Critical current measurement of commercial REBCO conductors at 4.2 K

REBCO coated conductors are now available from several industrial manufacturers and are expected to be promising conductors for high-field-magnet applications. Using these conductors, the development of solenoids capable of generating high magnetic fields of 20–30 T is ongoing in major high-field laboratories in the world. In addition, CERN recently launched a conceptual design study for the Future Circular Collider, in which a 20-T dipole magnet is listed as a candidate for the bending magnet of the main ring. However, there has been limited research published on the electrical transport properties of commercially available REBCO conductors in a high-field, low-temperature environment. For magnet designers, the transport properties are of the highest importance in choosing a suitable conductor, and the data form the bases for high-field magnet development. Therefore, in this work, a new sample holder, which allows the measurements of full-width conductors to be carried out relatively easily, was developed, and the transport properties of commercial REBCO conductors from seven manufacturers (AMSC, Fujikura, Shanghai Superconductor, SuNAM, SuperOx, SuperPower, and SWCC Showa) were investigated at 4.2 K in perpendicular fields of up to 18 T. The results show that the I_c values at 4.2 K clearly vary to some extent among these commercial conductors and the higher-current 4-mm-wide conductors have I_c values in the range of 230–305 A at 18 T and in the range of 320–424 A at 12 T.     

The possibility of increasingTc in oxide high-Tc superconductor films: Interaction with elastic fields of defects

The influence onT _c of dilatation centers (DC) as elastic defects near the surface or in thin films of oxide high-T_c superconductors is considered. The distribution function ofT _c in this case was obtained. This is the Lorentzian with center shifted to largerT _c values. The half width of theT _c distribution n (n is the concentration of DC) is larger than its center shift and corresponds to the increase ofT _c fluctuations near the surface. As a result, a continuum percolation behavior with increasing critical temperature percolation levelT ^(c) near the surface appears. The inequalityn>T ^(c)>T _c ^initial is fulfilled. ForT>T ^(c) the quasi-2D Josephson media takes place where a finite superconductive domain withT _c ^local >T ^(c) exists. The influence of DC considerably increases for strong DC such as off-center impurity ions.     

The angular dependence of AC losses in BSCCO/Ag tapes under AC magnetic fields and AC transport currents

The measurement results of AC transport current losses in BSCCO/Ag tapes caused by AC transport currents and the simultaneously presented AC magnetic fields were reported. The measurements were carried out at 77 K and power frequency (50 Hz) for AC applied magnetic fields of 48, 80 and 120 mT, respectively. The angle between the direction of the magnetic field and the wide side of the tape varied from 0° to 90° with a step of 10°. Analyses on the angular dependency of the AC losses for BSCCO/Ag tapes were given. A theoretical model to describe the angular dependency of AC losses was proposed and compared with the experimental results.     

Spatial distribution of the local resistive transition and the critical current density in YBCO coated conductors using Low-temperature Scanning Laser Microscopy

Low-temperature Scanning Laser Microscopy (LTSLM) was carried out to reveal the spatial distribution of the local resistive transition temperature and the local current density in commercial YBCO coated conductors near the superconducting transition. The result of the sample with an array of holes of various sizes shows that the signal δV is proportional to the current density. The distribution of the critical temperature of the sample with two parallel bridges is quite homogeneous and the transport current flows mainly along the outer edge of the sample. Using LTSLM we directly image the current path in YBCO coated conductors of different patterns.     

Testing of strain-gauge pressure transducers up to 3.5 MPa at cryogenic temperatures and in magnetic fields up to 6 T

The characteristics of four commercial strain-gauge pressure transducers suitable for measurements in a temperature range from 4.2 to 293 K were determined in the presence of magnetic fields up to 6 T. The highest pressure measured was 3.5 MPa. Tests showed that if the transducers are used in these conditions and no corrections are made, uncertainties up to 19% of the transducer full scale may be inherent in measurements. When such high error levels are unacceptable, the transducers must be individually calibrated under the working conditions: in this way the uncertainties in pressure measurements can usually be kept below 1 % of the transducer full scale.     

Ability of a contactless inductive device for the characterization of the critical current versus temperature in superconducting rings at temperatures close to TC

Critical current measurements for three polycrystalline rings of YBCO, three Bi-2223, and one YBCO + Ag were developed from a temperature close to 80 K to the critical temperature using a previously reported contactless inductive device based on the transformer method. These data were used to analyze the ability of this device to characterize, in superconducting rings, the Ginzburg-Landau, Ambegaokar-Baratoff, and De Gennes regimes as well as the crossover temperature between them.     

Advances in piezoelectric thin films for acoustic biosensors,acoustofluidics and lab-on-chip applications

Recently, piezoelectric thin films including zinc oxide (ZnO) and aluminium nitride (AlN) have found a broad range of lab-on-chip applications such as biosensing, particle/cell concentrating, sorting/patterning, pumping, mixing, nebulisation and jetting. Integrated acoustic wave sensing/microfluidic devices have been fabricated by depositing these piezoelectric films onto a number of substrates such as silicon, ceramics, diamond, quartz, glass, and more recently also polymer, metallic foils and bendable glass/silicon for making flexible devices. Such thin film acoustic wave devices have great potential for implementing integrated, disposable, or bendable/flexible lab-on-a-chip devices into various sensing and actuating applications. This paper discusses the recent development in engineering high performance piezoelectric thin films, and highlights the critical issues such as film deposition, MEMS processing techniques, control of deposition/processing parametres, film texture, doping, dispersion effects, film stress, multilayer design, electrode materials/designs and substrate selections. Finally, advances in using thin film devices for lab-on-chip applications are summarised and future development trends are identified.