An ultra-thin polyimide insulation coating on REBCO conductors by electrodeposition produces a maximum overall current density for REBCO coils

•We developed a 4 μm-thick ultra-thin polyimide coating on REBCO conductors.•The developed coating improves the fraction of conductor in the coil to 90%.•The coating dramatically increases the overall current density of REBCO coils.

One apparent shortcoming of REBCO conductor coils is an extremely low fraction of conductor in the coil winding, as the REBCO conductor is as thin as 100–150 μm, comparable to the insulation thickness. If we wish to achieve high overall current densities for REBCO coils, the insulation thickness on REBCO conductor must be substantially reduced. Therefore, we have developed a 4 μm thick ultra-thin polyimide insulation coating by electro-deposition, which is 10-fold-thinner than conventional insulations on REBCO conductors. The fraction of REBCO conductor in the coil winding manufactured by this novel conductor becomes as high as 90%, which is comparable to that for a low temperature superconducting coil winding manufactured from Formvar-coated NbTi conductor. Thus, one important shortcoming of REBCO coils is satisfactorily overcome by using ultra-thin polyimide coated conductors, making possible a dramatic increase in the overall current density of such coils.