Superconducting Magnets Research for a Viable US Fusion Program Joseph V. Minervini1, Leslie Bromberg1, Peter J. Lee2, David C. Larbalestier2,

Magnet systems are the ultimate enabling technology for magnetic confinement fusion devices. Powerful magnetic fields are required for confinement of the plasma, and, depending on the magnetic configuration, dc and/or pulsed magnetic fields are required for plasma initiation, ohmic heating, inductive current drive, plasma shaping, equilibrium, and stability control. Almost all design concepts for power producing commercial fusion reactors rely on superconducting magnets for efficient and reliable production of these magnetic fields. Future superconducting magnets for fusion applications require improvements in materials and components to significantly enhance the feasibility and practicality of fusion reactors as an energy source.

An integrated program of advanced magnet R&D should be focused on developing alternative and innovative approaches that would lead to radical advances to substantially improve and accelerate the path to fusion reactor. A new opportunity that could significantly change the economic and technical status of superconducting magnets is now viable, namely the use of so-called High Temperature Superconductors (HTS) that have now been used for demonstration of superconducting fields > 30T in small bore solenoid geometries. Recent studies performed at MIT indicate that HTS magnets that make use of demountable magnets is becoming a feasible option for future devices. This could have massive impact on fusion reactor performance and on the ability to maintain the machine, and increase reliability and availability.

The state of the art in fusion superconducting magnet systems is ITER. The technology for ITER was developed in the 90’s, and although there are still some issues with the superconductor, the technology has been used successfully in model coils and in other smaller fusion experiments. In fact, all present and under-construction superconducting fusion systems (EAST, KSTAR, LHD PF coils, Wendelstein 7-X, ITER) use the Cable- in-Conduit-Conductor technology invented and developed in the US and in particular, at MIT. We also note with some despair, that the sole superconducting fusion physics device designed, built, and operated in the U.S., the Levitated Dipole Experiment (LDX), is supported only at the absolute minimum level by OFES.

Future superconducting magnets for fusion applications require improvements in materials and components to significantly enhance the feasibility and practicality of fusion reactors as an energy source. The fusion program should be developing magnet technologies that are specifically focused on enhancing physics performance through higher magnetic fields, and by substantially lowering the cost and increasing the availability of the magnets required in fusion power systems. The time for a revitalization of the U.S. fusion magnets programs is now, with a clear goal of improving post-ITER fusion reactor performance.

1 Massachusetts Institute of Technology 2 Florida State University