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Researchers at Los Alamos National Laboratory have found a way to manufacture low cost superconducting wire that may make magnetic resonance imaging (MRI) machines affordable for most doctor’s surgeries.
Back in 2001, it was discovered that magnesium diboride (MgB2) exhibited superconducting behaviour. This caused great excitement in the field as magnesium diboride is a much simpler material than many of the mixed oxides superconductors that have been produced that become superconducting at higher temperatures. However, its biggest advantage is that it is much cheaper to produce then those materials.
Current MRI machines use niobium alloy wires which require liquid helium to cool them to temperatures low enough for them to be superconducting. Magnesium diboride can be cooled with liquid neon, which is much more affordable then liquid helium and magnesium diboride is also cheaper than the niobium alloys used in MRI machines.
However, for magnesium diboride to be useful in MRI machines, it needs to be available in wire form, which posed the next problem for researchers, otherwise it would be no more useful then the exotic mixed oxides that researchers have produced in laboratories.
The researchers used the so-called powder-in-tube method to produce the magnesium diboride superconducting wires. This involved encasing the magnesium diboride powder in a thin iron tube.
This idea was not initially very successful as the system was too porous to achieve critical current density. To overcome this problem they produced wires and formed them into coils which they hot isostatically pressed (HIP’ed). This process brought the superconducting powders into intimate contact, reducing porosity and increasing current carrying capacity by 45% compared to magnesium diboride wires produced using traditional annealing methods.
It was also found that the hot isostatic pressing operation induced more structural defects that are beneficial in increasing the current carrying capacity, with higher current carrying capacity equating to thinner wires.
They believe that they can reduce the cost of the superconducting wire used in MRI machines from $3-10 per kiloampere of current per metre of wire to $1-2. Due to the amount of wire required for an MRI machine, this makes a significant difference to the cost of the machine, potentially making MRI machines affordable for most doctors and even veterinarians.
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