Electrical properties of cold-pressing welded NbTi persistent joints

• The cold-pressing welding method is employed to fabricate persistent joints.
• Performances of the joints have no apparent relevance to the mechanical pressure in a wide range of 4–20 MPa.
• Current decay ratio due to flux creep has obvious relevance to the mechanical pressure.
• Microstructures of persistent joints were observed with scanning electron microscope.
• Two different types of flux movement in joint loops have been observed and explained.

The cold-pressing welding method is employed to fabricate persistent joints between NbTi multifilamentary conductors, and a series of persistent joints are thus made at different mechanical pressures. The electrical properties of these persistent joints are tested by a joint resistance measurement device based on the current decay measurement method. Test results show that the cold-pressing welding method is reliable and applicable to NMR and MRI applications. Experiment results also shows that the joint resistances and current-carrying capacities of the joints seem to have no apparent relevance to the mechanical pressure in a wide range of 4–20 MPa, but the current decay ratio due to flux creep has obvious relevance to the mechanical pressure. Further research is needed to advance this joint manufacturing technology. Besides, measured current increase under 1 T background magnetic field is observed and explained, which has a reference meaning for testing persistent joint resistances.