This commentary notes give brief discussion on material properties of high temperature superconductors from the aspect of suitability to the field effect device application and on principle concerning the modulation of superconductivity. Some examples of the drain current modulation in the test devices, YBCO-MISFETs, are shown. However, the actual data taken from the MISFETs are far from the goal. The major cause for this is arising from the degraded interface between YBCO channel layer and gate insulator. First measurement of the interfacial diffusion was carried out and some favorable combination of the gate insulator and YBCO channel is proposed.
Recent progress in the synthesis and the study on superconducting properties of Hg-based cuprates superconductors, HgBa2Ca(n-1)CunO2+2n+δ, is reviewed. An encapsulation and singlefiring (ECSF) technique is successfully utilized for the preparation of nearly single-phase samples of the Hg-based cuprates superconductors. Superconducting transition temperature, Tcmag, is enhanced to a record high value of -136K for a nearly single-phase Hg-1223 (n=3) sample. Physical properties, e.g.Tc, Jc and Hc, of the Hg-12 (n-1)n superconductors are compared with those of other known cuprate superconductors.
Superconducting coil has been developed for various types of demand. Especially for nuclear fusion application, we need very high magnetic field and hence large coil. For the purpose of applying it, it is very important to know the detail of the deformation of the conductor to make an exact control of the magnetic field. Mito made some tests on a small superconducting helical coil (11th International Conference on Magnet Technology (1989) 783). The coil we work in this time is solenoid type and has the same cross section, number of layers and winding curve as Mito's helical one. We investigated more detailed strain behavior and compared the data of solenoid with that of helical coil, and found that the shape of helical gave larger strain in windings. Thus we see the much dependence of the strain value on the winding type. By the way, some parts of a coil showed an irregular behavior in spite of the axisymmetric electromagnet force. Such behavior is specific to the each coil, because the coil seemed to have its own initial imperfection or load record during fabrication. This is result of small solenoid coil. But, in practice, to excite very large and complicated shape coil, we have to give more attention to initial imperfection or load history.
In this paper, we consider the transient thermal-mechanical stress ploblem of cracked woven glass-epoxy laminates with temperature-dependent properties. The woven composite is suddenly cooled at the surfaces. The composite material in generalized plane strain is assumed. Finite element method is used to study the influence of weave curvature and crack formation on the thermal shock behavior of G-10CR glass-epoxy laminates at low temperatures. Numerical results on the transient temperature and thermal-mechanical stress distributions are obtained and are presented in a graphical form.
V3Si multifilamentary superconductors produced by a modified bronze process are promising for AC applications. The combination of adjusting the total proportion of V to Si in the Cu-Si/V composite to -3 and reducing V filaments to -1μm enables the completion of the reaction in a short time; the V5Si3 initially formed around V3Si filaments appropriately decomposes and mostly V3Si without grain growth is produced to achieve a high overall critical current density Jc. In addition to fine grain structure of V3Si, an increment in density of V3Si/normal-metal interface pinning center is also responsible for the high overall Jc of 1.3×109A/cm2 at 5T, being comparable to that of Nb3Sn multifilamentary wires produced by the bronze process for AC use. The resistivity of remaining V5Si3 layers (-15μΩcm at 4.2K) is likely to be high enough to separate the filaments from each other for electromagnetic decoupling. The effective filament diameter Deff in fields ranging from 1.5 to 7T was -3.5μm for 1.2μm (the designed V filament diameter before heat treatment) composites with undecomposed V5Si3 layers, being one of the smallest Deff reported so far for AC Nb3Sn superconductors. Disappearance of V5Si3 layer after long heat treatments increased Deff, suggesting that the existence of V5Si3 layer is effective to reduce Deff. Thus, with optimal cross-sectional structure (bronze composition, overall V/Si ratio, filament spacing, filament size, etc.), the control of thickness and morphology of V5Si3 layer would furthermore reduce Deff and hence AC losses.
In order to evaluate the fracture toughness of CSUS-JN 1 austenitic stainless steel rolled plate for superconducting magnet structures of magnetic fusion reactors, we have performed elastic-plastic fracture toughness testing at 4.2K. 1T compact test specimens and computer controlled unloading compliance method are used for the JIC tests. The effects of specimen thickness and side-groove on JIC and Tmat are examined. SEM fractograph reveals the effect of specimen thickness on fracture surface. The effect of crack tunneling on determination of J-R curve and JIC, and a difference between ASTM E 813-81 and E 813-87 are also discussed.