A Novel approach for Inertial Fusion: Microbubble Implosion

Nuclear fusion reactions are exploited and studied for a number of applications. The most challenging and ambitious one is the production of energy, aiming to replicate on Earth the mechanism by which stars sustain themselves. After tens of years, several open questions and challenges remain before that ambition is realized and nuclear fusion energy becomes the norm. Indeed, different approaches are still being investigated, each with its own ramifications. Microbubble implosion (MBI) is a novel concept that may be developed to achieve in a future nuclear fusion industrial applicability, as a branch of Inertial Confinement Fusion (ICF). The irradiation with a femtosecond of a high-power laser (HIL) pulse of a micrometric target, which has a spherical empty cavity at the center, can redistribute the ionization electrons. The charge unbalance leads to the implosion of the cavity walls, reaching a density theoretically in the order of 1034 m−3 . This extreme condition lasts only for tens of femtoseconds and, therefore, is a highly out of equilibrium phenomenon. It is possible to take advantage of this. In thermonuclear plasmas, radiative losses via Bremsstrahlung significantly cool the plasma and can be detrimental. In MBI, the interaction time is so short that Bremsstrahlung losses are not the dominant loss mechanism. In typical fusion configurations, these losses represent the primary obstacle. Concerning the sustainability of the approach, it is highlighted here that the energy per pulse required is in the Joule order, and this is already achieved for femto-second laser systems. This research focuses primarily on the study of p-B11 fusion within the MBI framework. This opens the possibility of considering not only potential energy applications but also alpha-particle production, given that in Nature the vast majority of alpha sources originate from radioactive decay of heavy elements. Both results would be relevant to applications. To investigate this possibility, we conducted numerical and analytical analyses, modeling a submicrometric hollow target constituted by an external gold layer and two internal layers of boron and hydrogen. Moreover, EPOCH PIC simulations are presented to support some early hypotheses of the concept. The reactivity ⟨σv⟩ is obtained and presented with a preliminary optimization of the target and energy production estimates.