In order to obtain a thermal-reference comparison for our hyperpolarization experiments, we pneumatically shuttled the sample within 0.5 s using a vacuum pump from the center of a 2 T prepolarizing Halbach magnet to the detection region. Similar to the d DNP experiments, once the sample reached the center of the zero-field chamber, the guiding fields were rapidly switched off and the signal was detected. The NMR tube was assembled with PEEK pieces for efficient translation along the guiding solenoid. This is shown in the insert of Fig. .