A compact X-Band resonator for DNP-enhanced Fast-Field-Cycling NMR

A new probehead was developed enabling Dynamic Nuclear Polarization (DNP)-enhanced Fast-Field Cycling relaxometry at 340 mT polarization field strength. It is based on a dielectric cavity resonator operating in the TM110 mode at 9.5 GHz, which is suitable for both transverse and axial magnet geometries with a bore access of at least 20 mm. The probehead includes a planar radio frequency coil for NMR detection and is compatible with standard 3 mm NMR tubes. The resonator was assessed in terms of the microwave conversion factor and microwave-induced sample heating effects. Due to the compact size of the cavity, appreciable microwave magnetic field strengths were observed even with only moderate quality factors. Exemplary DNP experiments at 9.5 GHz and 2.0 GHz microwave frequency are compared for three different viscous samples, demonstrating the advantage of DNP at 9.5 GHz for such systems. This new probehead enables new applications of DNP-enhanced Fast-Field-Cycling relaxometry of viscous and solid systems. (C) 2016 Elsevier Inc. All rights reserved.