Progress on the Development of Ion Based Fast Ignition

Results from research on fusion fast ignition (FI) initiated by laser-driven ion beams is encouraging so far. FI based on a beam of quasi-monoenergetic ions (protons or heavier ions) has the advantage of a more localized energy deposition, which minimizes the required total beam energy, bringing it close to the theoretical minimum of ≈ 10 kJ. High-current, laser-driven ion beams are excellent for this purpose, and because of their ultra-low transverse emittance, these beams can be focused to the required dimension, ~ 25 – 50 μm. Because they are created in ps timescales, these beams can deliver the power required to ignite the compressed D-T fuel, ~ 10 kJ / 50 ps. Our recent integrated calculations of ion-based FI include high fusion gain targets and a proof of principle experiment. That modeling indicates the concept is feasible, and provides confirmation of our understanding of the operative physical processes, a firmer foundation for the requirements, and a better understanding of the optimization trade space. Three four requirements for the success of this scheme include 1) the generation of a sufficiently monoenergetic ignitor ion beam (energy spread below ~ 10%), 2) with a sufficiently high ion kinetic energy (≈ 400 MeV for C), 3) along with a sufficiently high conversion efficiency of laser to beam energy, 4) and the ability to aim and focus the beam. This paper describes the theory and experimental progress in our research program, which is concentrated on fulfilling these requirements. An important benefit of the scheme is that such a high-energy, quasi-monoenergetic ignitor beam could be generated far from the capsule (≥ 1 cm away), so that the laser-target providing the beam may be protected from the implosion. If a beam made at that distance can be aimed, the need for a reentrant cone in the capsule is eliminated, a tremendous practical benefit. New schemes for laser-driven ion acceleration under experimental investigation at Los Alamos, the laser-breakout afterburner and radiation pressure acceleration, promise to deliver the necessary ion-beam performance. This paper summarizes the ion-based FI concept; the progress in developing a suitable ignitor ion beam, and the integrated ion-based FI modeling.