Flux Pinning in Superconductors by Teruo Matsushita

By Teruo Matsushita

The publication covers the flux pinning mechanisms and houses and the electromagnetic phenomena because of the flux pinning universal for metal, high-Tc and MgB2 superconductors. The condensation strength interplay recognized for regular precipitates or grain obstacles and the kinetic power interplay proposed for synthetic Nb pins in Nb-Ti, etc., are brought for the pinning mechanism. Summation theories to derive the severe present density are mentioned intimately. Irreversible magnetization and AC loss attributable to the flux pinning also are mentioned. The loss initially stems from the ohmic dissipation of standard electrons within the basic center pushed by means of the electrical box brought about via the flux movement. The readers will study why the consequent loss is of hysteresis sort regardless of such mechanism. The effect of the flux pinning at the vortex part diagram in excessive Tc superconductors is mentioned, and the dependencies of the irreversibility box also are defined on different amounts corresponding to anisotropy of superconductor, specimen measurement and electrical box power. contemporary advancements of severe present houses in a number of high-Tc superconductors and MgB2 are brought. different subject matters are: singularity with regards to delivery present in a parallel magnetic box reminiscent of deviation from the Josephson relation, reversible flux movement inside of pinning potentials which reasons deviation from the severe country version prediction, the idea that of the minimization of strength dissipation within the flux pinning phenomena which supplies the foundation for the serious kingdom version, and so forth. major aid within the AC loss in AC wires with very advantageous filaments originates from the reversible flux movement that's dominant within the two-dimensional pinning. the concept that of minimal power dissipation explains additionally the habit of flux package measurement which determines the irreversibility line lower than the flux creep.

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For this reason the current density given by Eq. 144) is sometimes called the depairing current density. The Meissner current is another current associated with the superconducting phenomena. This current, which is localized near the surface according to Eq. 15), brings about the perfect diamagnetism. In type-2 superconductors its maximum value is Hc1 . 145) jc1 = λ Here we shall investigate the above two critical current densities quantitatively. Take the practical superconducting material Nb3 Sn for example.

7) This result is reasonable, since the energy associated with the diamagnetism is neglected in the above treatment. When H varies in space, the driving force on the flux lines in a unit volume is generally given by F d = (∇ × H) × B . 8) From Eq. 7) which disregards the effect of diamagnetism, only an electromagnetic contribution to the force appears and we have Fd ∇× B µ0 × B = J × B ≡ FL . 9) In the above, Eqs. 5) were used. The driving force F L is known as the Lorentz force. This is the force felt by moving electrons, and hence the current, in the magnetic field.

When this state is maintained steadily, an energy dissipation, and hence an electrical resistance, should appear as in a normal metal. Microscopically, the central region of each flux line is almost in the normal state as shown in Fig. 6, and the normal electrons in this region are driven by the electromotive force, resulting in an ohmic loss. This phenomenon is inevitable as long as an electromotive force exists. Hence, it is necessary to stop the motion of flux lines (v = 0) in order to prevent the electromotive force.

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