X-ray wavefront characterization with two-dimensional wavefront sensors: shearing interferometers and Hartmann wavefront sensors

Phase reconstructions from a two-dimensional shearing inter-ferometer, based on two orthogonal phase gratings in a single plane, and a Hartmann sensor are compared. Design alternatives for both wavefront sensors are given, and simulated performance of both the two-dimensional x-ray shearing interferometer and Hartmann wavefront sensor are presented for two different phase profiles. The first comparison is an evaluation of metrology on deuterium-tritium (DT) ice layers in an iner-tial confinement fusion capsule, and the second comparison is a high frequency " asterisk " phase profile, which tests the ability of these wavefront sensors to detect spikes of ablator material seen in DT fuel capsule implo-sions. Both of these sensors can measure the two-dimensional wavefront gradient of an x-ray beam, as well as the x-ray absorption. These instruments measure the two-dimensional wavefront gradient in a single measurement , and the wavefront sensor is located in a single plane, making them much less sensitive to vibrations than most other wavefront sensing techniques. 1 Introduction This article discusses methods for phase sensitive x-ray characterization in inertial confinement fusion. Fusion is the process that powers stars, and numerous efforts are under way to achieve laboratory demonstrations of breakeven, more energy released via the fusion process than input to initiate the fusion reaction. In man-made fusion, two light nuclei are brought together at sufficiently high density and for a sufficiently long time to overcome the Coulomb force between the two nuclei such that their respective nuclei are fused together. That process liberates more energy than is required to fuse the two nuclei together and hence is being pursued as an energy source. In man-made fusion, the two nuclei are generally deuterium and tritium due to the smaller coulomb barrier that must be overcome and the higher reaction rate at lower temperature than other possible reaction rates. In inertial confinement fusion the deuterium-tritium (DT) fuel is compressed to very high densities for a relatively short time. This compression is driven directly or indirectly by absorption of radiation, optical, x-ray, or ion, in a fuel capsule. This fuel capsule is composed of an outer ablator and an inner region containing deuterium and tritium. The radiation is absorbed by the ablator whose mass is ablated by the absorbed energy driving shock waves, which then compress the deuterium-tritium to high density and temperature where the deuterium/tritium ions can fuse together. This fusion process produces a neutron and an alpha particle …