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October 26, 2009

Magnifye Makes Powerful 17 Tesla Superconducting Magnets That Take up 2 Million times Less Space and Are Cheaper to Charge


Magnifye, a Cambridge University spin-out, would increase the power density of magnets used to produce energy in electric motors. The magnets, which are 10 times stronger than conventional magnets, are so powerful that a 1 inch sample could potentially support the weight of a seven-ton truck. (H/T Talkpolywell)

* Stronger magnets that are 7-17 tesla instead of just 2-3 tesla for industrial and medical applications
* 2 million times less volume. Instead of the volume of a phone booth they are the size of a hockey puck or less.
* Cheaper to charge using a new process. A thermal engines sends magnetizing waves that build up the magnetic charge
* Magnifye is developing the technology to produce the strongest permanent magnets in the world.
* Research paper links are at the bottom of this article

Magnifye has developed a heat engine which converts thermal energy into currents of millions of amps. The thermal energy is used to create a series of magnetic waves which progressively magnetise the superconductor much in the same way a nail can be magnetised by stroking it over a magnet.

As long as the superconductor stays cold, the currents will flow uninterrupted, providing powerful, stable, shapeable magnetic fields for a wide range of applications. These powerful magnets can be small enough to fit in the palm of the hand and large enough to power a train or a cruise liner.


It normally takes roughly a couple of cubic metres of solenoid to produce a magnetic strength of 7 Tesla. Up to 9.4 Tesla is deemed safe for humans. In May, 2009, a Magnifye superconducting magnet could produce 7 Tesla in an area that is 1 inch across and 0.5 inch deep.

EETimes Europe reports:

The work at the engineering department of Cambridge university was carried out using standard bulk magnets made from yttrium barium copper oxide (YBCO), a superconducting ceramic material that is readily available from many manufacturers worldwide. The superconducting properties only come into effect as the magnets are chilled to 93K (minus 180 degrees Celsius) using liquid nitrogen, unleashing the magnets' capability to maintain very high current loops and hence very strong magnetic fields.

Currently, all commercial magnetization processes require the presence of a magnetic field of equal or greater magnitude than the one to be induced into the superconducting material. This problem in itself translates into huge and expensively crafted electromagnetic coil assemblies that limit very much the use of superconducting permanent magnets in industrial applications.

The external magnetic field applied also turns out to be a limiting factor, when depending on geometries, the actual superconducting material would have the potential to trap a stronger magnetic field. The method that Dr Coombs has developed to magnetize the YBCO bulk eliminates these limitations and yields magnetic fields about ten times stronger than what alternative processes are capable of. The resulting magnets range in strength from 2 Tesla up to around 17 Tesla and are only limited by their intrinsic superconducting properties.

The thermal energy as it is dispensed creates a series of magnetic waves which gradually magnetize the superconductor at a fraction of the costs involved in conventional approaches. It is in effect a thermally actuated superconducting flux pump that builds up the magnetic field incrementally.

This enables Magnifye to convert thermal energy into currents of millions of amperes that run without electrical resistance in the superconducting material. Then as long as the superconductor stays cold, these currents flow forever, providing powerful and stable magnetic fields.

“This is heavy physics” warns Dr Coombs as he goes into the details of his research, though the implications for our everyday lives are much more obvious. Because the new magnetization method can be implemented in-situ, it could bring to life a new generation of superconducting motors or generators.


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RESEARCH PAPERS
A thermally actuated superconducting flux pump from Physica C (7 page pdf)

A novel heat engine for magnetizing superconductors published in SUPERCONDUCTOR SCIENCE AND TECHNOLOGY (7 page pdf)

The potential of bulk melt-processed YBCO single domains to trap significant magnetic fields (Tomita and Murakami 2003 Nature 421 517–20; Fuchs et al 2000 Appl. Phys. Lett. 76 2107–9) at cryogenic temperatures makes them particularly attractive for a variety of engineering applications including superconducting magnets, magnetic bearings and motors (Coombs et al 1999 IEEE Trans. Appl. Supercond. 9 968–71; Coombs et al 2005 IEEE Trans. Appl. Supercond. 15 2312–5). It has already been shown that large fields can be obtained in single domain samples at 77 K. A range of possible applications exist in the design of high power density electric motors (Jiang et al 2006 Supercond. Sci. Technol. 19 1164–8). Before such devices can be created a major problem needs to be overcome. Even though all of these devices use a superconductor in the role of a permanent magnet and even though the superconductor can trap potentially huge magnetic fields (greater than 10 T) the problem is how to induce the magnetic fields. There are four possible known methods: (1) cooling in field; (2) zero field cooling, followed by slowly applied field; (3) pulse magnetization; (4) flux pumping. Any of these methods could be used to magnetize the superconductor and this may be done either in situ or ex situ.
Ideally the superconductors are magnetized in situ. There are several reasons for this: first, if the superconductors should become demagnetized through (i) flux creep, (ii) repeatedly applied perpendicular fields (Vanderbemden et al 2007 Phys. Rev. B 75 (17)) or (iii) by loss of cooling then they may be re-magnetized without the need to disassemble the machine; secondly, there are difficulties with handling very strongly magnetized material at cryogenic temperatures when assembling the machine; thirdly, ex situ methods would require the machine to be assembled both cold and pre-magnetized and would offer significant design difficulties. Until room temperature superconductors can be prepared, the most efficient design of machine will therefore be one in which an in situ magnetizing fixture is included.
The first three methods all require a solenoid which can be switched on and off. In the first method an applied magnetic field is required equal to the required magnetic field, whilst the second and third approaches require fields at least two times greater. The final method, however, offers significant advantages since it achieves the final required field by repeated applications of a small field and can utilize a permanent magnet (Coombs 2007 British Patent GB2431519 granted 2007-09-26). If we wish to pulse a field using, say, a 10 T magnet to magnetize a 30 mm × 10 mm sample then we can work out how big the solenoid needs to be. If it were possible to wind an appropriate coil using YBCO tape then, assuming an Ic of 70 A and a thickness of 100 μm, we would have 100 turns and 7000 A turns. This would produce a B field of approximately 7000/(20 × 10^−3) × 4π × 10^−7 = 0.4 T. To produce 10 T would require pulsing to 1400 A! An alternative calculation would be to assume a Jc of say 5 × 108Am−1 and a coil 1 cm2 in cross section. The field would then be 5 × 10^8 × 10^−2 × (2 × 4π × 10^−7) = 10 T. Clearly if the magnetization fixture is not to occupy more room than the puck itself then a very high activation current would be required and either constraint makes in situ magnetization a very difficult proposition.
What is required for in situ magnetization is a magnetization method in which a relatively small field of the order of millitesla repeatedly applied is used to magnetize the superconductor. This paper describes a novel method for achieving this.


Superconductors: The Next Generation of Permanent Magnets published in IEEE Transactions on Applied Superconductivity (5 page pdf)

Magnets made from bulk YBCO are as small and as compact as the rare earth magnets but potentially have magnetic flux densities orders of magnitude greater than those of the rare earths. In this paper a simple technique is proposed for magnetising the superconductors. This technique involves repeatedly applying a small magnetic field which gets trapped in the superconductor and thus builds up and up. Thus a very small magnetic field such as one available from a rare earth magnet can be used to create a very large magnetic field. This technique which is applied using no moving parts is implemented by generating a travelling magnetic wave which moves across the superconductor. As it travels across the superconductor it trails flux lines behind it which get caught inside the superconductor. With each successive wave more flux lines get caught and the field builds up and up. The wave could be generated in many different ways but the preferred way is simply to heat a material whose permeability changes with temperature at its edge. As the heat travels across the material so the permeability changes and a magnetic wave is generated. It is in effect the first novel heat pump in a very long time and one which will enable the enormous potential available from these unique and highly versatile superconducting magnets to be fully realised. Within this paper we present results showing the superconductor being progressively magnetised by sequentially applied “heat” pulses. We also demonstrate that the sign of the magnetisation is reversed if “cold” pulses are applied instead of heat pulses. These experimental results are supported by modelling.

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