High resolution imaging of k-alpha x-rays using an elliptically bent crystal

The x-ray ray-tracing package Shadow is used to determine the optimal elliptical surface for high-resolution x-ray-imaging of laser-irradiated targets. The crystals will be deployed in experiments to diagnose the transport of x-ray generating electrons that are accelerated by the laser. High-current, relativistic electron beams propagating through solid targets may be susceptible to filamentation instabilities in which the beam breaks up, along its transverse dimensions, into a system of smaller co-propagating current threads. Experimentally, high-resolution, coherent-transition-radiation imaging of the rear surface of high-current-carrying targets has shown a structured pattern of emission that is indicative of electronbeam filamentation. For target thicknesses greater than 30 microns, filaments with radii around 2 to 3 microns were separated by up to 10 microns. However, no independent confirmation of the filamentation has been obtained. The resolving power of spherically bent crystals is limited by spherical aberration to around 15 microns making them incapable of detecting such structured patterns. By eliminating spherical aberration, elliptically bent crystal provide the potential to produce images with a spatial resolution down to 5 microns. Results comparing the x-ray imaging properties of elliptically bent and spherically bent crystals will be presented.