X-ray diffraction studies of dynamically compressed diamond

Abstract

X-ray Diffraction Studies of Dynamically Compressed Diamond Purpose:We propose a series of experiments to use X-ray diffraction (XRD) to study material properties using the NIF. XRD is the best way to determine the structure, lattice deformation, and texture of materials. Advances in synchrotron XRD facilities in the past two decades have revolutionized the study of materials at static high pressure in diamond anvil cells (DACs) up to about 3 Mbar. The National Ignition Facility (NIF) has the potential to do the same for dynamic materials studies at high-pressure. Members of our scientific team have pioneered XRD on many smaller laser facilities around the world. Our results suggest that diffraction on solids approaching 100 Mbar may be possible on the NIF, providing access to new regime for matter at extreme conditions. Scientific Case:An understanding of the fundamental physics of the response of matter to rapid compression -be it shock or quasi-isentropic -remains an important, elusive challenge in the fields of laser-matter interactions and high energy-density physics. The capabilities of the NIF greatly expand capabilities in this burgeoning field, as the high energy and long shaped-pulse capability of this unique platform will allow the precise temporally-controlled compression of matter to many tens of Mbars, heralding a new era of high-pressure materials science, with the potential to uncover hitherto unknown highpressure crystalline phases and material properties.The aim of this proposal is to reach an understanding, at the atomic level, of the pathways taken to, and the final forms of, these new states of matter. The diagnostic of choice is nanosecond X-ray diffraction. This proven technique, pioneered on more modest laser platforms (at consequently lower pressures) by the applicants, affords the potential for direct monitoring of lattice deformation before, during, and after polymorphic phase transitions. We are firmly of the view that dynamic ultra-highpressure materials science on NIF will be an extremely fruitful area of study. There are many materials that we wish to interrogate as the field matures, with varying, but equally compelling scientific rationales. This consortium proposes an initial concentration on polycrystalline diamond targets using an angle dispersive camera.There are two persuasive reasons for this approach. First, the beauty of materials with the diamond cubic structure is that we can obtain single-crystal samples which are, for most purposes, 'perfect' -i.e. dislocation free. There is a strong line of reasoning that indicates these materials are better suited for theoretical modeling, both in terms of ab-initio calculations, and large (multi-million to billion atom) classical molecular dynamics calculations. Second, low-Z, strong and/or highly anisotropic materials, such as diamond and beryllium remain as candidates for ablator materials for ICF targets. Depending upon the target and drive-pulse designs, material phase, strength, texture, and lattice response may play a role in...