A ferromagnetic shim insert for NMR magnets - Towards an integrated gyrotron for DNP-NMR spectroscopy

In recent years high-field Dynamic Nuclear Polarization (DNP) enhanced NMR spectroscopy has gained significant interest. In high-field DNP-NMR experiments (⩾400MHz ¹H NMR, ⩾9.4T) often a stand-alone gyrotron is used to generate high microwave/THz power to produce sufficiently high microwave induced B_1e fields at the position of the NMR sample. These devices typically require a second, stand-alone superconducting magnet to operate. Here we present the design and realization of a ferroshim insert, to create two iso-centers inside a commercially available wide-bore NMR magnet. This work is part of a larger project to integrate a gyrotron into NMR magnets, effectively eliminating the need for a second, stand-alone superconducting magnet.