Revisiting p-11B fusion cross section and reactivity, and their analytic approximations

Abstract

Proton-boron fusion is experiencing a renewed interest as a possible energy source. The reaction is aneutronic and does not involve radioactive species. It has recently been induced by means of high-power lasers. Ignition of H-11B fuel, however, remains challenging because of the low reactivity and high radiative losses of the plasma at temperatures attainable in present-day fusion devices. Ideal ignition has been demonstrated only lately (and marginally), thanks to revisited cross section data. Reliable, agreed and fit-for-use cross section and reactivity data remain indispensable for further progress in the field. We propose a reference p-11B fusion cross section up to 10 MeV, mostly on the basis of recent measurements. We have developed an analytic approximation for the cross section and, through that, calculated the thermal reactivity. We also provide an analytic approximation for the reactivity, in the temperature range 10–500 keV, which is intended to update that of Nevins and Swain (2000 Nucl. Fusion 40 865), generally taken as a reference. Above 30 keV, our reactivity is substantially higher than that of Nevins and Swain. The gap increases with temperature, reaching e.g. 12% at 100 keV and 50% at 500 keV. Considering also the suprathermal contribution elicited by the fusion-born α’s, we anticipate a potential 50% increase already at 300 keV. Such a higher reactivity is expected to appreciably relax the ideal ignition temperature of H-11B fuel.