Cone-Guided Fast Ignition with no Imposed Magnetic Fields

TL;DR

This study uses advanced simulations to analyze cone-guided fast ignition, revealing how magnetic fields and electron spectra influence the energy required for ignition in inertial confinement fusion.

Contribution

It introduces a comprehensive simulation approach to evaluate the effects of magnetic fields and electron energy spectra on ignition energy in cone-guided fast ignition.

Findings

Magnetic self-guiding reduces ignition energy from 30 kJ to 20 kJ.

Realistic electron spectra increase ignition energy to over 80 kJ.

Including full Ohm's law raises ignition energy above 40 kJ.

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 E_f^{ig} = 30 kJ. This is about 3.5x the minimal deposited ignition energy of 8.7 kJ for our fuel density of 450 g/cm^3. Including E and B fields with the resistive Ohm's law E = \eta J_b gives E_f^{ig} = 20 kJ, 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 \nabla n \times \nabla 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 = \eta J_b, full Ohm's law). This stems from the electrons being too energetic to fully stop in the optimal hot spot depth.