Neutron Diffraction Studies of Flowing and Pinned Magnetic Flux Lattices in 2H-NbSe2

We report on detailed neutron diffraction studies of both pinned and moving magnetic flux line lattices in 2H-NbSe2. For field-cooled, pinned lattices, we are able to make a detailed quantitative comparison with the theory of Larkin and Ovchinnikov and find excellent agreement. In studies of the dynamics, we find that the longitudinal correlation length of the vortex lattice increases substantially when it is depinned and moving due to a current exceeding the critical current, and remains large when the lattice is repinned after turning the current off.