Aneutronic Nuclear Fusion Reactor + Engine Proposal

Here is some brief theory behind Aneutronic Fusion, a form of nuclear fusion which produces no harmful neutron radiation, eliminating the need for heavy shielding in energy plants and spacecraft engines. The reaction can be initiated under a picosecond laser pulse which is aimed at a metal target producing protons which can fuse with Boron atoms in the molecular lattice of the fuel substance. The alpha particles generated from this reaction can be converted directly to an electrical current using alpha voltaics. Due to the reaction being initiated by the laser beam, all radiation emitted stops as soon as the laser is switched off allowing for the highest level of control for a nuclear reaction.

Due to the nuclear test ban treaty, nuclear propulsion spacecraft engines have never been deployed in space, creating a huge set back in our ability to reach deep space. Aneutronic fusion, if viable, could act as a loophole around the test ban treaty as it is impossible for this technology to be used as a weapon as no harmful radiation is generated.

Other plans for nuclear propulsion engines include gas core electromagnetic fission reactors which could generate high levels of ultraviolet photon pressure to propel a spacecraft, however such a technology would not be viable until the late 21st century.

Helium-3, Lithium-7 and Boron-11 are the isotopes which can be fused with protons to produce energy.

in p-11B fusion the proton and boron-11 nucleus are fused and form a short-lived excited state of a carbon-12 nucleus, sometimes called a Hoyle state in the Triple-Alpha fusion cycle. The unstable carbon-12 Hoyle state then decays by gamma decay into beryllium-8 and an alpha particle. Beryllium-8 then decays by gamma decay into two helium nuclei.

the p-11B fusion reaction requires the most energy, however 11B has a large cross-section for alpha particles and the reaction gives off 3 alpha particles for every 1 consumed, so in principle a critical mass for fusion can be reached.

The p –7Li reaction has no advantage over p –11B, given its somewhat lower cross section. But this is mitigated by having double the power output.

Helium-3 is an ideal potential aneutronic fusion fuel, however it is only present in very low quantities on the Earth and requires nuclear fission reactions to make it, which removes the purpose of a self-sustaining fusion energy industry altogether. The far side of the Moon, Mercury, Mars and gas planets such as Jupiter and Saturn have the largest quantities of Helium-3 in the solar system, so space exploration is required to make Helium-3 fusion possible. Hence Helium-3 is most likely to be a second or third generation nuclear fuel.

Therefore Boron-11 is currently the best isotope on earth for studying the aneutronic fusion reaction process and to design a nuclear reactor/engine around the principle, at least until lunar mining gets underway which may not be until mid to late 21st century. Therefore the development of these principles should continue with 11B aneutronic fusion research so the technology exists to use Helium-3 when a system exists to have it on tap from the moon.