Path to Increasing p-B11 Reactivity via ps and ns Lasers

Abstract

The Lawson criterion for proton-boron (p-11B) thermonuclear fusion is substantially higher than that for deuterium-tritium (DT) because the fusion cross section is lower and peaks at higher ion energies. The Maxwellian averaged p-11B reactivity peaks at several hundred keV, where bremsstrahlung radiation emission may dominate over fusion reactions if electrons and ions are in thermal equilibrium and the losses are unrestricted. Nonequilibrium burn has often been suggested to realize the benefits of this aneutronic reaction, but the predominance of elastic scattering over fusion reactivity makes this difficult to achieve. The development of ultrashort pulse lasers (USPL) has opened new possibilities for initiating nonequilibrium thermonuclear burns and significant numbers of p-11B alpha particles have been reported from several experiments. We present an analysis that shows that these significant alpha yields are the result of beam fusion reactions that do not scale to net energy gain. We further find that the yields can be explained by experimental parameters and recently updated cross sections such that a postulated avalanche mechanism is not required. We use this analysis to understand the underlying physics of USPL-driven nonequilibrium fusion reactions and whether they can be used to initiate fusion burns. We conclude by outlining a path to increasing the p-11B reactivity towards the goal of achieving ignition and describing the design principles that we will use to develop a computational point design.

Revisiting Experimental Signatures of the Ponderomotive Force

“…Naively, one expects direct irradiation to convert laser energy more efficiently into fusion yield, in part because fusion can occur both in the neighbourhood of the focus where all ion species are heated, and in the colder bulk of the target by ions accelerated out of the focal region. Anecdotally, recent experiments support this hypothesis [2].…”

“…Short-pulse lasers deliver their energy to the plasma in a time much shorter than the typical expansion timescale, and both electrons and ions achieve much higher momenta. These plasma conditions are far from the quasi-thermal equilibrium of ICF, where burn has recently been achieved [1], and the question is open whether or not the dynamics admit a pathway to net energy gain [2]. Short pulse lasers have successfully driven high-yield beam fusion experiments [3,4], which can in turn be translated into novel high-flux, ultra short-pulse ion [5][6][7] and neutron sources [8][9][10][11].…”

Alpha heating and avalanche effect simulations for low density proton-boron fusion plasma

“…For the aforementioned reasons, the scientific community turns towards charged-particle neutron-free fusion reactions with significant cross section and energy release. In this context, p-11 B fusion reaction is the most promising candidate for clean energy production [5][6][7], as: i) It is the only neutron-free fusion reaction (< 1% of the energy in neutrons) [5], ii) It produces three (3) iso-energetic charged alpha particles, with 8.7 MeV total energy, that can directly be converted into electricity, without passing through a thermodynamic cycle [4,8], iii) It doesn't necessitate the use of breeding technologies for the production of its components (p, 11 B) [8,9].…”

“…-1 -This is a just misconception, as the p-11 B fusion reactivity is only a factor of few lower than that of D-T nuclear fusion reaction [4,9,11]. The resonances of major interest for p- 11 B fusion are located at the center-of-mass energies of 163 keV (with a width of just 5 keV) and 675 keV (with a width of 300 keV) [8].…”

Perspectives on research on laser driven proton-boron fusion and applications

“…α-particles) could imply the additional potential advantage of allowing direct conversion of the produced energy from kinetic to electrical energy, without implying a thermodynamic cycle, hence the traditional production of electricity by turbines (as in current power plants, including fission reactors, but also future fusion reactors based on DT fusion). In principle, this may increase the efficiency of electricity generation [21].…”