Fusion is what powers the Sun and all stars in our Universe. Fusion is the joining of two or more separate atomic nuclei into a larger nuclei. Fusion can create energy because the mass of the input and output nuclei are not necessarily equal in mass. An overview of what fusion is and why it is so important can be seen on my previous post on Fusion for the Future. Many scientists in the field acknowledge that a rapid development of fusion is unlikely, much less a commercial development, but there is hope. A reasonable time frame may be half a century before we see a world powered by the same process which drives the Sun. It will be an almost entirely clean, limitless, reliable, and safe source of power.
The key to releasing the energy of the Sun is forcing the nuclei of atoms close enough together for them to overcome their electrical repulsion and allow the strong force which binds nuclei to merge the nuclei together. Such favorable conditions for atoms to smash into each other can only occur under extreme temperatures and pressures, like say at the center of a star, but it is almost impossible to hold a star on earth. Anything which is hot enough to undergo fusion is also hot enough to burn through any container, thus we must contain something without quite touching it. Enter the magnetic doughnut known as the tokamak. A tokamak is a toroidal or doughnut shaped container that uses magnetic fields to confine plasma. Plasma is a state of matter where all the atoms are ionized (the electrons that normally orbit the protons in the nucleus have escaped)—and at these temperatures the atoms contained in the tokamak are definitely ionized. Magnetic fields apply a force on the charged particles of plasma such that the plasma can be corralled and kept away from the walls of the container. In an actual tokamak huge magnets encircle the enclosure as shown in the figure here where the magnetic coils and the ITER plasma surface is shown. The colors and contour lines indicate the magnetic field strength which is not quite perfect, the lines are wavy, due to deviations from perfect symmetry in the structure because the tordioal magnetic field is made of a finite number of magnetic coils. The ITER tokamak will be huge. Check out the tiny little person (bottom left) in the image below.
The plasma instabilities inside a fusion reactor are a serious engineering challenge, but they are not a safety concern at all. Unlike a fission reactor, when a fusion reactor is compromised it does not go critical in a dangerous explosion (like a fission reactor would), instead it just fizzles out harmlessly. This technology is not perfect though because while some may claim that a fusion reactor would create no dangerous radioactive material in fact it would produce some radioactive material that would need to be handled. It is the walls of the reactor which will become slightly radioactive (through neutron activation). Conveniently though the half life of such radioactive waste materials is less than 100 years and could be entirely handled on site.
We should all be hoping for fusion. I spoke with Michel Claessens, the head of communications for ITER, and one of the questions I asked him was, what should the public know about fusion and ITER?
As much as possible. More seriously, I would be happy if people understood the differences between fission and fusion.And he has a point I think. Most people simply don't understand what is at stake and what our options our. If you are reading this then you are already more informed than most. Tell people about the difference between fusion and fission and encourage your government (no matter what country you live in) to follow a wise energy policy. While I was writing this article the United States changed its funding proposition for ITER which was a welcome change because at one point the United States looked like it would falter on its commitment to fusion research and ITER completely. This is an investment in our future and the Earth. I asked Claessens a question about this topic too, how important is worldwide collaboration in achieving a successful ITER project?
Worldwide collaboration is useful and even necessary - to pool and ensure the best use of resources (human and financial). The ITER project is so complex that no single country has the scientific and technological skills to build the machine alone. In addition, the international collaboration was seen by ITER fathers (Gorbachev and Reagan) as a way out to cold war.The idea of harnessing the power of the Sun on the Earth is so much more than just a scientific endeavor. It is a very human dream to hold the Sun (what culture does not have some kind of original creation story or explanation for the sun?) and it is possible that realizing this dream may bring us together for all of the right reasons.