Guo Min Zhang

Design and performance of a small HTS bulk reluctance motor

HTS bulks can be used as flux-focusing elements in reluctance motors. As parts of the primary study, a small prototype reluctance motor was designed and constructed by using HTS YBCO bulks. The performance was analyzed based on magnetic field calculation. An experimental investigation was carried out on the prototype motor. Computed parameters are compared with test measurements, showing good agreement. Compared with the conventional synchronous reluctance motors, higher efficiency and smaller size make these motors very attractive for the applications, such as cryogenic pumps and flywheel drives.

Performance of

The voltage and temperature of YBa2Cu3Ox (YBCO) tapes with different structures were measured at alternating-current overcurrent conditions in liquid nitrogen. A safety temperature limit of the tapes with different structure was obtained based on the measured critical-current degradation data of the YBCO tapes. According to heat conduction model, the electrical and thermal performances of YBCO tapes were analyzed for tapes with different stabilizers. The comparison was presented for simulation and test data. The results are helpful for the design of superconducting electrical equipment.

\hbox{YBa}_{2}\hbox{Cu}_{3} \hbox{O}_{x}

A theoretical model describing the angular dependence of critical current was proposed based on the critical state model and the effective mass theory. The critical currents of single-tape and a stack of three BSCCO/Ag tapes were measured under DC magnetic fields with different orientations and strength. The comparison of the theoretical and experimental results is presented.

Tapes With Different Structures Under AC Overcurrent Conditions

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.

A theoretical model for the angular dependence of the critical current of BSCCO/Ag tapes

Magnesium diboride (MgB2) shows a wide application prospect in the field of low field DC application for its relatively simple structure and rather higher critical temperature than LTS. With the development of MgB2 composite superconductor manufacturing technology and cryogenic technology, developing conduction cooled superconducting MRI system with MgB2 composite superconductor is becoming increasingly feasible. An MgB2 superconducting magnet for MRI was developed. The MgB2 superconducting magnet is used to investigate the fundamental scientific problem of the MRI main magnet, including field uniformity and stability, influencing factors of MgB2 composite superconductor on field uniformity and stability. The superconducting magnet consists of 2 solenoids wound with MgB2 wire with the length of 60 m. The magnet has an outer diameter of 169 mm, an iron core diameter of 135 mm, and air gap of 32 mm. The superconducting magnet is fabricated and tested. The central magnetic field reaches 1.0 T when the current of the MgB2 magnet is 290 A. The central magnetic field is 0.39 T when the current of the MgB2 magnet is 100 A. In this paper, the minimum quench energy, the quench propagation velocity and the minimum propagation zone of the MgB2 composite conductor are measured. Main magnet for MRI with MgB2 composite superconductor is analysed and proposed, including magnet design and test results. By theoretical modeling and simulation, the detailed quench propagation of the magnet is further analysed. Finally, the stability criteria of conduction-cooled MRI magnet are established.

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

Practical applications of HTS tapes cannot avoid various stresses and strains, including tension, bending and/or torsion. These loads directly affect the critical current and AC losses of HTS tapes. Thus the investigation of the effect of stress/strain on HTS tapes is important for practical applications. Here, the critical currents and AC losses are measured at 77 K for different Bi2223/Ag composite tapes under different room temperature stress/strain. The strain dependence of the critical currents and AC losses of Bi2223/Ag composite superconducting tapes are studied. A comparison is given for the measured results and the values calculated from the formulae developed from the Norris formula and critical current-strain relationship.

Research on Stability of

HTS materials can be used to develop novel permanent magnet (PM) motor. Based on the experimental and theoretical investigations, it was observed that the multi-impulse magnetization strategy should be selected for the constraints such as the temperature distributions and mechanical strength of the motor. The asymmetrical field distribution of HTS would induce torque ripples and unbalanced force. Proper cares have to be taken to avoid irreversible demagnetization. Resin impregnation and enclosing the rotor in a can/sleeve may provide the rotor enough mechanical strength to enable its high speed applications.

{\rm MgB}_{2}

Melt-textured high-T/sub c/ bulk superconductors can trap a strong magnetic field over 1 T at 77 K and reaches 10.1 T at 42 K. It is of great promise as a powerful magnet superior to conventional permanent magnets. Based on some potential application considerations, we emphasize to discuss its physical phenomena and relevant technical issues systematically in the paper, such as magnetization, the magnetic stability and mechanical effect, etc. In addition, a demo dipole motor will be shown as the first step of our present work aiming in finding out any possible novel ways to improve the traditional rotating machine by using high-T/sub c/ bulk superconductors.

Superconducting Magnet for MRI

In the application of high temperature superconductors, the superconducting tapes are often exposed to magnetic fields with different orientations. Thus AC losses in such cases depend not only on the magnitude of the external magnetic field, but also on its orientation with respect to the tape surface. In this paper, AC transport losses of a BSCCO/Ag tape were measured at 77 K in 48 mT, 80 mT and 120 mT DC magnetic fields, respectively. The angle between the direction of the magnetic field and the wide side of the tape varied from 0 to 90 degrees with a step of 10 degrees. Using the theoretical model we had proposed for the angular dependence of critical current, we developed a theoretical model to describe the angular dependence of AC transport losses by modifying Norris formula. The comparison between the theoretical values and the measured data were presented and discussed.

Critical current and AC loss of Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10//Ag tapes subjected to tensile stress

In this paper, the effect of viscous flux flow velocity (υ0) on the radial and hoop stresses in a type-II bulk superconductor shaped as a long circular cylinder is discussed for two magnetization processes: the decreasing field after zero-field cooling (ZFC) and field cooling (FC). With increasing υ0/R, i.e. υ0, as R is the radius of the cylindrical superconductor, the radial and hoop stresses increase and the remagnetization region is reduced. With different values of υ0/R, the maximum radial stress is equal to or greater than the maximum hoop stress for the ZFC case, and the maximum radial stress is equal to the maximum hoop stress for the FC case.