Cylindrical spinner and speed controller for magic angle spinning nuclear magnetic resonance

Abstract

A new design for a cylindrical spinner suitable for magic angle spinning nuclear magnetic resonance (NMR) is described. The rotor has a large sample volume (0.66 cm³) and is capable of spinning speeds from 500 Hz to 5 kHz at drive gas pressures below 50 lb/in.². The rotor is completely supported by gas bearings. Axial positioning is provided by the rotor’s T shape, leaving the bottom surface available for a photoelectric tachometer. The coil is wrapped on a form machined into the outer surface of the stator, producing a high filling factor. Also described is an instrument which controls the spinning speed of such a rotor to ±0.6 Hz around a set speed in the range of 3–4 kHz. The rotor’s speed is determined by means of a photoelectric tachometer. The instrument then compares this measured speed to the desired value and adjusts the gas flow to the rotor to correct any difference.