Russia, and Japan, and new ones are being constructed in South Korea, China, and India. All the fusion devices being used or being considered require very large superconducting magnets. The United States is now operating only one superconducting fusion device, known as the Levitated Dipole Experiment. However, it has had an extensive superconducting magnet development program under way since the 1970s. In the 1980s the extremely large superconducting mirror machine MFTF-B was started up at Lawrence Livermore National Laboratory, but it never went into full operation for reasons unrelated to magnet technology.
Fusion magnets come in many shapes and sizes, including solenoids, toroids, and helical coils. The devices presently in operation use Nb-Ti magnets, but newer machines will use Nb3Sn magnets. The largest project now being planned is the International Thermonuclear Experimental Reactor (ITER), which will be a collaboration between the United States, Europe, Russia, Japan, China, South Korea, and India. The device will cost more than $5 billion and is scheduled to be constructed over 8 years beginning in 2006. This machine will require the commercial production of about 500 tons of high-quality Nb3Sn superconductor over a several-year period, a more than 10-fold increase in world production of Nb3Sn.
During the 1990s the parties involved in ITER made several large-scale prototype superconducting magnets. The largest of these was the Central Solenoid Model Coil, built jointly by the United States and Japan. Its coil has an inner diameter of 1.6 m, an operating current of 46,000 A, a peak field of 13 T, and a stored energy of 640 MJ. It can be operated as a DC magnet or ramped from zero field to 13 T in 8 s without quenching.
These examples suggest the broad utility and critical importance of high-field magnet science and technology in fields beyond condensed-matter physics, materials science, and magnetic resonance. Although the scale of application for high-field magnets in a high-energy particle accelerator is vastly different than that associated with the study of correlated-electron systems, both communities drive—and benefit from—general advances in high-field magnet technology. It is important to note that these disparate communities of users have not traditionally collaborated on magnet technology. Indeed, the recent convergence of the particle physics and fusion science magnet efforts was precipitated more by their shared source of funding (DOE’s Office of Science) than by any overlap of ongoing research efforts. It is nevertheless the case that advances in magnet design, construction, and performance made by one community can significantly benefit other communities.