If we define ultra-high field (UHF) magnets as those that provide fields more intense than the 23.4 T available from low temperature superconductors, then we see tremendous progress being made worldwide in recent years. An absolute revolution is underway in superconducting magnets with the high temperature superconductors (HTS) finally finding their way into condensed matter (Sendai 25 T, Tallahassee 32 T) and NMR (Bruker 28.2 T) magnets in routine operation. Newer applications such as axion detection are also being enabled by this revolution (Daejeon 25 T, 10 cm). Projects are underway for a number of 30 T-class condensed matter magnets around the world as well as a few organizations pursuing 30.5 T NMR and 40 T for condensed matter.
A number of technologies are being pursued. A Bi-2223 coil has been put into service at 25 T while insulated REBCO has served users at 32 T. A test coil using no-insulation REBCO made 14 T in a 31 T background (45 T total) while dramatic improvements in Bi-2212 show great potential as well. The record field from a superconducting magnet rose from 23.5 T to 24 T to 32 T in less than one year. The previous 8 T increase required >40 years! The technology is evolving at an unprecedented rate! At the same time, costs show great promise of dropping which may enable this extraordinary technology to become fairly widespread.
HTS magnet technology is also creating a new commercial industry: magnetic confinement for fusion. This field has been dominated by national governments for decades, but the HTS materials allow more compact designs at higher field to be developed which show potential to reduce the cost of a tokamak. While these magnets are not "UHF" large-scale financing is being organized and technical improvements in this community is impacting the UHF community.
While differetn groups and applications use different UHF magnet technologies, they all still share central challenges such as how to manage intense Lorentz forces as well as the required energy and power. The state of the art and challenges associated with further development of a variety of ultra-high field magnet systems is presented.
Keywords: High field magnet, 2G HTS magnet, large-scale superconducting system