Editorial: Non-Local Thermodynamic Equilibrium (NLTE) Hydrogen-Boron Fusion

The HB reaction creating 3 α particles was attractive from the beginning of research in terrestrial fusion energy applications because no neutrons are produced in this case. However, the reactivity <σv> (σ is the fusion cross section and v is the relative velocity between reacting species) of HB fuel at temperatures of 20 keV is five orders of magnitude less than that of deuterium–tritium (DT) fuel. The <σv> of HB at about 600 keV reaches a rate comparable to that of DT at 20 keV. The 600 keV temperature is extremely high for a laboratory reactor. This seems to be the main reason why the HB clean fusion was neglected on the road to achieve a clean and safe solution to the energy problem, while most of research and development was done for DT fusion. Recently, in a series of publications, it has been suggested that for the HB case, we do not need to reach a local thermal equilibrium (LTE) at such a high temperature before fusion becoming viable. Thanks to the development of lasers, we can effectively accelerate protons in a plasma, inducing the HB interaction at its maximum cross section, at about 600 keV center-of-mass energy. In addition, the reaction yield might increase significantly without reaching extremely high temperatures because of a further non-LTE (NLTE) effect. Indeed, it has also been suggested that the avalanche or chain reactions based on suprathermal ions energized by elastic scattering with the α′s may play an important role in increasing the yield of fusion reactions. The controlled nuclear fusion reactor suffers from the need of thermal pressures at the temperatures of hundreds of million Celsius requested for ignition. Frontiers is publishing five articles about proton–boron nuclear fusion in the NLTE regime. In the following five articles, research is done to check the physics principles for the novel idea that a fusion reactor can be achieved by nonthermal conditions without the need for heating up to temperatures as high as in the center of our Sun. These articles are as follows: