Riken and Chiba University developed a new method to form an insulating part and reduced the thickness of the insulating part of a next-generation high-temperature superconducting wire that uses a rare earth material by more than 90% to 4μm.
Riken is a Japan-based independent administrative institution. The thinner insulating part increases the current density of a superconducting coil, enabling to reduce the size of the coil. Before the latest development, the insulating part was as thick as the current-carrying part of the wire, lowing the current density of the coil.
The width and thickness of the next-generation high-temperature superconducting wire are 4-5mm and 100-150μm, respectively, and it looks like a tape. To use the wire as a superconducting coil, it is necessary to cover the wire with an insulating material.
The newly-developed method for forming the insulating part is based on the "polyimide electrodeposition method," which attaches positively-charged polyimide particles to a negatively-charged wire. It enables to form a uniform, ultra-thin polyimide insulating film not only on the flat area of the tape-like wire but also on its corners.
This method not only realizes a thinner insulating part but also enables to easily form an insulating part with a smaller number of processes because there is no need to worry about the break or ununiformity of tape, compared with conventional insulation methods using insulating polymer tapes. In addition, it can be easily applied to several kilometer-long wires.
The insulation ratio of the new superconducting wire's cross-section area (including the insulating part) is 10% or lower (it was 50% or higher in the past). Because the current density of the superconducting coil is doubled, it becomes possible to reduce the volume of a superconducting coil by 80% or more (in the case of a superconducting coil that has an inner diameter of 10cm and generates a 10T magnetic field in the center).