In contrast, the most powerful commercial SC magnets currently available can achieve a stable field of up to At first glance, SC magnets might seem much more complicated than electromagnets, especially with the requirement for low temperatures to keep the magnet solenoid in its superconducting state. However, they have several advantages over their permanent or electromagnetic counterparts. First, SC technology allows users to produce extremely high magnetic fields without the many kilowatt, or even megawatt, power supplies needed for electromagnets.
Second, SC magnets can also generate a far higher field than permanent magnets, which are limited to 2 T. SC magnets are currently capable of up to This can be extended to around 45 T with the addition of a resistive or electro- magnet, but obviously this removes some of the advantages, as a permanent electricity supply is now needed. Although electromagnets are capable of generating fields of up to 35 T, the power consumption required for this would be considerable.
In addition, an SC magnet field can be kept extremely stable with a very low drift rate and very high homogeneity, features that are essential for applications such as NMR spectroscopy and fourier transform mass spectrometry FT-MS.
Third, SC magnets have a very small footprint in comparison to electromagnets typically the coils of a resistive 1 T magnet are 10 times larger than a SC 10 T magnet , and the space needed is further reduced because they do not require water cooling for the power supply or solenoid.
However, a cryogen such as liquid helium is needed to cool the magnet to below its superconducting critical temperature Tc and liquid helium is relatively expensive in some parts of the world. For the superconductor niobium titanium, Tc is 9 K; above this the material becomes resistive. SC magnets are used the world over in a huge variety of applications. In healthcare, magnetic resonance imaging, which is almost universally employed for clinical diagnosis, is dependent upon high quality SC magnets.
Molecular biology also benefits from the SC magnets found at the heart of high-resolution NMR techniques that are essential in drug discovery and development. SC magnets have been continually evolving over the last 40 years to become larger and more powerful, culminating recently in the commercial availability of MHz NMR magnets.
So why have people continued to demand bigger and better magnets, and what benefits do they bring? Several essential features of NMR spectrometer performance are controlled by the size and quality of the SC magnet found at the centre of the instrument. This leads to higher information content, allowing the detection and characterisation of smaller amounts of material and more complex molecules — proteins of up to kilo-Daltons have been successfully analysed at MHz.
However, in order to achieve this greater detail, the SC magnet needs to provide a magnetic field of very high homogeneity and stability. The homogeneity has to be better than 1 part in ten billion over the sample volume typically 5 mm diameter by 25 mm long. Many of these factors become more difficult to maintain with magnets of increasing size and strength. In fact, even the increase in magnetic field strength from to MHz required several critical parts of the magnet to be redesigned.
First, a conductor has to be chosen that can provide a stable field at MHz, since the field drift rate has to be kept to 1 in for high-resolution NMR experiments. When you run an electric current through a wire, it creates a magnetic field; the strength of the magnetic field is proportional to the amount of electric current.
Magnets created this way are called electromagnets. By controlling the amount of current, we can make electromagnets of any strength we want. Given the connection between electrical current and magnetic field strength, it is clear that we need huge currents in our accelerator magnets. To accomplish this, we use superconductors, materials that lose their resistance to electric current when they are cooled enough.
Given the central role of magnets in modern accelerators, scientists and engineers at Fermilab and CERN are constantly working to make even stronger ones. To use all functions of this page, please activate cookies in your browser. Login Register. Additional recommended knowledge. Topics A-Z.
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To use all the functions on Chemie. DE please activate JavaScript. For their discovery, these scientists received the Nobel Prize in Physics in Following the discovery of superconductivity in mercury, the phenomenon was also observed in other materials at very low temperatures. The materials included several metals and an alloy of niobium and titanium that could easily be made into wire.
Wires led to a new challenge for superconductor research. Technologically, wires opened whole new uses for superconductors, including wound coils to create powerful magnets.
In the s, scientists used superconducting magnets to generate the high magnetic fields needed for the development of magnetic resonance imaging MRI machines. More recently, scientists introduced superconducting magnets to guide electron beams in synchrotrons and accelerators at scientific user facilities. In , scientists discovered a new class of copper-oxide materials that exhibited superconductivity, but at much higher temperatures than the metals and metal alloys from earlier in the century.
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