Development of 'poly-layer' assembly technology for pulsed magnets

Historically the analysis of pulsed magnets has indicated that a coil assembly comprised by a layer-by-layer graded conductor coil is nearly optimum. Additionally the layer-to-layer winding transitions, associated with monolithic coil construction, are problematic and often the source of catastrophic failure in pulsed coils. FEA analysis of transition structures has confirmed the lessons of operational experience. Additionally the layer-to-layer winding transitions present an unacceptable risk a short circuit fault to the reinforcement structure. These attributes of monolithic coil construction have limited the fields where pulsed magnets can be operated to approximately 60 T. Several operational issues arise above this field: coil reliability degrades, and the time required to cool the magnet between shots is increased, since higher field monolithic coils require large amounts of distributed internal reinforcement to limit conductor strain. We are developing a new 'poly-layer' coil construction to address these engineering requirements. In this construction, each layer is wound separately on a forming mandrel, and then installed onto an assembly mandrel. Spool pieces are installed at each end to support the lead exits as they transition out of the windings. Each layer is joined in series with the next in joint structures that is constrained in the radial and circumferential directions, but free to move with the coil in the axial direction. Furthermore, the coil reinforcement is used to support the lead in the transition region between the windings and the joint. The new design represents a change in our manufacturing template that is intended to allow development of higher field coils. This paper report design details and the results from prototype testing.