Conditions to be satisfied to allow spontaneous fusion
Chemical reactions involve reshuffling the negatively charged electrons around the positively charged nuclei of atoms. Nuclear reactions control what happens one step deeper into the atom: they affect the nuclei themselves. Two kinds of such reactions exist. Fission is the best known of the two. It relies on the breaking of large nuclei into smaller daughter nuclei. All present-day nuclear reactors for the production of electricity rely on this process. Nuclear fusion, the second type of nuclear reaction, refers to the merging rather than breaking of small, light nuclei to form a heavier nucleus.
According to Einstein's famous law "E = m c**2", the difference in the summed masses of the fusion fuels and the fusion products is released in the form of energy. This energy manifests itself as kinetic energy: the fusion products have a very high birth speed.
The main difficulty the nuclear fusion process is facing is the fact that nuclei of atoms are positively charged and thus tend to repel one another. To overcome the repellant Coulomb force, the nuclei have to be accelerated to very high energies so that the distance between the nuclei can be made so small that the repellant force is dominated by the nuclear force. At first sight the solution seems straightforward: place the particles in a particle accelerator so that they collide with each other at high speed. The probability that particles merge under these circumstances is, however, small. It is much more likely for the particles to ricochet than to actually merge. And even if one would manage to realize fusion reactions in such a way, their number would never be sufficiently large to make a commercial fusion power station, a machine that delivers more fusion energy in the form of electricity than its components consume to start up the fusion reactions in the first place.
A possible solution is inspired on the burning fusion furnace of the sun in which large quantities of very hot gas particles are confined by gravitational force. This force keeps the energetic particles sufficiently long in the core of the star to allow fusion processes to take place sufficiently abundantly to realize a net energy surplus. Realizing fusion thus requires building "miniature suns". Two questions have to be answered affirmatively for that: Can we heat a gas to the high temperature required for fusion, and - provided we manage to achieve this first goal - can we keep the particles sufficiently long in a machine which is many orders of magnitude smaller and less massive that the sun?