Microstructural Aspects of Materials for Nondestructive Long-Pulse High-Field Magnets

The development of high-field magnets for pulsed-field applications is the subject of considerable research activity throughout the world. Induced field strengths in excess of 30 T can be produced only as pulses generated by the discharge of energy, e.g., from a capacitor bank into a resistive solenoid. A variety of electromagnetic design issues relate to the pulse duration, field strength, and volume of the coil; however, from the viewpoint of materials selection and coil design, there are two salient property requirements: (1) high electrical conductivity to minimize the temperature rise due to the flow of current in the coil, and (2) high mechanical strength to resist the Lorentz forces exerted during the pulse. Such forces can result in catastrophic failure, as illustrated in Figure 1, because the coil is, in essence, stressed in the manner of an internally pressured cylindrical vessel. At lower stresses, plastic distortion of the coil is observed.