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An optimization design method of short-length actively shielded and open structure, superconducting MRI magnets is suggested in the paper. Firstly, the section of the solenoid coil is simplified as a current loop with zero section to solve a linear programming problem. The position coordinates in the radius and axial, and current for the loop can be calculated by the linear programming method. Then, the cross-section of the coil is optimized with a genetic algorithm to get appropriate section size. The method of linear programming, especially combining with genetic algorithm, reduces optimizing variables, which makes the design of a magnet feasible. Based on the method, a full open MRI superconducting magnet is designed with maximum radii of 0.8 m and 1.2 m. In the paper, the detailed optimization technologies are presented. [ABSTRACT FROM AUTHOR]

There are a lot of experimental reports on the scaling of flux pinning in the form of F : Fmbl/2(1 - b)2, with b = B/Bc2. The temperature dependence of Fm is approximately proportional to B[(Multiple line equation(s) cannot be represented in ASCII text)], whereas the strain dependence of Fm is reported to be proportional to the upper critical field Bc2. In this work, we re-analyze our previous data with the Kramer model including the pin-breaking dynamic pinning force (Fp) for a low field region. It is shown that the extrapolated upper critical field B*c2, strongly depend on the ratio between the mean of the parameter Kp for Fp (< Kp >) and the parameter Ks for the flux line lattice shearing pinning force Fs. It is found that the strain dependence of Fm at 4.2 K is approximately proportional to (B*c2) 1.5. We further compare the data with the prediction of our recent scaling theory based on Eliashberg theory of strongly coupled superconductors. It is shown that the strain dependence of Fm at 4.2 K is proportional to B[(Multiple line equation(s) cannot be represented in ASCII text)] κ-2, consistent with the temperature dependence of Fro. Moreover, this model agrees reasonably well even with the data in a high compressive strain region (<-0.8%). [ABSTRACT FROM AUTHOR]

We report detailed magnetization measurement results for two internal-tin Nb3Sn strands. The paramagnetic background of a Mitsubishi strand is about 4 times larger than that of a KAT strand below the transition temperature, which can be understood as combined effects of Pauli and Langevin paramagnetism. From magnetic relaxation measurement for the KAT strand, a possibility of surface barrier effect is discussed. After subtracting the paramagnetic background, reversible magnetization data are analysed using the Hao-Clem model and the Ginzburg-Landau parameters (κ), the thermodynamic and the upper critical fields (Bc, Bc2) at various temperatures are obtained. The temperature dependences of κ, Bc and Bc2 are compared with the recent theoretical calculation results for Nb3Sn and also with widely used empirical formulas. [ABSTRACT FROM AUTHOR]

The development of a high performance superconducting magnet requires a thorough understanding of the strain effect in the critical current density (Jc) of Nb3Sn strands. A modified version of the WASP device is used for the investigation of the strain effect. The spring is made of BeCu alloy and is capable of applying strain up to 0.7% reversibly at 4.2 K. Several types of high performance Nb3 Sn strands (Jc > 1000 A/mm² at 12 T and 4.2 K) have been developed using internal tin process. A comparative study on the axial strain dependence of the critical current is performed. [ABSTRACT FROM AUTHOR]

The Korea superconducting Tokamak Advanced Research (KSTAR) device, a steady-state-capable advanced Tokamak, is to be built in Korea. The KSTAR device is made up of 16 toroidal field (TF) and 14 poloidal field (PF) superconducting coils. A simulation code for the transient operation of the KS TAR TF and PF coils is developed. For stable Tokamak operation, the operating characteristics of the KSTAR superconducting magnet system are studied for operation scenario. We calculated the temperature margin of superconducting cables, cryogenic flow parameters and the heat deposition in TF and PF coils. The effect of the three-dimensional heat conduction and the eddy current loss in the supporting structure and vacuum chamber of KSTAR is also included. [ABSTRACT FROM AUTHOR]

The properties of the magnetic materials, such as the amorphous alloys and the grain-oriented silicon steels, are essential to the design of high-temperature superconducting transformers. In this paper the magnetic properties and the loss characteristics of different ferromagnetic materials are measured at liquid nitrogen temperature. It is shown from experimental results that at 77 K the saturation flux density of the amorphous metal is about 0.3 T lower than that of the silicon steel, and the loss of amorphous metal is 4 times less than that of the silicon steel. Since the losses of materials at 77 K are higher than those of at room temperature, it is not economical to immerse the transformer core in liquid nitrogen. [ABSTRACT FROM AUTHOR]

The leakage magnetic field in HTS transformer windings fabricated by Bi-2223 tapes decreases the critical current and increases the ac losses in the tapes. Because of the anisotropy of the HTS tape, the numerical analysis of the radial component of the leakage field is especially important. In this paper the influence of the core structure and the winding configuration on the stray field is studied by finite element method, and some suggestions for improving the leakage field distribution are presented to make HTS transformers more efficient. [ABSTRACT FROM AUTHOR]

Abstract: A comparative study on the effects of heat treatment, especially, the duration of the A15 reaction temperature plateau on the strain dependence of the critical current for an internal-tin processed Nb3Sn strand has been carried out. The strain dependence of the critical current is measured by a variable temperature Walter spiral probe that we have developed. It was shown that prolonged heat treatment can be a very effective way to improve the strain dependency. For a quantitative analysis, the measured data were analyzed with various proposed scaling laws: the scaling law based on strong-coupling theory, the modified deviatoric strain scaling law, and the interpolative scaling law. We found that there is a slight increase in the critical temperature and a substantial improvement in the maximum pinning force. The origin of improved strain dependency is further discussed. [Copyright &y& Elsevier]