Towards more robust ignition of inertial fusion targets.*

Following the 3.15 MJ fusion milestone at the National Ignition Facility, the further progress of inertial confinement fusion requires the development of more robust ignition concepts at current laser facility energy scales. This can potentially be achieved by using relativistic electron beams to auxiliary heat the hotspot of low convergence wetted foam implosions where hydrodynamic and parametric instabilities are minimised. Here I present the first multi-dimensional hydrodynamic, Vlasov–Maxwell and particle-in-cell simulations to model this collisionless interaction, only recently made possible by access to the largest modern supercomputers. The key parameter of interest is the maximum fraction of energy transferred from the electron beams to the hotspot plasma. The simulations indicate that significant coupling efficiencies are achieved over a wide range of beam parameters and spatial configurations – see https://doi.org/10.1063/5.0120732. The generation of suitable electron beams via petawatt class laser-plasma interactions, as well as collisional stopping in the fusion fuel, are modelled and optimised using a multi-scale automated workflow manager utilising Bayesian optimisation. Results indicate peaked, beam-like electron distributions develop as hot electrons propagate through the collisional fusion fuel surrounding the hotspot. The implications for experimental tests on the National Ignition Facility are discussed.