Highest Magnetic Field

Strong magnetic fields are required in many fields. They are used, for example, in medicine for magnetic resonance imaging (MRI), in pharmacy for nuclear magnetic resonance (NMR), and for particle accelerators such as the Large Hadron Collider (LHC). For almost two decades, 45 T has been the highest achievable direct-current (d.c.) magnetic field. To generate such a field a 31-MW, 33.6-T resistive magnet inside 11.4-T low-temperature superconductor coils is required. Such high-power resistive magnets are available in only a few facilities worldwide. Superconducting magnets have lower power requirements and are widespread.

David C. Larbalestier, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA, and FAMU-FSU College of Engineering, Tallahassee, FL, USA, and colleagues have built an electromagnet that is stronger, smaller, and more versatile than ever before. The high-temperature superconductor coil generates a magnetic field of 14.4 T inside a 31.1-T resistive background magnet to obtain a d.c. magnetic field of 45.5 T—the highest field achieved so far.

The heart of the magnet is a 43 µm thin, multi-layer tape, the so-called REBCO tape. It consists of a carrier layer on which a layer of a cuprate is applied. The cuprate consists of yttrium, gadolinium, and barium (REBa₂Cu₃O_x, where RE = Y, Gd). REBCO can carry more than twice as much current as a same-sized section of a niobium-based superconductor. On top of the REBCO tape are a silver layer and a copper stabilizer. This tape is tightly wound around a copper core.

The coil is highly compact and capable of operating at very high winding current densities because the magnet is wound without insulation. This allows rapid and safe quenching from the superconducting to the normal state. The scientists placed this superconductor electromagnet in a helium-cooled tube. The tube was located inside a conventional electromagnet. The magnet is thus a hybrid in which the superconducting magnet is located inside the ohm magnet.

According to the researchers, this magnet shows a viable way to high-field copper oxide superconductor magnets.