Flux Pinning in Superconductors

Superconductivity is now a considerable focus of attention as one of the te- nologies which can prevent environmental destruction by allowing energy to be used with high e?ciency. The possibility of practical applications of sup- conductivitydependsonthemaximumcurrentdensitywhichsuperconductors can carry, the value of losses which superconductors consume, the maximum magnetic ?eld strength in which superconductors can be used, etc. These f- tors are directly related to the ?ux pinning of quantized magnetic ?ux lines in superconductors. This book extensively describes related subjects, from the fundamental physics of ?ux pinning to electromagnetic phenomena caused by ?ux pinning events, which will be useful for anyone who wants to understand applied superconductivity. The Japanese edition was published for this purpose in 1994. Since then, there has been signi?cant progress in the research and development of hi- temperature superconductors. In particular, the new superconductor MgB 2 was discovered in 2001, followed by steady improvements in the superc- ducting properties necessary for applications. On the other hand, there are no essential di?erences in the ?ux pinning phenomena between these new superconductors and metallic superconductors. Hence, the framework of the previous Japanese edition was kept unchanged, while new description was added on these new superconductors in the English edition. In the following the content of each chapter is brie?y introduced.

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The book covers the flux pinning mechanisms and properties and the electromagnetic phenomena caused by the flux pinning common for metallic, high-Tc and MgB 2 superconductors. The condensation energy interaction known for normal precipitates or grain boundaries and the kinetic energy interaction proposed for artificial Nb pins in Nb-Ti, etc., are introduced for the pinning mechanism. Summation theories to derive the critical current density are discussed in detail. Irreversible magnetization and AC loss caused by the flux pinning are also discussed. The loss originally stems from the ohmic dissipation of normal electrons in the normal core driven by the electric field induced by the flux motion. The readers will learn why the resultant loss is of hysteresis type in spite of such mechanism. The influence of the flux pinning on the vortex phase diagram in high Tc superconductors is discussed, and the dependencies of the irreversibility field are also described on other quantities such as anisotropy of superconductor, specimen size and electric field strength. Recent developments of critical current properties in various high-Tc superconductors and MgB 2 are introduced. Other topics are: singularity in the case of transport current in a parallel magnetic field such as deviation from the Josephson relation, reversible flux motion inside pinning potentials which causes deviation from the critical state model prediction, the concept of the minimization of energy dissipation in the flux pinning phenomena which gives the basis for the critical state model, etc. Significant reduction in the AC loss in AC wires with very fine filaments originates from the reversible flux motion which is dominant in the two-dimensional pinning. The concept of minimum energy dissipation explains also the behavior of flux bundle size which determines the irreversibility line under the flux creep.

Contenu
Introduction.- Fundamental Electromagnetic Phenomena in Superconductors.- Various Electromagnetic Phenomena.- Longitudinal Magnetic Field Effect.- Measurement Methods for Critical Current Density.- Flux Pinning Mechanism.- Flux Pinning Characteristics.- High-Temperature Superconductors.- MgB2.- A1 Description of Equilibrium State.- A2 Magnetic Properties of a Small Superconductor.- A3 Minimization of Energy Dissipation.- A4 Partition of Pinning Energy.- A5 Comments on the Nonlocal Theory on the Elasticity of the Flux Line Lattice.- A6 Avalanching Flux Flow Model.- A7 Josephson Penetration Depth.- A8 Transverse Flux Bundle Size.