Persistent joint development for high field NMR

A large NMR magnet links several Nb/sub 3/Sn and NbTi coils in series. The circuit can contain as many as fifty superconducting joints. The persistence requirements of NMR impose limits on the total circuit resistance. Ideally the magnets total resistance is determined by the field integrated n-value loss in the coils and the resistive sum from the joints. Designing sufficient margin into each coil's conductor can mitigate the decay resulting from n-value loss. Joint losses are the remaining aspect of the design that must be controlled for NMR, joint losses can be conservatively estimated from the upper limit in the resistance measurement sensitivity used during process development. An NMR magnet requires several joint configurations to allow fabrication and assembly of the circuit. There are joints between Nb/sub 3/Sn conductors inside coils, joints between NbTi conductors, and persistent joints between NbTi and Nb/sub 3/Sn conductors. A range of processing methods is required given the complexity of the assembly. This paper presents a review of this subject concerning the available methods for joint fabrication, a measurement method for process development, and supporting measurement results.