Structural materials for fusion magnets

Of major technical and cost impact to Magnetic Fusion Energy development are the materials for the magnet structure. Likened to gas pressure, the magnetic field lines try to expand the structure with equivalent pressures up to 1000 atm. Not only are large tensile forces produced, but significant bending forces may also be present. To withstand these forces in the restricted spaces available, materials of exceptional strength and toughness are required. In this regard, the low-temperature environment of superconducting magnets can be an advantage because many materials exhibit enhanced properties at reduced temperatures. Those materials and fabrication techniques that are attractive to fusion magnets are discussed and relative comparisons made. Considerations such as strength, toughness, and joining techniques are balanced agains recommended design criteria to reach an optimum design. Several examples of material selection are cited for large fusion magnets such as Baseball II, the Mirror Fusion Test Facility, the Toroidal Fusion Test Facility, and the Large Coil Project. (orig.)