Search

A special pancake coil is designed and manufactured by using Bi-2223/Ag tape in order to measure the magnetic field between some turns of it using the Hall probe. The studies have shown that the sheet critical current density across the tape is non-uniform.

The radial component of the magnetic field produced by the pancake coil wound with an YBCO coated conductor is measured near the cross-section of the winding. The exact current distribution in the winding cross-section is approximated and the results are expressed for different coil currents during a gradual ramping up and down.

The properties of coils made out of the second generation superconducting wire are studies by designing and testing an experimental double pancake coil wound with copper stabilized YBCO coated conductor. The studies haves shown that the YBCO double pancake coil was able to operate at AC currents with frequencies up to 864 Hz and amplitudes close to the coil critical current.

The analysis of the transport and magnetic properties is employed for the characterization of the individual filaments in a multifilamentary YBCO coated conductor. The results show that the values of the filament critical current and the n-factor vary largely with the filament.

A study compared Hall probe measurements made above three Ag/BSCCO-2223 tapes of multifilamentary, multilayer configurations and carrying AC and DC transport currents. Magneto-optical measurements made at intermediate frequencies on two of the tapes with magnetic fields applied perpendicular to the tape plane are also presented. Among other results, DC transport current Hall probe measurements should not be extrapolated to AC losses without some caution because of time dependence.

It is well established that near the silver interface highly textured Bi-2223 layers compared to the inner ceramic core may be obtained. Thus Bi-2223 multilayered concentric tapes with silver matrix are very promising in increasing transport critical current densities. In the present work we report on the electromagnetic characterization of short tapes having in their cross-section a very thin HTS flattened ring with Ag inside and outside of it. The samples were prepared by the powder in tube method and have self-field critical current densities [J.sub.c] of the order of 3x[10.sup.4] A/[cm.sup.2] at 77 K. Transport and SQUID magnetization measurements revealed weak link nature of the samples in low magnetic fields. Large transport [J.sub.c](B) hysteresis was observed at 4.2 K and magnetic fields up to 20 T. Magnetic field profiles measurements with miniature Hall sensors are in qualitative accordance with model calculations supposing homogeneous current density distribution across the superconducting core.

The use of two coaxial ac coils is proposed as a means of solving the problem of ac-dc coil coupling in apparatus used to carry out loss and magnetization measurements. The approach has been implemented in a dc-ac superconducting magnet system for operation at 50 Hz and 60 Hz. The instrument generates an ac field ranging from 0.4 T to 1.1 T which is superimposed on a dc magnetic field of up to four tesla.

A 14 kVA superconducting transformer with Bi-2223/Ag windings is tested.

The influence of ferromagnetic rings (FR), attached to the ends of a test coil wound with Bi-2223/Ag tape, on AC losses in the coil is investigated.

A heat-shrink tube insulation for second-generation high-temperature superconducting (2G HTS) coils is studied experimentally in this paper. The insulation can be used to prevent the delamination of 2G HTS due to epoxy impregnation. According to the experiment results, the insulated coil shows no degradation before and after the epoxy impregnation. To validate the performance of 2G HTS coils with the heat-shrink insulation, we measured the transport loss, magnetization loss and total loss of a 2G HTS coil. The study demonstrates the feasibility of the heat-shrink tube insulation method for electrical applications. [ABSTRACT FROM PUBLISHER]

A finite element model for a YBCO pancake coil with a magnetic substrate is developed in this paper. An axial symmetrical H formulation and the E-J power law are used to construct the model, with the magnetic substrate considered by introducing an extra time-dependent term in the formula. A pancake coil is made and tested. The measurement of critical current and transport loss is compared to the model result, showing good consistency. The influence of magnetic substrate in the condition of AC and DC current is studied. The AC loss decreases without a magnetic substrate. It is observed that when the applied DC current approaches the critical current the coil turn loss profile changes completely in the presence of magnetic substrate due to the change of magnetic field distribution. [ABSTRACT FROM AUTHOR]

In this paper we discuss the predictive analysis performed in support of the test program of the International Thermonuclear Experimental Reactor (ITER) Poloidal Field Conductor Insert (PFCI). A subset of the test program items was considered, with particular emphasis on DC performance and AC losses. The results and implications of the comparison of selected predictions from different laboratories will be presented. [ABSTRACT FROM AUTHOR]