Crémillieux, Y., et al., A Super-Wide Bore DNP System for Multiple Sample Polarization: Cryogenic Performance and Polarization at Low Temperature. Appl. Magn. Reson.: p. 1-14.
http://dx.doi.org/10.1007/s00723-012-0354-5
The volume of polarized sample and the delay required between successive polarizations of samples represent serious constraints for dynamic nuclear polarization (DNP) applications. With these limitations in mind, a DNP polarizer, based on a super-wide bore (150-mm diameter) vertical magnet operating at 3.35 T, was designed. The working diameter for loading/unloading samples is equal to 46 mm and the microwave cavity can accommodate up to three samples. The cryostat can be cooled to 4.2 K in typically 2 h and filled with liquid helium in 1 h. Once filled with liquid helium, the cryostat hold time is on the order of 4 h and a minimum temperature of 1.19 K can be reached. In situ polarization levels at low temperature were measured between 5 and 10 % in single and multiple samples of 13 C-labeled urea and glycine.