Insufficient energy gain of pure proton–boron fuel for IFE: 1D radiation–hydrodynamic simulations

Deuterium–tritium has the highest reactivity and lowest ideal ignition temperature of the fusion reactions, but it poses engineering challenges in inertial fusion energy (IFE) applications associated with tritium supply and cryogenic target handling, as well as heat-transfer flow activation and reactor first-wall material damage by 14 MeV neutrons. Aneutronic fuel cycles, such as proton–boron (p¹¹B) fusion, may have reduced engineering issues but have significantly more demanding conditions to ignite and burn. Recent favorable updates to reactivity and the inclusion of suprathermal effects and non-equilibrium burn have prompted this reevaluation of ignition and gain of p¹¹B fuel for IFE. We have studied thermonuclear burn wave propagation in highly compressed BH₅ and B₂H₆ fuels using the HELIOS-CR 1D radiation–hydrodynamics code, which has been updated to use the latest p ¹¹B reactivity, a multiplier to approximate suprathermal effects, and temperature-dependent alpha particle transport. Starting from fast ignition-like isochoric initial configurations, we have identified the hot spot requirements for self-sustained burn wave propagation: at the density of 4000 g/cm³ and the hot spot temperature T_hs = 400keV, the ignition of BH₅ requires the hot spot areal density of 25 g/cm² and energy over 200MJ, while the ignition of B₂H₆ requires at least 70 g/cm². At T_hs < 200keV, achieving ignition is hardly possible. We have estimated the maximal fuel gain for pure p¹¹B fuel as a function of the cold fuel adiabat for fusion yields up to 3–5GJ and found that they are insufficient for IFE power plant operation.