Of all the stable elements hydrogen(deuterium) is the least well studied from a structural point of view. Not one of its crystal structures has been fully charecterised. This proposal is for beamtime to measure the termperature dependence of the atomic displacement paramteters and to determine the full structure of deuterium at 6 GPa. This will provide the first direct measurements of the debye temperature and the zero point motion as well as of the D-D distance. All these parameters provide fundamental insight into the nature of deuterium and provide targets for theoretical modelling.