40 Tesla miniature magnets

Ultrahigh magnetic fields enable substantial advancements across a wide range of scientific disciplines. Traditionally, steady fields above 40 tesla have been achievable only with large resistive magnets that consume megawatts of power. Here, we demonstrate peak fields of 38 and 42 tesla using two compact all-HTS magnets, composed of two and four pancake coils, respectively. These magnets achieve current densities of up to 2257 amps per square millimeter and feature an exceptionally small bore diameter of 3.1 millimeters. Furthermore, the magnet coils are small enough to fit in the palm of a hand and consume less than 1 watt of power. Such compact magnets are realized through specialized winding methods that enable seamless winding over the small diameter while preserving the current-carrying capacity of the HTS tape. Nuclear magnetic resonance (NMR) experiments were performed inside the 3-millimeter magnet bore to provide calibration points for Hall sensors. These results show the potential of compact all-HTS magnets to enable widely accessible high-field NMR and other applications.