Scientific Coordinator: Sebastien Le Pape (CEA)
Ignition has been reached on the National Ignition Facility at the Lawrence Livermore National Laboratory (USA) in December 2022, with 2 MJ of laser light generated about 3 MJ of fusion energy, corresponding to a gain of 1.5. This is a major step toward a fusion power plant but the economic viability of such a fusion reactor requires to increase the gain by about a factor of hundred and to greatly increase the repetition rate, ultimately up to 10-15 Hz. It is generally acknowledged that an increase in gain and repetition rate requires to switch to a direct drive scheme, where laser beams directly irradiate the capsule. In addition, porous and nanostructured materials are today envisioned as part of the solution to high gain-high repetition rate fusion as they can mitigate hydrodynamic and parametric instabilities and facilitate a mass target production. This project aims at increasing the knowledge of the underlying fundamental physics of laser-porous matter interaction and its impact on inertial confinement fusion (ICF).
The project stands on three pillars: (i) to develop the theoretical framework (and benchmark it through dedicated experiments) that can model these new materials in integrated simulation codes,(ii) to assess the viability of a foam-based target design to mitigate the harmful effects and to reach ignition,(iii) to investigate the benefit of using nano-structured materials in a fusion reactor. The first axis implies the joint development of models (based notably on state-of-the-art simulations) and new diagnostic approaches (such as ultra-fast coherent imaging) to shed light on the basic mechanisms involved in the transition from a porous microstructure to a plasma under the effect of laser radiation or a strong pressure. The impact of these initial conditions on the plasma equation of state and on laser-plasma interaction will be studied. The second axis implies to take an integrated approach, building on the progress made on the first axis, to design an ignition/high gain experiment, using foam-based targets less prone to degradation mechanisms (mix or compression asymmetry) known to be a significant source of yield reduction in direct drive implosions. The ability of the proposed new design(s) to solve the mix issues will be assessed both numerically and experimentally. The third axis will be dedicated to study, both theoretically and experimentally, how a porous first wall will survive the harsh laser fusion environment.
