Superconducting magnet

Superconducting magnets are electromagnets partially build from superconducting materials and therefore reach much higher magnetic field intensity.

Construction

Composition

Coil windings

The coil windings of superconducting magnet are made of wires of a type 2 superconductor (e.g.niobium-titanium).

Coil

The coil itself is made of tiny filaments (about 20 micrometers thick) of a type 2 superconductor, coated with copper. The copper coating is needed for adding mechanical strength to the fiber, and in case the temperature rises above T_c or I_c at which point superconductivity is lost. These filaments need to be this small because in this type of superconductor, the current only flows skindeep.

Cooling

Liquid helium is used as coolant since this is the only substance which is liquid at the extreme temperatures of superconductors.

Materials

The superconducting portions of most such magnets are composed of titanium-niobium. This material has critical temperature of 10 kelvin and remains in this state till about 15 tesla. More expensive magnets can be made of niobium-tin (Ni₃Sn). These have a T_c of 18 kelvin. When operating at 10 kelvin they are able for withstanding a much higher magnetic field intensity. Unfortunately, it is far more difficult to make the required filaments from this material. This is why sometimes a combination of Ni₃Sn for the high energy parts and Ni₃Ti for the lower energy parts is used.

Use

Superconducting magnets can reach a much higher magnetic field intensity than normal magnets and they can hold this field for a long time. This is particullary needed in Particle accelerators and Nuclear magnetic resonance. For economic reasons these magnets are also used when a field of more than 1 tesla must be maintained for a long time.