Ablation-driven targets for electron-beam fusion: Density problem with very low-Z ablators

The behavior of DT-filled implosion targets with very low-Z (carbon) ablators irradiated by 1-MeV electrons is compared to that with intermediate- and high-Z ablators. The inner part of the pusher is of lower entropy due to decreased bremsstrahlung heating. The DT is shielded from compression until later in the energy pulse, when it is more strongly compressed. However, thicker ablators transfer less energy to the pusher; hence, diamond-carbon ablators perform better than graphite-carbon. Precompression of graphite-carbon with a laser does not reduce the minimum power required for break-even, but does lead to increased gain above break-even