Optimizing Electron Generation for cone-in-shell Fast Ignition with CH Foil

Electron-driven fast ignition is a promising inertial confinement fusion scheme that separates the compression and heating phases, reducing symmetry and target requirements. However, challenges in the heating phase, particularly in cone-in-shell designs, must be addressed. Ideally, a short-pulse laser interacting with the cone generates relativistic electrons at the cone tip, which then deposit energy into the compressed fuel. In practice, the pedestal of high-intensity lasers creates a pre-plasma 10s to 100s of microns in front of the cone tip. This causes the main pulse to interact with the pre-plasma, leading to electron beams being generated at the cone’s sidewalls instead of its tip. As a result, the electron beam is more dispersed, has a lower energy density, and exhibits significant shot-to-shot variability.

To address this, we conducted an experiment at the OMEGA-EP laser facility to investigate the use of CH foils at the cone entrance as a method for mitigating pre-plasma formation. The rear surface of the cone was surrounded by Cu-doped plastic, allowing us to track fast electron propagation via Cu K-alpha photon emissions. This approach enabled the assessment of electron generation and transport. Supporting radiation-hydrodynamic and particle-in-cell simulations provide insight into the underlying laser-plasma dynamics within the cone, demonstrating the potential of CH foils to stabilize electron generation and improve fast ignition performance.