A high-field air-cored magnet coil design for fast-field-cycling NMR

Abstract A mathematical formalism is described which allows the design of the most effective geometry for homogeneous, fast-switchable field-cycling magnets. The method minimizes the electric power needed to produce a flux density B subject to constraints on the homogeneity and effective volume. It was used to build a low-inductance 1.2 T coil for fast-field-cycling NMR experiments with protons at 50 MHz and with deuterons at 7.5 MHz. Driven by a 25 kW MOSFET switch the field turn-on and turn-off times can be adjusted to less than 0.4 ms. Data for a projected 2.4 T coil, which will extend the field-cycling range to Larmor frequencies of 100 and 15 MHz, respectively, are also given.