4.5 Tesla superconducting miniature magnet in liquid nitrogen

We demonstrate a 4.5 Tesla high-temperature superconductor magnet (HTS) operating in liquid nitrogen (LN₂) at 77 K as a proof-of-concept platform for compact high-field generation. While cryocooler-based HTS magnets and liquid helium cooled magnets are already established, LN₂ cooled magnets offer simpler and potentially lower infrastructure cooling approach compared to cryofree or liquid helium. Additionally, liquid helium (LHe) remains scarce, expensive and challenging to handle. With HTS technology that allows for high magnetic fields even with LN₂ cooling, we developed a double-pancake coil magnet to assess its performance. The magnet was constructed with 2 × 200 m, 10 mm wide HTS tape, not exceeding the width of a pencil length. Each single pancake (1 × 200 m) coil was powered individually, generating a magnetic field strength of 3 Tesla. Stacking the pancake coils yields a double-pancake magnet that reaches a maximum field of 4.5 Tesla when operated in parallel. These results were obtained with pancake coils that had previously been quenched in LHe, indicating the robustness of our manufacturing and operation approach. The present work demonstrates the feasibility of LN₂-cooled HTS magnets for NMR-relevant high-field applications and provides a basis for future optimization of geometry, field homogeneity, and operating temperature. Ultimately reaching sufficiently high magnetic fields and homogenity for nuclear magnetic resonance spectroscopy (NMR) operated solely in LN₂.