A first analysis of fast ignition of precompressed ICF fuel by laser-accelerated protons

The main parameters of the beam required to ignite a precompressed DT fuel, as foreseen by the recently proposed scheme of fast ignition by laser-accelerated protons (Roth et al 2001 Phys. Rev. Lett. 86 436), are studied by 2-D numerical simulations and a simple model. For simplicity, instantaneous proton generation at distance d from the compressed fuel and exponential proton energy spectrum, dn/depsilon proportional to exp(-epsilon/T-p), are assumed. An analytical expression and parametric numerical results are then given for the dependence of the minimum required beam energy on d, T-p and on the fuel density rho. For the parameters of Roth et al (d approximate to 4 mm; rho approximate to 400 g/cm(3)) the minimum total proton energy for ignition is about 40 kJ.