Cone-guided fast ignition with no imposed magnetic fields

Lawrence Livermore National Laboratory, Livermore, CA 94550, USA

^a e-mail: strozzi2@llnl.gov

Published online: 15 November 2013

Abstract

Simulations are presented of ignition-scale fast ignition targets with the integrated Zuma-Hydra PIC-hydrodynamic capability. We consider a 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, ignition can be achieved with fast electron energy E_f^ig = 30kJ. This is 3.5× 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 = ηJ_b gives E_f^ig = 20kJ, while using the full Ohm's law gives E_f^ig > 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 E_f^ig to (102, 81, 162) kJ for (no E/B, E = ηJ_b, full Ohm's law). Such electrons are too energetic to stop in the optimal hot spot depth.