Apart from experiments at fixed magnetic fields strengths of 16.5 T (700 MHz) and 9.4 T (400 MHz), field cycling experiments were performed inside the fringe field of the 9.4 T magnet. An overview of the fringe field as a function of the detection coil center to center of the sample tube is given in figure . Samples were prepolarised at 9.4 T before being shuttled to a fringe field region of 1.9 T as indicated in figure . The sample transport was performed using a stepper motor driven sample carriage operated at a fixed velocity of 1 m s -1 , as described in reference 79. Typical shuttle times were on the order of ∼ 300 ms. Signal detection was performed by shuttling the sample back into the detection region of the high field NMR magnet and applying a π 2 pulse. Longitudinal relaxation time constants at 16.5, 9.4 and 1.9 T were determined with a standard inversion recovery experiment. For T 1 measurements at 1.9 T the sample was first prepolarised at 9.4 T, the magnetisation then inverted and shuttled to 1.9 T as described above. After a variable recovery period the sample was shuttled back to the detection region of the high field magnet to indirectly observe its recovery to thermal equilibrium at 1.9 T.