This breakthrough will likely lead to further acceleration, providing an unlimited clean energy supply. Fusion is seen as having great potential to become a sustainable, low-carbon energy source in the future. However, despite the remarkable headlines, Vilnius University (VU) scientists explained the experiment and its context in greater detail.
Mimics the processes in the deep interior of stars
“Energy is currently one of the most important topics in the world, with renewable energies a major focus. However, the use of renewables is limited by climatic conditions and the need for relatively expensive equipment. Another way of generating energy is to use nuclear fission reactions. Still, these processes in nuclear power plants use radioactive uranium, so there are dire consequences if they fail,” said Dr Mažena Mackoit, a researcher at the Faculty of Physics.
In nuclear fusion, on the other hand, although there is a nuclear reaction, the nuclei do not split. This absence of a chain reaction also eliminates the risk of explosions. In addition, nuclear fusion can use all the elements lighter than iron and yields several times more energy than uranium. Finally, this process does not release greenhouse gases.
“Fusion technology mimics the processes that take place in the depths of stars. To achieve thermonuclear fusion, we need very high temperatures in the laboratory, close to the sun, and high pressure. Furthermore, that heat needs to be concentrated into a small volume so that the nuclei are fused together into a single element, thereby releasing energy.
However, it is not easy to create artificial conditions that mimic those found in the sun. After all, we are talking about a few hundred million degrees Celsius. That is why we do not have a fusion reactor. In Europe, the Tokamak reactor, which uses electromagnetic confinement technology, has not yet succeeded in delivering a higher energy yield than the cost. However, the Americans have been able to achieve an energy surplus by using the laser fusion process,” explained Dr Mackoit.
In this experiment, she revealed 192 lasers with very high power and short pulse durations were aimed at a one-millimetre target consisting of a fuel capsule containing hydrogen isotopes, deuterium and tritium. When the laser heated up the central point, a fusion reaction occurred, resulting in deuterium and tritium fusion. When fused, each pair of hydrogen isotopes created a helium nucleus, which was stable enough to release a relatively large amount of energy. The result of this experiment was that, for the first time, the energy produced was more significant than the energy used to initiate the process.
Commercial success is far away
“However, the lasers used in the experiment consumed 300 megajoules of energy. This means that no account was taken of the energy losses that occurred due to the laser radiation. It will therefore be necessary to extract even more energy to convert this energy into a form that can be supplied by the electricity grid, which will require both a large number of fuel capsules and a lot of time,” said the VU researcher.
Dr Andrius Juodagalvis, a Senior Research Fellow in the Faculty of Physics at Vilnius University, explained the amount of energy that was obtained in the experiment as follows: “If we take 1 litre of water at 20 degrees Celsius and we want to heat it to a boiling point, we will need about 0.335 megajoules of energy. An electric kettle can be only 80% efficient, so it takes about 0.42 megajoules of energy to bring the water to boil. However, the energy from a single capsule could be used to boil 2.5 litres of water if the extraction efficiency were 100%.
According to the speaker, the energy extraction from a single fuel capsule in the form announced by the researchers still needs to be commercialised with the extraction of large amounts of electricity.
“To extract the energy in an industrial (i.e. commercially viable) way, all the costs must be factored in. During the experiment, lasers that consumed a lot of electricity had to be activated in order to make the fusion process work. A capsule of the liquefied (cooled) gas mixture was also used, and the cooling again required energy. Tritium, an expensive material, was used in the experiment, and the capsule had to be manufactured,” said Dr Juodagalvis.
He added that we should also consider the processes whereby the energy released is converted into heat. In a conventional nuclear reactor, the heat generated by nuclear fission is used to heat a heat transfer fluid, such as water, so that steam drives the turbines to generate electricity. Moreover, in every energy conversion, the efficiency of the process has to be taken into account – for example, the thermal energy of the steam is not only converted into the rotation of the turbines but also heats the turbines themselves. At the same time, some of the heat is also wasted simply by cooling the coolant so that it can be used
What does the future hold, and how is the moon involved?
While fusion is a promising way to generate energy, the technological aspects of fusion pose a range of challenges. In addition to those mentioned above, the reserves of tritium used in nuclear fusion are dwindling. Although deuterium is abundant in seawater, tritium is scarce in the planet’s crust. The cost of these elements is also radically different: tritium is available for around USD 30,000 per gram, while the price of deuterium is USD 13 per gram.
Therefore, physicists are focused on ways to produce this material. On the other hand, the helium isotope helium-3 (He3) is found relatively frequently on the moon's surface. Therefore, if the infrastructure for human travel to the moon can be put in place, physicists like to joke that the first business of the people settling there will be extracting and supplying the fuel needed for nuclear fusion.
Looking to the immediate future and the developments in Europe, the International Thermonuclear Experimental Reactor (ITER) is nearing completion in southern France. Among the design challenges for the ITER were ensuring the stability of the plasma, minimising the loss of plasma during its operation, as well as controlling this material in the event of instability since an eruption of the plasma could damage the vessel in which it is contained.
