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Technology. Nuclear fusion could be the way to solve all mankind's energy problems in an environmentally and climate-friendly way for all time. Scientists and engineers have been researching the technology for well over 70 years. Recently they have made enormous progress.

Prometheus once stole the fire from the sun chariot of Helios and brought it to the people. Today, people are sending themselves to use an infinite source of energy, modelled on the sun.

The so-called nuclear fusion has been taking place inside the sun for 4.6 billion years. When the nuclei of hydrogen atoms, called protons, merge in a continuous process, i.e. fuse, an enormous amount of energy is released. What remains is the helium named after the sun god, a completely climate-neutral and completely harmless gas that does not combine with any other element. The fuel hydrogen has another advantage. It is unrivalled in price because it is available in abundance as a component of water. Once the power plant has been built, just a few kilograms of hydrogen will suffice to supply entire cities with electricity for months. For such a fusion to take place, the atomic nuclei must first be freed from the electrons that surround them. In the sun, this happens under high pressure and at temperatures of around 15 million degrees. Since the earth is not subject to such high pressure, ten times higher temperatures of 100 to 150 million degrees Celsius are required here.

As the temperature rises, a plasma is formed, an electrically conductive gas in which the positively charged protons and the negatively charged electrons fly through each other. As the temperature continues to rise, the particles become faster and faster until they finally reach a point where they have enough energy to overcome the mutual repulsion and fuse. Now a multiple of the energy used is released.

However, if only traces of foreign substances, such as dust from the reactor walls, get into such a plasma, it immediately collapses. A merger is no longer taking place. On the one hand, this is positive because a fusion power plant could never explode or get out of control. It would just stop producing energy in the event of a malfunction. On the other hand, it makes the process highly complicated. After all, the plasma must not come into contact with the walls of a reactor.

Avoiding this is probably one of the most difficult tasks physicists and engineers want to solve. If nuclear fusion is to generate energy permanently, the plasma must also be kept in balance permanently. For a long time, fusion was therefore more of a playing field for pure basic researchers. Today, attempts are being made to keep it in a state of suspension with the aid of enormously strong magnetic fields.

At times this works so well that there is now a worldwide race to find out who will succeed first in a reliable permanent fusion and which reactor concept would be best suited for it.

In Germany, researchers are even working on two reactor types, a so-called tokamak called "ASDEX Upgrade" in Garching near Munich and a stellarator type called "Wendelstein 7-X" in Greifswald. Both are operated by the Max Planck Institute for Plasma Physics IPP.

Fusion Wendenstein

The first stellarator was developed in 1951 under great secrecy in Princeton. His plasma vessel looks like a messy twisted bicycle tube with curiously twisted magnetic coils. The great advantage of this crude architecture is that such a reactor can operate continuously. The technically advanced Tokamak, on the other hand, can only generate its energy with interrupted pulses.

Wendelstein 7-X is the largest of 13 stellarators worldwide. In it, the researchers are currently reaching a plasma temperature of 40 million degrees. This would not be enough for a merger in a later power plant. Therefore, Wendelstein 7-X is currently being rebuilt. "The places where the plasma touches the wall of the plasma vessel will in future be protected by water-cooled graphite tiles," explains Isabella Milch, press spokeswoman for IPP. "This allows higher temperatures to be reached and, above all, much longer plasma discharges." The first trials are scheduled to start in two years.

The technically simpler solution is the Tokamak reactor. With about 30 pilot plants worldwide, this type is also the most widespread. It was developed at the Kurtschatow Institute in Moscow in 1952, also under great secrecy. In it, the plasma floats in a torus between strong magnets, usually arranged in a D-shaped circle.

Today, the Tokamak ASDEX Upgrade in Garching is primarily used to search for the best operating modes for plasma. ASDEX Upgrade is the only machine in the world whose plasma vessel is completely lined with tungsten on the inside. The researchers can now investigate whether tungsten interferes with the plasma. This is also a topic for materials research. "For example, IPP has developed compounds of solid tungsten plates and tungsten fibers," explains Milch.

Tungsten is the metal with the highest melting point and therefore actually the ideal candidate for the inner lining of reactor vessels. "But it's also quite brittle originally. The fiber reinforcement makes the material more flexible and break-resistant."

The largest Tokamak in the world is ITER. It has been built in Cadarache in southern France since 2013. If all goes well, around 2025 he will for the first time generate a fusion that, at 500 megawatts for half an hour, will generate ten times more energy than is needed to heat the plasma. Just four grams of hydrogen would be enough for this - a quantum leap.

ITER is a tremendous technical effort by seven nations. Here, researchers and engineers, students and postdocs from India, Japan and Korea work closely together with colleagues from China, Russia, the USA and Europe. In addition, 35 other countries are contributing to the success with experts and component deliveries. After all, 60 percent of the necessary construction work has already been completed.

Member countries do not pay money directly, but provide benefits in kind or components. Organising all this and monitoring the very strict standards requires a very rigid structure and a lot of time. "If ITER had to reach its goal as quickly and cheaply as possible, the project would have been conceived quite differently. We'd probably be there by then," explains press spokeswoman Sabina Griffith.

But ITER is about more than just building a machine that proves that fusion energy is feasible on a grand scale. "The other goal of ITER is to grow a global nuclear fusion industry. Because all components are assembled simultaneously in 35 participating nations, we educate the industry, we educate engineers, we promote young scientists."

In fact, this claim is not insignificant. For despite all the discussion about national climate targets, the problem of global warming can only be solved permanently on a global scale. In this respect, the ITER project points far into the future, especially since the intensive, global cooperation of people from different cultures and across political quarrels can also be the basis for a better and more peaceful world.

The many smaller Tokamak facilities around the world are carrying out detailed research for ITER. Also at the ASDEX upgrade in Garching. "We're investigating plasma scenarios on a small scale for ITER," says Milch. "We are also developing a special neutral particle heating system, heat sensors and pressure gauges for ITER at IPP. And we also participate in the development of the control system."

In the private sector, too, the attempt to grow a global nuclear fusion industry has been successful. Many private companies are now also involved in the race for nuclear fusion. They proclaim to reach their goal faster and to be able to build more compact and cheaper reactors. For example, the young start-up company Commonwealth Fusion Systems (CFS), a spin-off of the elite university MIT, intends to test a new type of magnet in a small reactor that will later be used to construct its own compact and inexpensive fusion reactor. The Lockheed Martin armaments group is also researching a particularly compact model. However, those responsible for most private projects are reluctant to provide detailed information about their technology. It often remains unclear what their progress really is and which of the announcements are used primarily to attract investors.

One of the most distant seems to be the astrophysicist Michl Binderbauer, CEO of the Californian company TAE-Technologies. In the meantime, he talks gladly and in detail about the progress of his "Norman" named reactor, named after his doctoral supervisor Norman Rostoker, the Spiritus Rector behind TAE, who died in 2014.

Fusion TAE

What is special about the TAE reactor is that it uses boron as well as the usual hydrogen for the plasma and the subsequent fusion reaction. This mixture has the advantage that the walls around the plasma do not become weakly radioactive over time as with pure hydrogen. The reactor itself looks like a large, cigar-shaped tube. At both ends plasmas are generated which are then shot at each other.

In this way, the atomic nuclei achieve a particularly high penetration force in the fusion process. "The magnetic fields required for this plasma are therefore weaker, but the plasma is still more stable," explains Binderbauer. "This allows the device to be more compact, and cheaper to manufacture and maintain."

Binderbauer is aware that scientific and technical cooperation is also important for his company. As a partner he won the universities of Princeton and California, the Oak Ridge National Laboratory, about which there is also a cooperation with ITER, as well as the renowned Budger Institute for Nuclear Physics in Novosibirsk. Even Google is there. Its algorithms provide solutions for machine learning and artificial intelligence to evaluate the vast data collection from the numerous measurements.

The steps from a hot plasma to an even hotter plasma and finally to fusion are laborious and tedious because the behaviour of the floating plasma is so difficult to calculate. Artificial intelligence to select and evaluate the data and fast quantum computers for mathematical models of plasmas and fusion could accelerate developments.

To date, investors have invested around 600 million dollars in TAE technology. A new round of financing is scheduled for next autumn. "Above all, we are also looking for strategic partners," says Michl Binderbauer, for example high-tech manufacturer and developer of superconductors, magnets, sensors and electrical circuits. But also partners from the power plant sector or from power stations are in demand.

Such cooperation might enable the scientists to reach their goal more quickly than previously thought. "Norman should reach temperatures of around 35 million degrees this year for 35 milliseconds," hopes Binderbauer. "If we succeed, we are confident that our successor Copernicus will bring us to 100 million degrees." TAE-Technologies would then actually not be far from achieving an energy-generating fusion in ten years' time.

ITER is currently still a research reactor, but the next step is already being planned. It is to be followed by a demonstration plant which, starting in 2048, will show on a small industrial scale and in continuous operation that fusion power plants are in principle suitable for supplying mankind with energy.

It may take even more years until fusion electricity comes out of the socket in infinite quantities and almost free of charge. But the dream is slowly beginning to become reality. ®

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Valuable waste products.

The big issue for all ITER participants at the moment is superconductivity. Conductors made of certain rare metals, but also aluminium or lead, become superconductors at temperatures below minus 260 degrees Celsius. The current flows through them without any resistance and does not get lost.

In the research reactors, these superconductors are needed to generate the strong, constant magnetic fields with the kilometre-long windings of the magnetic coils. Superconducting electromagnets are also being installed in medical devices such as MRTs and CTs. Last but not least, superconductors could one day also replace long, transcontinental copper cables, which today lose a lot of current due to their electrical resistance.

Research is currently underway to realize superconductivity even at higher temperatures in order to reduce the energy required for cooling. Currently, special alloys are used in experiments to create a resistance-free power line at minus 135 degrees Celsius.

The proton gas in the plasma is heated to many millions of degrees according to the principle of kitchen microwaves, but at an enormously high output. Heaters called Gyrotron also improve the production of non-metallic high-tech materials, such as highly resilient sintered glass ceramics. It is used, for example, for cooktops - known as "Ceran".

The tungsten plates developed at the Max Planck Institute for Plasma Physics, reinforced with tungsten fibers, are a new material that is still seeking its application outside fusion research. For example, it could be used for other thermally highly stressed machine parts, for example in engines or in chemical reactions.

TAE-Technologies has also developed an interesting by-product, the spin-off TAE Life Sciences. With the help of his hydrogen-boron technology from reactor research, physicians are testing the use of the so-called boron neutron capture therapy BNCT for the treatment of cancer.

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Can nuclear fusion save the world?

According to scientific consensus, global warming must not rise by more than two degrees if mankind is to be able to manage the consequences halfway - albeit at high cost. For many ecosystems, however, even that will be too much, as the Special Report of the International Panel on Climate Change (IPCC) of October 2018 states. Many of the Earth system's destructive processes are already inexorable, such as rising sea levels, which will be unstoppable for hundreds of years to come.

Nuclear fusion, which is intended to replace all fossil fuels with their CO2 emissions, will therefore come far too late to halt climate change.

For this reason, mankind must continue to rely on renewable energies - solar and wind - as an interim solution. And in doing so, they will probably accept the consumption of resources of various metals and rare earths, which are used for solar cells and windmills and are often produced under inhumane conditions. In the long term, renewable energies will probably not be able to keep pace with mankind's growing demand - for example, the enormous increase in energy consumption for blockchains.

Consistently thought through to the end, today only nuclear fusion has the potential to become the future energy for a completely new world in which people strive for a new balance with nature and the climate. This makes it all the more important to provide much more intellectual and financial resources to drive this technology forward.

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Author: Hanns-J. Neubert

Photos: IPP, Matthias Otte // IPP, Wolfgang Filser // IPP, Thomas Henningsen // TAE

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