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Nonlinear simulations based on the magnetohydrodynamic model have been executed to reveal the dynamics of the ballooning mode in the spherical tokamak plasma. The simulation results have reproduced the characteristic features of the edge-localized mode crash phase, where the filamentary structures are formed along the magnetic field in the edge region, and separated from the core plasma. Moreover, the finite Larmor radius effect is addressed. [ABSTRACT FROM AUTHOR]

Abstract: The possibility of tritium self-sufficiency in a low aspect ratio (low-A) tokamak reactor with the outboard blanket only has been studied to simplify the inboard structure located in a high magnetic field. The tritium breeding ratio (TBR) of the outboard blanket increases by applying a neutron multiplier such as lead and beryllium to the inboard reflector. The effect in local TBR of a 40cm thick inboard reflector of lead is about 40% that of the inboard breeding blanket. The local TBR of a reactor with both the lead inboard reflector and outboard blanket using a Li2O breeder and a beryllium multiplier can be larger than 1.35 for aspect ratios less than 2.9. The local TBR of 1.35 satisfies the net TBR requirement of 1.05 where there is 78% coverage of the breeding zone over the total plasma-facing surface area. The result indicates there is a design solution achieving tritium self-sufficiency even in a low-A tokamak reactor with the outboard breeding blanket only, using an appropriate inboard reflector. Be12Ti and Li2TiO3 are recommended from the viewpoint of safety. In the combination, the aspect ratio is required to be less than 1.35 to achieve local TBR of 1.35. [Copyright &y& Elsevier]

Abstract: An HTS SQUID probe microscope has been developed using a high-permeability needle to enable high spatial resolution measurement of samples in air even at room temperature. Image processing techniques have also been developed to improve the magnetic field images obtained from the microscope. Artifacts in the data occur due to electromagnetic interference from electric power lines, line drift and flux trapping. The electromagnetic interference could successfully be removed by eliminating the noise peaks from the power spectrum of fast Fourier transforms of line scans of the image. The drift between lines was removed by interpolating the mean field value of each scan line. Artifacts in line scans occurring due to flux trapping or unexpected noise were removed by the detection of a sharp drift and interpolation using the line data of neighboring lines. Highly detailed magnetic field images were obtained from the HTS SQUID probe microscope by the application of these image processing techniques. [Copyright &y& Elsevier]

Abstract: We numerically calculate total AC losses in a single Bi-2223 tape carrying a transport current in an external magnetic field parallel or perpendicular to the tape face. We also carry out the calculations for two models of three-strand parallel conductor. One is without transposition, and the other is with optimum transposition so that the branch current in each strand becomes equal. It is confirmed the total AC losses fairly increase with the simultaneous application of transport current. It is also found that in the perpendicular field the total losses are scarcely dependent on transposition but on the number of strands in the smaller field amplitude. In the parallel field, the effect of the number of strands on the total AC losses is notable as well as transposition. [Copyright &y& Elsevier]

Abstract: AC losses are numerically evaluated in thin superconducting tapes exposed to an external magnetic field perpendicular to their broad face under the assumption of the critical state model including the field dependence of a critical current density. When the thickness of tape is much smaller than the width, the electromagnetic fields are determined by obtaining the distribution of the magnetic field perpendicular to the tape face and the current density integrated over the tape thickness. Nonlinear integral equations for the perpendicular field are numerically solved at each step during a cycle of external field, and the magnetization losses are finally estimated from the product of local electric field and current density. The influences of the field dependence of critical current density on the losses are discussed quantitatively. [Copyright &y& Elsevier]

We have numerically and experimentally studied on the Josephson-vortex flow in stacks of intrinsic Josephson junctions in Bi2Sr2CaCu2Oy single crystals. Numerical simulations of static and dynamic behavior of Josephson vortices in such a stack were carried out by using perturbed coupled sine-Gordon equations. The current-voltage characteristics of the stacks in the single-crystal mesas were measured without or with magnetic field B up to 4.5 T parallel to the junction layers at 4.2 K. It has been observed that the vortex flow tends to occur preferably in the highest velocity mode (in-phase mode) only in several junctions in the stack in low B below ∼ 1 T, in intermediate velocity modes in more junctions in it in intermediately higher B and preferably in the lowest velocity mode (out-of-phase mode) in almost all junctions in it in much higher B above ∼2.5 T, accompanied by a decrease in flow velocity from ∼ 2.5 × 106 to (2-5) × 105 m/s with increasing Bfs. This behavior of vortices can be interpreted to arise from an increase in interaction among vortices in the stack with the increase in B, according to the simulated results. [ABSTRACT FROM AUTHOR]

In order to reproduce the experimental results of AC losses in a Bi-2223 Ag-sheathed tape exposed to the external magnetic field with an arbitrary angle to the broadest face, we calculate the AC losses by means of the two-dimensional finite element method that directly analyzes the magnetic field distribution around the wire. It is assumed that the voltage–current characteristics are represented by the power-law model including the dependence of both the critical current density and n-value on an effective perpendicular component of applied magnetic field. The obtained numerical results have a good agreement with the experimental results in the large amplitude of applied magnetic field. [Copyright &y& Elsevier]

AC losses are numerically evaluated in superconductors with a rectangular cross section and an infinite length for the application of either transport current or external magnetic field perpendicular to the broadest face. It is assumed that the electromagnetic response is determined by Bean''s critical state model, in which the critical current density is independent of the magnitude of local magnetic field. In this case, the AC loss per cycle can be estimated directly from the magnetic-flux distribution inside the superconducting wire at the peak of cyclic field. By investigating the influence of the aspect ratio of wire cross section on the losses, it is concluded that conventional expressions for a strip are almost applicable to a very thin but finite wire. [Copyright &y& Elsevier]

The influence of effective vacuum part is numerically evaluated on AC losses in superconducting wires calculated by means of a two-dimensional finite element method, which is formulated with a self-magnetic field due to an induced current as unknown. In the present method, the high-resistivity metal around the wires is needed for the sake of the simplicity in program coding. The superconducting wires carry an alternating transport current or are exposed to an external AC magnetic field. The AC losses are numerically calculated for square and circular effective vacuum parts with wide ranges of the sizes and the resistivity. Relative errors in the obtained results are discussed as compared with conventional analytical predictions. [Copyright &y& Elsevier]

Magnetization and magnetoresistance of A-type antiferromagnet Pr0.45Sr0.55MnO3 have been measured by means of pulsed magnetic fields up to 45 T. Below TN∼215 K, metamagnetic transitions and attendant discontinuous decreases in resistivity were observed. Above the transition fields, the transport anisotropy is reduced compared with that in the antiferromagnetic state. The observed ferromagnetic transition and resistivity change indicate the simultaneous collapse of spin and orbital order by magnetic field. [Copyright &y& Elsevier]

Investigates the formation of a magnetic field found in the Magnetic Reconnection Experiment (MRX) by a magnetohydrodynamic relaxation theory and a numerical simulation. Growing process of the island into a spheromak-type configuration; Types of injection mode of a toroidal field in the MRX.

Discusses the role of singular currents in three-dimensional toroidal equilibria and their resolution by magnetic island formation. Importance of current sheets recognized in analytical theories; Comparison of the predictions of the theory with the numerical results from the HINT code.

Examines the behavior of magnetic islands and their effect on plasma confinement. Simulations of three-dimensional equilibria in the H-1 Heliac; Evolution of a rotational transform to exclude the rational surface concerned; Evidence of near-resonant flux surface deformations.

Analyzes the behavior of finite-pressure-induced magnetic islands for three-dimensional magnetohydrostatic equilibria of the Helias configuration. Use of a three-dimensional equilibrium code; Remarkable property of magnetic islands induced by the finite pressure effect; Numerical scheme of HINT.

A central theme of ``Complexity?? is the question of the creation of ordered structure in nature (self-organization). The assertion is made that self-organization is governed by three key processes, i.e., energy pumping, entropy expulsion and nonlinearity. Extensive efforts have been done to confirm this assertion through computer simulations of plasmas. A system exhibits markedly different features in self-organization, depending on whether the energy pumping is instantaneous or continuous, or whether the produced entropy is expulsed or reserved. The nonlinearity acts to bring a nonequilibrium state into a bifurcation, thus resulting in a new structure along with an anomalous entropy production. As a practical application of our grand view of self-organization a preferential generation of a dipole magnetic field is successfully demonstrated. [ABSTRACT FROM AUTHOR]

Microfission chambers, which are pencil sized ionization chamber containing fissile material inside, will be installed in the vacuum vessel as neutron monitors for International Thermonuclear Experimental Reactor (ITER). We have performed first measurements of the detector installed between the vacuum vessel and toroidal coils on JT-60U. The technical validity as a neutron monitor, such as magnetic field effect and electromagnetic noises from the plasma and heating devices, has been investigated. The detector had an excellent linearity with a 235U fission chamber as a neutron monitor on JT-60U with the standard deviation of 3% except for some noise signals. The electromagnetic noises were caused by neutral beam injection (NBI) breakdowns, probably due to long wiring between the detector and the preamplifier. In case of plasma disruption, improper signals have not been observed. The magnetic field effect also has not been observed up to 2 T. In JT-60U, we confirmed availability of the micro fission chamber as a neutron monitor over three decades of neutron source strength up to 1.3×1016 neutrons/s with 1 ms temporal resolution. The biggest weakness in the detector was its noise sensitivity to NBI breakdowns. Therefore, by suppressing the electromagnetic noise, microfission chambers can be available as neutron monitors for ITER. [ABSTRACT FROM AUTHOR]