Visualizing Fast Electron Energy Transport into Laser-Compressed High-Density Fast-Ignition Targets

Recent progress in kilojoule-scale high-intensity lasers has opened up new areas of research in radiography, laboratory astrophysics, high-energy-density physics, and fast-ignition (FI) laser fusion. FI requires efficient heating of pre-compressed high-density fuel by an intense relativistic electron beam produced from laser–matter interaction. Understanding the details of electron beam generation and transport is crucial for FI. Here we report on the first visualization of fast electron spatial energy deposition in a laser-compressed cone-in-shell FI target, facilitated by doping the shell with copper and imaging the K-shell radiation. Multi-scale simulations accompanying the experiments clearly show the location of fast electrons and reveal key parameters affecting energy coupling. The approach provides a more direct way to infer energy coupling and guide experimental designs that significantly improve the laser-to-core coupling to 7%. Our findings lay the groundwork for further improving efficiency, with 15% energy coupling predicted in FI experiments using an existing megajoule-scale laser driver. Fast-ignition laser fusion involves directing an intense relativistic electron beam onto a fuel target. Experiments and simulations now enable a visualization of the location of fast electrons and the energy-coupling mechanisms at play.