Calculation of a magnetic force acting on small superconducting celestial bodies

Funder: CERNAbstractRecent discoveries of superconducting phases in the samples of meteorites suggest the possibility of a natural occurrence of superconducting state in space. Superconductors are known to exhibit interesting behaviours when subjected to external magnetic fields, such as levitation. Similar force may act on a superconducting bit in space. The goal of this paper is to quantify this force and assess its effects. Several scenarios in which a superconducting bit can be produced and interact with a magnetic field in space are suggested. The force acting on a superconductor in different conditions is calculated with numerical simulations. The dependence on a magnetic flux density, its gradient, and the geometry and the properties of the superconductor are found. The empirical formulas are derived and used to calculate a magnetic force. The resultant force is extremely weak in all analysed scenarios. It is found that its strength decreases rapidly with the distance from the source of the magnetic flux. Its effect on trajectory of the superconductor is almost negligible. Some possibilities of increasing its strength and the effects are considered.</jats:p

Superconducting Magnetic Heterostructured Components for Electric Motor Applications

Trapped flux magnets made by stacking high temperature superconducting tape portray an easy assembly with already available materials, high mechanical resistance, provided by the substrate and improved thermal stability, which enhances the trapped flux compared to bulks. This allowed reaching the world record of 17.7 T. The presented analysis expands previous work with wide superconducting tapes showing further pos-sible improvements in this kind of devices in order to be used as source of magnetic flux in electrical motors, substituting permanent magnets. The aims are to increase the trapped magnetic flux during magnetization and decrease the leakage flux at the edges of the magnet during the operation of the machine. This is expected to be achieved by either introducing new materials in-between the individual tapes, such as ferromagnetic layers, or modifying the composition of the substrate. The results of simulations using the H-formulation as well as experimental measurements are presented.EPSRC grant EP/P000738/

Experimental system for testing a superconducting motor at temperatures close to 15 K

Integrating superconducting elements in an electric motor can greatly increase its power density. By doing so, lighter and more powerful machines can be produced for applications such as aviation, wind turbines and marine propulsion. Superconducting tapes can be stacked and magnetised to produce powerful trapped-flux magnets. The experimental setup was designed to allow measurements in a low temperature environment, providing tightness for the rotating part. We report on the design and construction of the setup and results from its first operation. The temperatures achieved during the experimental measurements reached 15 K, close to the actual operational temperatures of a liquid hydrogen cooled motor. The application of hydrogen onboard an aircraft is highly advantageous due to the possibility of its application as both coolant and fuel. Examination of the operation of the trapped-flux magnets at such temperatures is crucial for the understanding of the behavior of fully superconducting motors for future applications

Effect of HTS stack sectioning on pulse magnetization efficiency in a motor

Abstract Stacks of HTS superconductors can be magnetized and used as a surface mounted magnet for electrical machines. Pulse field magnetization is considered as a practical method; however, the amplitude of the pulse can be limited in an electrical motor which results in an under-saturated stack with the superconducting currents penetrating only a part of it making the magnetization less efficient. A solution to this problem could be sectioning the stack along its width enabling effective penetration of the superconducting currents. In this paper we investigate the effect of sectioning of HTS surface mounted stacks on the efficiency of pulse magnetization method in trapping the flux using low pulsing field. It is shown that the sectioning of wide stacks into several narrower parts results in a higher trapped flux at low pulses. Experimental measurements are performed on a lab-scale motor to validate the theoretical analysis.</jats:p

Heat extraction from HTS tape stacks applied in a superconducting motor in different cooling conditions

Abstract The heat is generated inside the stack of superconducting tapes mounted on the surface of the electrical machine rotor during its operation and magnetization. Cooling of such stack presents challenges because of the layered structure of both tape, and stack. Moreover, the tapes should be electrically isolated to minimize the AC losses, that assumes gluing them, rather than soldering. The calculations consider a conductive heat dissipation also through the rotor iron. Results show that: liquid nitrogen provides an effective cooling; the temperature of the stack shows complex distribution patterns with the gaseous coolant. Additional preventive measures were analyzed to keep the stack operational in vacuum conditions.</jats:p

Trapped-flux magnets characterization for application in synchronous machines

Abstract Trapped-flux magnets comprising stacked superconducting tape constitute a promising development to increase the power density of electrical machines, whilst at the same time keeping the complexity required in their construction in manageable levels that allow their use in applications such as aircraft propulsion. However, the conditions in which superconducting stacks operate inside an electrical motor differ quite significantly from the materials characterization experiments commonly developed to model their behaviour. This work presents the results of studying the applicability of these devices as magnetic flux source in the rotor of synchronous machines considering the influence of whole magnetic circuit. Several aspects are assessed, such as flux harmonics, magnetization, losses and demagnetization. Analytical expressions, which provide limited accuracy but allow fast calculations, are used for this purpose. The results illustrate the different trade-offs that arise during the design of a synchronous electric motor using trapped-flux magnets.</jats:p

Effect of HTS stack sectioning on pulse magnetization efficiency in a motor

Abstract: Stacks of HTS superconductors can be magnetized and used as a surface mounted magnet for electrical machines. Pulse field magnetization is considered as a practical method; however, the amplitude of the pulse can be limited in an electrical motor which results in an under-saturated stack with the superconducting currents penetrating only a part of it making the magnetization less efficient. A solution to this problem could be sectioning the stack along its width enabling effective penetration of the superconducting currents. In this paper we investigate the effect of sectioning of HTS surface mounted stacks on the efficiency of pulse magnetization method in trapping the flux using low pulsing field. It is shown that the sectioning of wide stacks into several narrower parts results in a higher trapped flux at low pulses. Experimental measurements are performed on a lab-scale motor to validate the theoretical analysis

Magnetic flux in stacks of superconducting tapes of different architecture

Stacks of superconducting tapes nowadays have multiple applications and many new modifications are currently considered to enhance their beneficial properties. We have studied the field trapping in stacks of commercial superconducting tapes with different configurations. Experimental and numerical analyses were performed. The superconducting stacks were magnetized to act as powerful permanent magnets using pulsed field magnetization and field cooling at 77 K. The configurations include a basic stack made of layered tapes, a stack interlayered with ferromagnetic material, a sectioned stack made of thin tapes and a shielded basic stack. The present study shows that, in terms of total trapped flux, the basic stack performs best, closely followed by the shielded stack. No significant positive effect due to the presence of ferromagnetic layers was found in the studied configuration. The sectioned stack is the worst according to every analysed criterion. The possibility of application of the analysed modification is discussed