Development of Large-Volume Diamond Anvil Cell for Neutron Diffraction: The Neutron Diamond Anvil Cell Project at ORNL

Ten years ago, Dave Mao, director of Energy Frontier Research in Extreme Environments (EFree), a Department of Energy (DOE) energy frontier, recognized the importance of neutron science for energy research. The subsequent establishment of a neutron group within EFree lead to the formation of an Instrument Development Team for SNAP, the dedicated high-pressure beamline at the Spallation Neutron Source at Oak Ridge National Laboratory in Tennessee. The core concept was to develop novel high-pressure techniques to expand the pressure range for neutron diffraction. A quite ambitious goal was set to reach half megabar levels (50 GPa), which at the time was considered extremely challenging. Here we will give a brief overview of the developments during the last decade in this novel area of research. An important factor was that during this period multicarat diamond anvils have become available grown by chemical vapor deposition (CVD), making research in this pressure range and beyond rather routine. This chapter shows the latest developments in large anvil and anvil support designs, compact multiple ton diamond cells, and new neutron methodologies. Achievements are illustrated with some examples of high-quality neutron diffraction patterns collected on sample sizes much small than conventional sizes.