Inertial Fusion Fast Ignitor: Igniting Pulse Parameter Window versus the Penetration Depth of the Heating Particles and the Density of the Precompressed Fuel

A key element of the fast ignitor scheme is the pulse of fast particles creating the igniting spark. In this paper, the dependence of the parameters (energy Ep, power Wp, intensity Ip) of such a pulse on the penetration depth R of the fast particles is studied by two-dimensional simulations of the evolution of a deuterium–tritium fuel, precompressed at density ρ, and heated by a beam of particles with assigned R. The ignition windows in the (Ep,Wp,Ip) space are found to depend very little on R over the interval 0.15 ⩽ R ⩽ 1.2 g/cm^2. At ρ = 300 g/cm^3, the minimum ignition energy is about 14 kJ; an optimal set of parameters (with energy and power about the required minimum, and intensity relatively close to the minimum) is Ep ≅ 17 kJ, Wp ≅ 0.85×10^15 W, and Ip ≅ 6.5×10^19 W/cm2 (achieved at R = 0.6 g/cm^2). The optimal energy scales with the density as Ep∝ρ^(−1.85). Scaling laws are also presented for the other pulse parameters and for the limiting energy gain.