MgB₂

MgB₂ in numbers

Transition temperature

39 K

Made as

wire

Nitrogen line

Below 77 K

Why engineers choose MgB₂

MgB2 is the conductor that takes liquid helium out of the room. Its transition temperature is high enough to run a magnet on a closed-cycle cryocooler with no bath, which means no cryogen deliveries, no recovery plant, and no quench that vents into a hospital corridor. That is not a performance argument, it is an operating-cost and siting argument, and it is why the first helium-free MRI scanners are wound from it. The material is also magnesium and boron, with no rare earth and no silver in it, so the raw ingredients are not the reason it is expensive.

Where MgB₂ stops

The temperature headroom does not convert into field headroom. Run it warm and the current it will carry under field falls away, so the operating point that makes the cryogenics easy is the one where the magnet is weakest. Every design using MgB2 is a negotiation between those two facts.

• Current under field

  Irreversibility under 8 T at 20 K, so the temperature headroom buys nothing in field.