Lectures on Superconductivity: Applications

An air-cooled copper electromagnet cannot be used for current densities greater than 20 A mm^-2. A Bitter electromagnet uses alternating copper and insulating plates with water cooling channels to achieve high magnetic fields, but very large power generators and high water flow rates are required.

Pulsed magnets can achieve 50 T, but only for a short time (tens of milliseconds). A large amount of energy must be provided rapidly, for which banks of capacitors are usually used. 300 T can even be reached, but only with a destructive design in which the magnet coil is disposable, and for pulses in the microsecond range.

Practical electromagnets for constant high magnetic fields can only be produced using superconductors. Superconducting magnets based on NbTi and Nb₃Sn are required for many important applications including MRI, magnetic separation and particle accelerators.