Laser experiment gives new visibility to pB11 fusion
This story is part of LPP’s November 4th, 2013 newsletter, available in PDF format here. Join the discussion at the Focus Fusion Society here.
While FF-1 is still some steps away from switching to the hydrogen-boron fuel combination known as pB11, other approaches are proving the reality of pB11 fusion, which produces no neutrons in the main reaction and no radioactive waste. In a report published in Nature Communicationsand summarized in an October news item, a French and American team of researchers announced that they had succeed in increasing the fusion yield in a laser-driven pB11 experiment about 100,000-fold from earlier experiments in 2009. While the yield of about 0.3 millijoules was small compared with the 400 J of laser energy delivered and even smaller compared with the energy needed to drive the lasers, it was a step towards demonstrating the potential for pB11 fusion energy, and the publication in Nature Communications gave some needed visibility to aneutronic fuels.
In the experiment at the École Polytechnique in France, a laser pulse of a few nanoseconds first created a plasma from a solid chunk of boron. Then a much shorter and more intense laser pulse of just a picosecond hit a thin foil sandwich of plastic, aluminum and gold. The interaction of the short laser pulse with the sandwich generated a huge electric field that accelerated a beam of protons from the hydrogen in the plastic toward the boron plasma. When the protons and the boron-11 nuclei (80% of the nuclei in the boron target) collided, fusion reactions occurred. Instruments then observed the alpha particles (helium nuclei) produced by the reactions.
The density of the plasma in these experiments, at 1022 ions/cm3, was higher than plasma densities yet achieved in FF-1 using deuterium, but the duration of the reactions of one trillionth of a second (10-12 s) was much shorter than the lifetime of FF-1 plasmoids, some 10 ns (10-8 s) or so. The 100,000-fold leap in fusion yield, however, is not atypical of the jumps in output that can occur in fusion research.
