For the intermediate state of Type I superconductors described in chapter 5 to exist stably, the boundary energy of the superconducting and normal regions must be positive because a negative boundary energy will induce fine division of the normal and superconducting regions immediately on entrance to the intermediate state to lower the energy as a whole. Magnetic properties and direct observation of the intermediate state show that this is not the case. The London theory, which assumes that the number of superelectrons is constant throughout the superconducting region, gives only a negative boundary energy because of the penetration of the magnetic field passing through the normal region which lowers the magnetic energy of the superconducting region. In the Ginzburg-Landau (GL) theory, however, the number of superelectrons is allowed to change over a coherence length ξ. Therefore, in contrast with the London theory where the number of superelectrons must decrease to zero stepwise at the boundary, the GL theory shows that the number of superelectrons near the boundary may decrease continuously to zero over the coherence length. The decrease of the number of superelectrons will give rise to a positive energy contribution to the boundary energy as a result of the loss in the superconducting condensation energy. It is shown that the boundary energy may be positive or negative, depending on the magnitude of the GL parameter κ=λL/ξ, where λL is the London penetration depth.
The cryogenic tensile behavior of SL-ES30 woven glass-epoxy laminates has been discussed through theoretical and experimental characterizations. The tension tests were conducted in accordance with JIS K 7054 at room temperature and liquid nitrogen temperature (77K). The general specimen geometry was a rectangular dog-bone shape with constant gage length, but with each specimen size having a different specimen width. The experimental finding provides the data for analytical modeling. The model uses two damage variables that are determined from experimental data. A finite element method coupled with damage was adopted for the extensional analysis. The effects of temperature, specimen geometry and gripping method on the tensile properties are examined.
NbTi superconducting multilayer rolled sheet with Nb layers for artificial pinning centers can be manufactured using Cu alloy hardened by precipitation as intermittent layers. The total number of Nb layers is 580, that of NbTi layers is 551, that of Cu-3Ni-0.6Si-0.2Zn intermittent layers is 28 and that of Cu layers is 2 (only outside). The global pinning force Fp value of the multilayer sheet 40μm in total thickness cut widthwise is about 15GN/m3, while the magnetic field is 1T. This value is comparable with those of superconducting multifilamentary wires with artificial pinning centers. But Fp values when the magnetic field is above 3T are almost the same as those of conventionally aged sheets. The Nb layers for artificial pinning centers are effective at 3T and below 3T in a comparatively low magnetic field. According to the relationship between Fp values and the measured thicknesses of Nb and NbTi layers, Nb layers do not have much effect as artificial pinning centers until their thickness is less than 100nm. When the mean thickness of the Nb layers is 95 to 33nm, the magnetic field where the Fp value reaches the maximum is kept around 1T. The maximum Fp value is obtained when the mean thickness of the Nb layers is 39nm. The restacked multilayer sheet, 80μm in total thickness and 29nm in mean thickness of the Nb and NbTi layers, is manufactured by combining the former two multilayer sheets. The magnetic field where the Fp value reaches the maximum in this restacked multilayer sheet is shifted by 0.5T to 1.5T from 1T going toward the higher magnetic field range, and the Fp value at 3T also increases to about 10GN/m3, which is considerably high compared with that of the conventional sheets. According to this result the large-size multilayer sheet with a strong pinning force in higher magnetic fields could be manufactured by the rolling method if the final total thickness of the sheet and the thicknesses of Nb and NbTi layers are optimized.