Shielding efficiency and E(J) characteristics measured on large melt cast Bi-2212 hollow cylinders in axial magnetic fields

We show that tubes of melt cast Bi-2212 used as current leads for LTS magnets can also act as efficient magnetic shields. The magnetic screening properties under an axial DC magnetic field are characterized at several temperatures below the liquid nitrogen temperature (77 K). Two main shielding properties are studied and compared with those of Bi-2223, a material that has been considered in the past for bulk magnetic shields. The first property is related to the maximum magnetic flux density that can be screened, Blim; it is defined as the applied magnetic flux density below which the field attenuation measured at the centre of the shield exceeds 1000. For a cylinder of Bi-2212 with a wall thickness of 5 mm and a large ratio of length over radius, Blim is evaluated to 1 T at T = 10 K. This value largely exceeds the Blim value measured at the same temperature on similar tubes of Bi-2223. The second shielding property that is characterized is the dependence of Blim with respect to variations of the sweep rate of the applied field, dBapp/dt. This dependence is interpreted in terms of the power law E = Ec(J/Jc)^n and allows us to determine the exponent n of this E(J) characteristics for Bi-2212. The characterization of the magnetic field relaxation involves very small values of the electric field. This gives us the opportunity to experimentally determine the E(J) law in an unexplored region of small electric fields. Combining these results with transport and AC shielding measurements, we construct a piecewise E(J) law that spans over 8 orders of magnitude of the electric field.Comment: 16 pages, 7 figure

To use or not to use cool superconductors?

The high critical temperature and magnetic field in cuprates and Fe-based superconductors are not enough to assure applications at higher temperatures. Making these superconductors useful involves complex and expensive technologies to address many conflicting physics and materials requirements

Chemical reactions and transport processes in lead iodide single crystals

Le mouvement ionique anisotrope et les propriétés de dipôle (K+-VI-), de l'ion du potassium et la vacance de l'ion d'iode, ont été étudiés en mesurant la d.c. conductivité ionique, la perte diélectrique (DL) et le thermocourant ionique (ITC). Les énergies migratoires de la VI- par l'application du champ électrique parallèle (cas I) ou perpendiculaire (cas II) à l'axe c des cristaux se sont révélés être la même valeur 0,26 eV dans les échantillons dopés K+ ions. D'autre part, l'énergie migratoire de la vacance des ions de plomb dans les cristaux dopés telle que 0,58 eV dans le cas I et 0,35 eV dans le cas II. Le maximum de DL près de 1,3 x 103 Hz se sont révélés être à 402 K. D'après les mesurages d'ITC deux courants maximums près de 167 et 185 K ont été observés. Les résultats des mesures de DL et d'ITC ont été examinés en tenant compte des facteurs préexponentiels et de l'énergie d'activation pour le saut de VI- du dipôle. Il a été trouvé que le relâchement du dipôle se compose de deux degrés.An anisotropic ionic motion and properties of potassium ion and iodine ion vacancy dipole (K+-VI-) have been studied by measuring d.c. ionic conductivity, dielectric losses (DL) and ionic thermocurrent (ITC). The migration energy of VI- by the application of the electric field parallel (case I) or perpendicular (case II) to c-axis of crystals were found to be the same value of 0.26 eV in K+-doped crystals. On the other hand, the migration energy of Pb++ ion vacancy in Bi+++-doped crystals for cases I and II were 0.58 and 0.35 eV, respectively. The DL peak near at 1.3 x 103 Hz was found at 402 K. From ITC measurements two current maxima at 167 and 185 K have been observed. The results from DL and ITC measurements were examined with respect to the preexponential factors and the activation energies for jump of VI- of dipoles. It is found that the relaxation process if dipole is composed of two stages

Improvement of Reversible Strain Limit for Critical Current of DI-BSCCO Due to Lamination Technique

The DI (dynamically innovative)-BSCCO-Bi2223 tapes achieved high critical current as well as high modulus of elasticity. Further the reversible strain limit and the corresponding stress for critical current have been remarkably increased by means of lamination technique. During the course of development, their optimized architecture has been designed based on the principle of the rule of mixture for maximizing the force free strain exerted on the superconducting component. The reversible strain/stress limit (A rev/R rev) was defined as a strain, at which the critical current recovers to the level of 99% I co. Selecting several kinds of laminating materials and changing condition of the fabrication, the excellent Cu alloy-3ply tape with I co of 311 A/cm was realized of which A rev and R rev reached 0.42% and 300 MPa, respectively. Further during the theoretical analysis, the increase of reversible strain limit were made clear to be attributed to the increase of thermally induced residual strain as well as the compensation effect of laminated layers against a local fracture mode

Longitudinal magnetization loss in twisted multifilamentary Bi2223 tape

Multifilamentary Bi2223 tapes are exposed to the longitudinal magnetic field as well as the transverse one in some electrical power apparatuses such as multilayer power transmission cables. Here, we define the longitudinal and transverse magnetic fields as the field components parallel and perpendicular to the tape axis, respectively. If the filament-bundle is twisted, it can couple to the AC longitudinal magnetic field to generate the longitudinal magnetization loss. Furthermore, the AC transport current flowing spirally in the twisted filament-bundle possibly influences the longitudinal magnetization. The longitudinal magnetization loss was measured in a twisted multifilamentary Bi2223 tape exposed to longitudinal magnetic field and carrying the transport current. The measured longitudinal magnetization loss in the twisted tape exposed to the longitudinal magnetic field is larger than that in another untwisted tape. Supplying the AC transport current changes the longitudinal magnetization loss in the twisted tape exposed to the AC longitudinal magnetic field. The influence of the transport current depends on the phase relation between the longitudinal magnetic field and the transport current. If their phase difference is 0°, the longitudinal magnetization loss decreases remarkably with increasing amplitude of the transport current. It means that the change in the current distribution due to the transport current results in the decrease in the power flow from the magnet power supply. But, a preliminary measurement of the transport loss shows that the total loss increases with increasing transport current.\ud \u

Improvement of Reversible Strain Limit for Critical Current of DI-BSCCO Due to Lamination Technique

The DI (dynamically innovative)-BSCCO-Bi2223 tapes achieved high critical current as well as high modulus of elasticity. Further the reversible strain limit and the corresponding stress for critical current have been remarkably increased by means of lamination technique. During the course of development, their optimized architecture has been designed based on the principle of the rule of mixture for maximizing the force free strain exerted on the superconducting component. The reversible strain/stress limit (A rev/R rev) was defined as a strain, at which the critical current recovers to the level of 99% I co. Selecting several kinds of laminating materials and changing condition of the fabrication, the excellent Cu alloy-3ply tape with I co of 311 A/cm was realized of which A rev and R rev reached 0.42% and 300 MPa, respectively. Further during the theoretical analysis, the increase of reversible strain limit were made clear to be attributed to the increase of thermally induced residual strain as well as the compensation effect of laminated layers against a local fracture mode