  The advent of high-intensity pulsed laser technology enables the generation
of extreme states of matter under conditions that are far from thermal
equilibrium. This in turn could enable different approaches to generating
energy from nuclear fusion. Relaxing the equilibrium requirement could widen
the range of isotopes used in fusion fuels permitting cleaner and less
hazardous reactions that do not produce high energy neutrons. Here we propose
and implement a means to drive fusion reactions between protons and boron-11
nuclei, by colliding a laser-accelerated proton beam with a laser-generated
boron plasma. We report proton-boron reaction rates that are orders of
magnitude higher than those reported previously. Beyond fusion, our approach
demonstrates a new means for exploring low-energy nuclear reactions such as
those that occur in astrophysical plasmas and related environments.
