The recent success in achieving break-even and target gain in inertial confinement fusion (ICF) has stimulated interest in extending the results to a regime where fusion becomes a viable source of energy. While indirect drive fusion results continue to show improvements, the fundamental physics limitations prevent extending this design to high gains without significant improvements [1] [2]. One attractive alternative is Fast Ignition (FI) [3]. FI separates the compression and heating phases of the ignition process. The heating to initiate ignition is produced by particles generated by a short pulse laser. Two options are currently being considered, proton FI (PFI) and electron FI (EFI). The charged particle focusing generated by an high intensity short pulse laser proved to be difficult but improvements on previous methods have been suggested to overcome these difficulties [5].
The focus of the experiments at Apollon will be to improve the understanding of the underlying complex electron physics to develop a predictive capability with the models and simulations for the electron FI platform. The challenge with EFI is twofold: 1) Collimating the electrons to minimize spatial spread so that the maximum number of electrons arrive at the hot spot and 2) generating an electron energy distribution that is designed to maximize the energy deposition at the hot spot. The two issues are correlated. As the electron propagates to the hot spot, the electrons undergo some degree of energy loss and scatter before depositing their energy in the hot spot. The efforts in this proposal will be to address the two effects with the goal of eventually independently improving these components in simulations and models.
Our goal in this Apollon campaign is to shoot a large number of shots, vary target types and laser conditions to understand where the scaling laws of short pulse high intensity that control the energy of the non-thermal electrons and collimation. As opposed to previous work, we hope to measure additional controlling quantities to understand the impactful scaling laws at a fundamental level.
This work constitutes a critical step towards inertial fusion energy using the fast ignition approach. If successful, it would open up the design space for a platform realizing fast ignition concepts for the next-step in IFE development.