Superconductivity
A superconductor exists within a BJT critical surface bounded by the supercondutor’s critical magnetic field (Bcrit), critical current density (Jcrit) and critical temperature (Tcrit). Within this space, the superconductor exhibits essentially zero resistance to current flow.
Superconductivity was discovered in 1911 by the Dutch physicist, Heike Kammerlingh Onnes when he was able to liquefy helium by cooling it to 4 Kelvin, or -452 deg F. This enabled him to cool other materials close to absolute zero and investigate their material properties. Commercial superconductors come in two types, low temperature (LTS) and high temperature (HTS). The temperature that defines each is the level to which the conductors need to be cooled in order to become “superconducting”. Low temperature superconductors were first available commercially in the 1960’s and have critical temperatures below 18K. LTS materials typically require expensive and increasingly scarce LHe as a coolant, operating at 4.2K. Current applications for LTS are in magnetic resonance imaging (MRI) magnets and high field magnets used in research such as NMR spectroscopy and high energy physics particle accelerators. SuperPower’s parent company, Furukawa Electric has a long history in the production of LTS for these and other applications.
The discovery in Switzerland of ceramic based high temperature superconductors (HTS) in 1986 opened the possibility of applying superconductivity to a broader range of applications. The “high” in HTS refers to the ability to achieve the superconducting state with critical temperatures exceeding 90K. This allowed cooling at temperatures attainable using inexpensive liquid nitrogen. SuperPower has developed the capability to produce long lengths of tape based on these ceramic HTS materials with these higher transition temperatures, called high-temperature superconductors. In addition to the higher transition temperature, the HTS materials exhibit very high critical magnetic fields and critical current densities, particularly when cooled to lower temperatures. HTS offers performance advantages and operating space that do not exist with LTS.