Will another old promise of science soon become reality? – News from research on nuclear fusion
The „Fridays for Future“ demonstrations are reaching new climaxes, the coalition in Germany decides on a multi-billion climate package, and at the global climate summit in New York government representatives and CEOs of multinational corporations and their PR strategists are trying to make a name for themselves as well-meaning climate protectors. It appears that the question of our future energy production and its harmful waste has finally reached the center of public attention and debate.
And it is precisely at this time, without this receiving much public attention, that scientists are making progress in an area that could solve the problems of global energy supply once and for all: the peaceful use of nuclear fusion. This is about nothing less than finally fulfilling the dream of unlimited, clean and safe energy from the thermonuclear fusion of atom nuclei, the very same that supplies our sun and stars with seemingly endless amounts of energy.
The history of nuclear fusion research is already 80 years old. Since the 1930s, physicists have known that under very high pressure and high temperature, hydrogen nuclei fuse into helium nuclei – and that it is this mechanism (as well as the fusion of higher nuclei) that enables the sun to generate its energy. The energies that are thus released are much higher than in the reverse process,in which heavy atomic nuclei are split,which nuclear power plants have used for more than 60 years. The reason for the energy gain is that during the fusion of light atomic nuclei leads to a loss of a small amount of mass. This mass defect manifests itself directly in the (kinetic) energy of the particles produced. According to Einstein’s famous formula E=mc² even withthe low amounts of lost mass this energy is enormous: Because this mass (m) is multiplied by the square of the speed of light (c²).
As early as in the early 1940s, the American researcher (and later father of the hydrogen bomb) Edward Teller and the Italian Enrico Fermi (who was the first to perform controlled nuclear fission) developed first ideas for power generation on the basis of controlled nuclear fusion. Their basic concept remains the basis for nuclear fusion researchers today: a deuterium-tritium plasma (deuterium and tritium are isotopes of hydrogen, i.e. a proton is joined by one, respectively two neutrons) is heated to several million degrees in a kind of microwave and then enclosed and controlled by means of a magnetic field (such a plasma consists of charged particles and can therefore be controlled by such fields). As of a temperature of about 100 million degrees the mixture ignites and releases the fusion energy (in fact, the precise ignition temperature depends on the particle density of the plasma).
It is difficult not to fall into ecstatic excitement in view of the practically unlimited possibilities of nuclear fusion. The energy thus released is safe, carbon-free and its required initial materialsare abundantly available. The primary fuel – hydrogen isotopes – can be found in normal ocean water. One kilogram of the deuterium-tritium mix is enough to supply an entire city with energy for a very long period. A functioning reactor would only need five kilograms of hydrogen to produce the energy equivalent of 18,750 tons of coal, 56,000 barrels of oil or the amount of energy 755 hectares of solar collectors produce in one year. Unfortunately, a 100 million degree hot mixture of hydrogen nuclei is so difficult to control that a well-known joke among physicists is that nuclear fusion is the most promising technology of the future – and will remain so forever. The reason for that is that the ultra-hot plasma must be kept under control, since it immediately cools down upon contact with the „outer world“ (e.g. the container walls), which interrupts the fusion instantly. To this end, researchers and engineers are developing enormous magnetic fields. But to maintain these fields with high performance and at the same time great precision is the technological challenge that must be mastered and on which top scientists all over the world have been working for decades. So far, they have done so with only moderate success –and this at very higher costs. The total projected costs of them main thermonuclear experiment today stands at over 20 billion euros to date and will go as high as 60 billion euros according to some experts (it is already the by far most expensive experiment in the history of science). The ITER experimental reactor is being financed by an international consortium and built in the French town of Cadarache. It is expected to produce its first results from 2030 onwards. However, nobody expects a net electricity output before 2040 at the earliest.
However, despite all these tremendous costs and the long time horizontheir experiments entails the nuclear fusion researchers at ITER do not yet have a particular problemon their screens. The deuterium-tritium fusion reaction produces neutrons of very high energy (14.1 MeV). Since they are electrically neutral and are therefore not influenced by magnetic fields, these neutrons collide in large numbers at very high speeds with the material of the reactor’s container, causing enormous damage to it. After only one or two years, the container will thus have to be replaced, which would pushes the operating costs of a fusion reactor to unacceptable heights. In addition, the neutron bombardment in the container material creates radioactive nuclides, which generates radioactive waste and thus makes the disposal of the material yet more costly. The call for an alternative for the deuterium-tritium reaction, which does not have this problem, has been made by experts years ago. The next possible candidate is the boron-proton reaction. It is „clean“ as it produces three helium nuclei that have no major influence on their environment. Its problem: It requires about 30 times higher plasma temperatures to ignite!
Next to the government sponsored gigantic project a number of private companies have dedicated themselves to nuclear fusion research and are thereby taking a quite different route than the scientists at ITER. With alternative and much smaller reactor technologies, they want to generate electricity from fusion already in the next few years, thus much faster than ITER. A public-private race for the best fusion technology solution has developed. The example of the Human Genome Project showed us almost 20 years ago how fruitful such a race can be.
Instead of walking along the one and only one true (and very expensive) path like medieval scholastics (large-scale plasma held together by gigantic superconducting magnets), these companies are much more flexible in trying to pick up the jackpot of a functioning fusion reactor. They follow a whole variety of different ideas in order to possibly out of those find one functioning path. They are counting on that possible mistakes and insurmountable obstacles in any of these ideas are found much faster than in a few decades time and before billions of dollars have been burned. Thus in the thicket of problems of holding an ultra-hot plasma together, a viable path might soon emerge. And indeed, these private companies, backed by a few financially strong investors, have in recent months and years made considerable progress, without the public having noticed too much about it.
There are a number of different ways for physicists and electrical engineers to reach their goal of controlled nuclear fusion. Essentially, the problem involves three essential variables: The temperature (or velocity/energy of the particles in the plasma), the density of the plasma (number of particles per volume) and the inclusion time (how long the plasma is held together). As of a critical temperature, which is necessary for the positively charged atomic nuclei to overcome the electrical repulsion force(in the deuterium-tritium reaction the mentioned 100 million degrees) only the product of density and inclusion time is important. According to a rule of thumb, their product must be greater than 1014 seconds per cubic centimeter. Thereby it does not matter whether the density is low and the inclusion time high (as with ITER, where the long inclusion times mean a lot of effort – and therefore costs) or the inclusion time very short and the density very high (as with LIFE – Laser Inertial Fusion Energy – another project financed with public money, which has beenhalted in the meantime: here the high densities were to be achieved with strong laser pulses). In fact, in the middle between these two extremes, in the range of medium range inclusion times and medium range densities, lies a very large playground, which has so far been largely left untouched by the publicly financed projects. But in the opinion of many plasma physicists, this is where the most promising opportunities for a controlled nuclear fusion reactionlie.
It is clear to everyone involved: The path towards a functioning fusion reactor does not lead via unknown physics. Rather, it is primarily aquestion of good engineering work. And it is precisely here wherethe private companies have made significant, perhaps even decisive, progressin the last few years. During a recent visit to one of these companies the author of these lines was able to see this for himself. At first sight the progress made might not sound that spectacular. The properties of the plasma that determine inclusion times (the so-called “containment parameters”) prove to be more favorable at higher temperatures than at lower temperatures! It is precisely this insight, however, that could prove decisive on the way towards a functional – and commercially viable – fusion reactor. Because one thing is clear: Due to the problems with the resulting fast neutronsdescribed, the deuterium-tritium reaction will most likely never deliver commercially usable fusion energy. We would need the much higher temperatures of for example the boron-proton reaction. The fact that the private companiesdepend on risk capital that is hungry for returns could in the end prove to be a decisive advantage. These companies simply cannot afford to turn to large (i.e. expensive), long-term and completely untested projects (which on top of that leave one important problem completely unconsidered). Rather, they must always decide step by step which next moveto take and justify these in front of their shareholders. In light of the nature of the described problems aroundthermonuclear fusion technology such a pragmatic approach might prove far more appropriate than betting on a single grandiose idea.
Commercially available fusion technology, if one day it were actually available to us, would represent a social paradigm shift. Were we really able to produce energy like the sun does and thus have access to the most efficient, safest and most environmentally friendly form of energy nature provides, we would certainly experience not only another major technological advance, but rather a leap forward in civilization itself, comparableto the invention of the steam engine that providedthe energy for turning the human society upside down 250 years ago.