal properties. A comparison of our results with those of the Dirac oscillator has been made.
TL;DR: In this article, the Hirota method has been used to solve the (2+1)-dimensional nonlinear Schrodinger (CNLS) equations in nonlinear optical fibres.
Abstract: In nonlinear optical fibres, the evolution of two polarization envelopes is governed by a system of coupled nonlinear Schrodinger (CNLS) equations. In this paper, with the aid of symbolic computation, the analytical bright one- and two-soliton solutions of the (2+1)-dimensional CNLS equations under certain constraints are presented by employing the Hirota method. We have discussed the head-on and overtaking interactions which include elastic and inelastic collisions between two parallel bright solitons. In the interaction process, the intensities of solitons can exhibit various redistributions. We also point out that these properties have important physical applications in constructing various logic gates and nonlinear optical fibers.
TL;DR: In this paper, the authors provide an overview of processes and underlying physics governing tungsten melt erosion in the fusion plasma environment, including the formation of the melt layer and its motion in the magnetic field.
Abstract: The paper provides an overview of processes and underlying physics governing tungsten melt erosion in the fusion plasma environment. Experiments with three different bulk tungsten test-limiters were performed in TEXTOR: (i) thermally insulated solid plate fixed on a graphite roof-like limiter heated up by the plasma to the melting point, (ii) macro-brush of the ITER-relevant castellated structure and (iii) lamellae structure developed for the JET divertor. The main objectives were to determine the metal surface damage, the formation of the melt layer and its motion in the magnetic field. PHEMOBRID-3D and MEMOS-1.5D numerical codes were used to simulate the experiment with the roof-like test-limiter. Both experiments and simulation showed that the melting of tungsten can lead to a large material redistribution due to thermo-electron emission currents without ejection of molten material to the plasma.
TL;DR: In this paper, the multistage variational iteration method (MVIM) was used to solve a class of nonlinear systems of first-order ODEs, where the domain of validity of the solutions via the standard VIM was extended by the simple multistages strategy.
Abstract: This paper implements the multistage variational iteration method (MVIM) to solve a class of nonlinear system of first-order ordinary differential equations (ODEs). The domain of validity of the solutions via the standard variational iteration method (VIM) is extended by the simple multistage strategy. Comparisons with the exact solution and the fourth-order Runge–Kutta (RK4) method show that the MVIM is a reliable method for nonlinear equations.
TL;DR: In this article, an irreversible cycle model of a quantum heat engine with internal friction is established, which is composed of two adiabatic and two isomagnetic field processes, and the working substance of the cycle consists of an ensemble of many noninteracting spin-1/2 systems.
Abstract: An irreversible cycle model of a quantum heat engine with internal friction is established, which is composed of two adiabatic and two isomagnetic field processes. The working substance of the cycle consists of an ensemble of many non-interacting spin-1/2 systems. Based on a quantum master equation and semi-group approach, the general performance characteristics of the heat engine are investigated. The general expressions for several important parameters, such as the efficiency, power output, and rate of the entropy production, are derived. The performance of the cycle is optimized with respect to the temperatures of the working substance. By numerical solutions, the maximum power output and the corresponding parameters are calculated. The optimal regions of efficiency, temperatures of the working substance, and cycle period are determined. Moreover, the performance of the heat engine in the frictionless case is obtained, which is different from that in the friction case. Finally, the results obtained are generalized to the performance optimization of the heat engine working with spin-J systems.
TL;DR: In this paper, the effect of strontium doping on ionic conductivity of samarium-doped ceria (SDC) was investigated and the distribution and average radius of oxygen vacancies were calculated from a hard-sphere model.
Abstract: Effects of strontium doping on ionic conductivity of Sm2O3-doped ceria (samarium-doped ceria (SDC)) were investigated. The distribution and average radius of oxygen vacancies by co-doping divalent and trivalent cations were calculated from a hard-sphere model. Experimental results exhibit that the best conductivity for Ce0.78Sm0.2Sr0.02O1.88 (0.061 S cm−1) specimen is twice that of Ce0.8Sm0.2O1.9 (0.0371 S cm−1) at 800 °C. A decrease of 50 °C in the working temperature of SDC was developed by modifying the dopant concentration, average binding energy and ionic radius of the dopant. The results confirm the Sm3+ and Sr2+ co-doped ceria material as a potential electrolyte for intermediate-temperature solid oxide fuel cell applications.
TL;DR: In this article, UFG W-TiC powders with 0.25-0.8 wt% TiC additions were subjected to mechanical alloying (MA) and hot isostatic pressing (HIP), where purified H2 and Ar were used as the MA atmosphere.
Abstract: Ultra-fine grained (UFG) W–TiC with a high purity matrix of low dislocation density is expected to exhibit improve resistance to irradiation with neutrons and helium ions and the room temperature mechanical properties. Aiming at such UFG W–TiC with the desired microstructure, powders of W with 0.25–0.8 wt% TiC additions were subjected to mechanical alloying (MA) and hot isostatic pressing (HIP), where purified H2 and Ar were used as the MA atmosphere. Microstructural observations and room- and high-temperature mechanical tests were performed for UFG W–TiC before and after neutron irradiation to a fluence of 2×1024 n m−2 at 873 K. It is shown that the MA atmosphere significantly affects grain refinement, room-temperature strength and high-temperature tensile plasticity of UFG W–TiC. W–0.5TiC with H2 in MA (W–0.5TiC–H2) shows a larger strain rate sensitivity of flow stress, m, of 0.5~0.6 at temperatures from 1673 to 1973 K, which is a feature of superplastic materials. Whereas W–0.5TiC–Ar shows a smaller m value of approximately 0.2. No radiation hardening is recognized in UFG W–0.5TiC–H2 and W–0.5TiC–Ar.