Cone-Guided Fast Ignition with no Imposed Magnetic Fields
Abstract
Simulations of ignition-scale fast ignition targets have been performed with the new integrated Zuma-Hydra PIC-hydrodynamic capability. We consider an idealized spherical DT fuel assembly with a carbon cone, and an artificially-collimated fast electron source. We study the role of E and B fields and the fast electron energy spectrum. For mono-energetic 1.5 MeV fast electrons, without E and B fields, the energy needed for ignition is Efig = 30 kJ. This is about 3.5x the minimal deposited ignition energy of 8.7 kJ for our fuel density of 450 g/cm3. Including E and B fields with the resistive Ohm's law E = η Jb gives Efig = 20 kJ, while using the full Ohm's law gives Efig > 40 kJ. This is due to magnetic self-guiding in the former case, and ∇ n × ∇ T magnetic fields in the latter. Using a realistic, quasi two-temperature energy spectrum derived from PIC laser-plasma simulations increases Efig to (102, 81, 162) kJ for (no E/B, E = η Jb, full Ohm's law). This stems from the electrons being too energetic to fully stop in the optimal hot spot depth.