Proton generation in cone targets for fast ignition of inertial fusion targets

Focused Energy has been exploring various ignition schemes in recent years to achieve high energy gain while reducing the laser energy requirements needed for commercially viable fusion energy. One of these approaches is proton fast ignition (pFI), which involves generating extremely intense laser-driven proton beams with energies reaching tens of kilojoules.

We have studied the generation and propagation of these proton beams within millimeter-scale cones to better understand the complex ion transport dynamics and magnetic field structures, which may contribute to the divergence of the proton beam. Realistic particle-in-cell (PIC) simulations have been conducted to maximize laser-to-proton conversion efficiency and minimize beam divergence in the pFI scenario.

Our previous studies have shown that a significant reduction in beam divergence can be achieved by using laser pulses with intensities of a few times 10^19 W/cm^2, focused on large spots to enable quasi-one-dimensional acceleration. The core idea presented here is to enhance proton beam focusing by adjusting the cone geometry, specifically the curvature of the proton-rich foil, the length of the cone, and the tip diameter, indicating that the cone geometry plays a crucial role in optimizing beam generation. This finding is significant not only for pFI but also for the generation of warm dense matter and various other applications.

We have estimated the energy requirements for a short-pulse laser needed to achieve high gain in a proton beam with optimized focusing. This estimation is based on a density distribution of deuterium-tritium (DT) obtained from cone-in-shell simulations [1]. This analysis will help assess the potential of pFI as an alternative approach for Inertial Fusion Energy.



References

[1] A. Mateo et al., “Implosion of Cone-in-Shell Targets for Proton Fast Ignition”, submitted to Nuclear Fusion (2025)