Imploded Shell Parameter Estimation Based on Radiograph Analysis

High target density is an important condition for achieving ignition in direct-drive fusion experiments. High densities are momentarily created during a successful implosion. The OMEGA laser’s 60 beams heat the target, causing the surface to ablate and compress the fusion fuel.1 X-ray radiography is used to analyze the compressed target’s optical thickness, which in turn describes the target's density. The higher the optical thickness, the darker the shadow cast. By recording the intensity of the backlighter x rays across the radiograph, the radiograph gives an attenuation profile. In a simple model of the shell, the changing attenuation across the radiograph depends on three parameters: inner radius, outer radius, and central radial optical thickness. A FORTRAN program was created to calculate the variances of the estimates of these three parameters in the presence of measurement error and a finite number of attenuation measurements limited by the finite resolution of the imaging device. Choosing the optimum optical thickness for the target by adjusting the backlighter photon energy minimizes the uncertainties of these estimates