In principle, nuclear fusion is a simple process. All you have to do is push two suitable atomic nuclei close enough together for them to overcome their mutual electrical repulsion (since both are positively charged) and they will merge. This merger releases oodles of energy. The usual way to push nuclei together is to smash them into one another at high speed. In thermonuclear fusion (the sort that happens in the sun, in hydrogen bombs, and in traditional fusion experiments) that speed is achieved by heating the atoms up. But this, as Dr Naranjo and his colleagues realised, is not the only way to do things. You can, as they have done, simply accelerate a stream of nuclei to high velocity, and fire them into a stationary target.
And the experiment…
Dr Naranjo, by contrast, has devised a compact way of generating high voltages at much lower power using a so-called pyroelectric crystal.
Heating such a crystal (or, rather, warming it from -30°C to just above freezing point) deforms its structure in a way that concentrates positive charge in one place and negative charge in another. That results in a big voltage between the two. The researchers then amplified the effect of the positive charge by attaching a metal tip to the place where it was accumulating. This concentrated the electrical field in the same way that the point of a lightning conductor concentrates the stroke.
Dr Naranjo used this effect two ways: first to strip deuterium atoms of their electrons and second to repel the resulting stream of deuterium nuclei at high speed towards a target containing more deuterium. When two deuterium nuclei (each composed of a proton and a neutron) fuse, the result is a type of helium composed of two protons and a neutron, a free neutron, and a lot of energy. The bombardment also produces a lot of X-rays. By counting the neutrons and measuring the X-rays the researchers estimate that about 1,000 pairs of deuterium nuclei were fusing every second.
This is, as they are the first to admit, a long way from producing a significant amount of energy. And although they reckon they could boost the fusion rate 1,000-fold with better apparatus, that still might not reach the magic threshold of producing more energy than it takes to run the experiment. Beyond that, they are understandably unwilling to speculate.