Kinetic particle-in-cell modeling of proton-driven fast ignition in DT and alternate fuels

It is well known that the p11B fusion reaction [11B(p, α)αα] has many attractive features for use as an alternate fuel for fusion, most notably the absence of neutron production. Its cross section, however, is significantly lower than the traditional deuterium–tritium (DT) reaction and also peaks at much higher temperatures. For a bulk composite p11B target, bremsstrahlung losses dominate over gain from fusion reactions for all temperatures. Net energy from purely thermonuclear p11B fusion is possible only at high ion temperatures (∼100 keV) and when the electrons are considerably cooler than the ions, thus limiting bremsstrahlung losses. Kinetic ion effects can also possibly increase fusion reactivity. Such effects are important to consider in fast-ignition scenarios. We describe here a hybrid kinetic-fluid particle-in-cell model for proton-driven fast-ignition of fusion targets comprised of both DT and p11B with the goal of finding beam parameters sufficient for ignition of the fuel. The results of the model for DT targets are shown to be in good agreement with multi-fluid treatments previously reported. For p11B targets, we find that with sufficient beam energy, the necessary ion temperatures can be obtained, along with lower electron temperatures, for timescales on the order of the driver pulse length. The inclusion of kinetic effects such as large-angle ion scattering is beneficial to the fusion yield. Gains, however, are quite modest, and appear to be limited by electron–ion temperature equilibration on longer timescales.