Magnetic Field Homogeneity Optimization of the Giga-NMR Resistive Insert

The development of a Polyhelix resistive insert for high-resolution, solids NMR experiment is quite challenging. The targeted magnetic field homogeneity in a 1 cm diameter sphere volume is 1000 times less than what is observed with traditional Polyhelix magnets. The Polyhelix insert design is derived from our high field magnet optimization process to which we add some more constraints to enforce the field homogeneity. NMR measurements of the Giga-NMR resistive insert show that the achieved homogeneity is improved by an order of magnitude compared to High Field insert. Numerical investigations are carried out to analyze the observed inhomogeneity. Computations suggested a better configuration of the insert, which reduces the observed strong linear term. The expected behavior is confirmed experimentally