The numbers that matter
Critical current density (Jc)
How much current a superconductor carries per unit cross-section before it stops superconducting. A high transition temperature with a low critical current is not a conductor anybody can build with.
Why critical current density matters
It decides how much conductor a given current needs, and with it the mass, the cost and the size of the finished magnet.
Where critical current density comes up
Critical current density in a real conductor
- NbTiA ductile niobium-titanium alloy, and the only superconductor that can be drawn into wire on machinery a copper mill would recognize.
- Bi-2212The one high-temperature superconductor that can be made as a round, isotropic wire, and the reason it exists inside the strongest research magnets in the world.
- NbNA thin film with a high transition temperature for its class and a very short recovery time, which is what a single-photon detector is actually built around.
Related to critical current density
SuperMatics is a platform infrastructure company for superconducting devices: software that finds the material and the process, lab work that makes and measures it, and pilot manufacturing with industrial partners.If you have a device and a constraint it has to meet, tell us about it.