Proton-boron (pB) fusion has long been seen as the grail of energy production for mankind. Indeed, the reaction (p + B11 -> 3 He⁴ + 8.7 MeV) does not produce neutrons, unlike the deuterium–tritium fusion (D-T) reaction, implying little activation of materials and hence a very low amount of radioactive waste. Therefore, pB fusion is clean and ecologically acceptable. In addition, it produces only charged particles with the potential advantage of allowing direct energy conversion, without a thermodynamic cycle. Thus, this might dramatically enhance the efficiency of electricity generation. However, the pB reaction requires unpractical temperatures to be thermodynamically triggered in the laboratory, thus explaining why research has focused on D-T, leaving pB as a remote, second step.

However, several recent experiments using laser-plasma approaches have shown very high yields in α-particle production, thus reviving pB fusion, which is nowadays considered a hot topic in both experimental and theoretical physics. Recent experiments performed with high-energy short-pulse lasers produced up to 1e11 α-particles per shot, and additionally provided the evidence of acceleration of α-particles above the value of a few MeV allowed by the kinematic of the fusion reaction. Indeed, these lasers can produce more energetic protons that can directly transfer part of their energy to the reaction products, thus, in turn, producing high-energy α-particles. This opens the possibility of triggering reactions which are useful, for instance, for the production of radioisotopes of medical interest.

Although interesting, all current results remain far from energy breakeven which corresponds to 2e15 α-particles generated per shot per kJ laser energy. Achieving breakeven and gain relies on the possibility of departing from the thermal equilibrium of classical inertial confinement fusion (ICF) experiments and initiating an avalanche or chain reaction. Several numerical works showed that a fusion flame could be ignited in solid-density hydrogen-boron fuel under ps-PW laser irradiation and the effect of magnetic confinement at field strengths of the order several kTesla. Although being preliminary and controversial, such results confirm the interest in continuing the investigation of laser-driven pB fusion, in particular on the role of magnetic fields acting to confine both protons and α-particles and affecting the generation of α-particles in the boron target.

The aim of this Special Issue is to collate original research and review articles with a focus on understanding the mechanism of proton-boron fusion in laser-produced plasmas and, in particular, the possible implications for future energy production by fusion, and the possibility of developing high-brightness alpha-particle sources for applications (including the production of radio-isotopes for medical applications).

Potential topics include but are not limited to the following:

• Recent results in laser-driven proton-boron experiments
• The onset of avalanche processes in proton-boron fusion and the quest for breakeven
• Development of high-brightness high-repetition-rate portable alpha-particle sources
• Alpha particle sources for production of short-living radioisotopes for medical applications
• Development in diagnostics for proton boron experiments
• Advancements in numerical simulations of proton-boron fusion and alpha-particle generation
• Laser systems for development of alpha-particle sources
• Advanced targetry for high-repetition-rate laser-driven experiments
• Proton-boron laser experiments in the context of laboratory astrophysics
• Non-thermal proton-boron fusion induced by lasers
• Hybrid approach to proton-boron fusion for energy
• Developments of hydrogen-boron implosion experiments