Coolant assembly of a DNP apparatus

A coolant sub-assembly for use in a DNP apparatus. The sub-assembly comprises: a number of concentric jackets (7,14,16,17) surrounding an inner bore tube (6) having first and second opposed ends. The jackets are adapted to inhibit heat flow to the inner bore tube (6), a DNP working region (21) being defined within the inner bore tube (6) where a DNP process will be performed on a sample in the DNP working region. A coolant supply path (2) extends adjacent an outer surface of the inner bore tube (6) at the DNP working region (21) in order to cool said outer surface, whereby a sample holder assembly (18) can be inserted through the first end of the inner bore tube to bring a sample holder into the DNP working region and can be moved through the second end of the inner bore tube. An auxiliary coolant supply path (11a,11b) supplies coolant to a sample, located in use in the sample holder at the DNP working region, through one or more apertures in the inner bore tube wall at the DNP working region (21). One or both ends of the inner bore tube (6) opens into a coolant waste path for conveying coolant away from the inner bore tube, and wherein the coolant, auxiliary coolant, and waste paths are coupled to pumping means in use to cause coolant to pass along the coolant, auxiliary coolant and waste paths.