power the sun 4.Technology Nuclear 2.Wendelstein Harnessing the FUSION ENERGY

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1 FIREBALL: The sun is a giant ball of red-hot gases. Every year, it radiates 15,000 times more energy onto Earth than the entire global population consumes in the same 12 months. FUSION ENERGY Harnessing the power of the sun At the Max Planck Institute for Plasma Physics in Greifswald, Germany, scientists are researching a new source of energy. They are modeling their work on the process that makes stars shine. Text: Tanja Requardt, Martina Rathke 1. Fusion research The aim is to harness the energy source that powers suns and stars. To do this, scientists are researching nuclear fusion, the physical process that generates energy inside stars. 7-X Greifswald, a city in 2.Wendelstein northeast Germany, is home to one of the largest experimental facilities in the world. The first plasma was produced in the reactor here at the end of Executive Summary ITER project The international fusion 3.The reactor, which is being built in Cadarache in the south of France, is set to perform the first fusion of hydrogen nuclei. The results from Greifswald will play a role in this. 4.Technology Nuclear fusion produces radioactive waste that must be put into interim storage. The half-life of the waste is shorter than that of the waste produced by splitting atoms in nuclear power plants. Photos: Shutterstock 28 GASWINNER GASWINNER 29

2 FUSION ENERGY / RESEARCH NUCLEAR FUSION: Researchers are taking their cue from the nuclearphysical processes that occur inside stars and make them shine (top right). CONTROL ROOM: At the Institute for Plasma Physics in Greifswald, physicists watch over the Wendelstein 7-X nuclear fusion device, in which very hot plasma is generated (top left). WENDELSTEIN 7-X: As the experiment currently stands, visitors to the facility, which is located behind a wall 1.8 metres thick, are only required to wear a helmet. There is no need for any protection from radioactivity (bottom). Photos: Michael Jungbluth (2), IPP Concentration and anticipation are high in the control room at the Max Planck Institute for Plasma Physics in Greifswald. Now we want to reach 500 milliseconds, says physicist Dirk Naujoks, announcing the next discharge over the microphone as he navigates, pilot-like, through the experiments at the Wendelstein 7-X nuclear fusion device. Around 70 researchers from Germany, Spain, Poland, Hungary, and the United States are glued to the monitors in the control room. The plasma flares up brightly for just a moment. Measured data from the inside of the device are transformed into curved diagrams at lightning-quick speed. The experiment was a success it produced a plasma with a temperature of several million degrees. Given the dwindling reserves of fossil fuels and the everincreasing demand for energy, it is crucial that we tap into new sources of energy, says Naujoks. Indeed, according to various scenarios and depending on worldwide population growth, global energy consumption in 2100 is expected to be some three to six times higher than it is now. The BP Energy Outlook expects a 34 percent rise in energy demand by 2035, based on a global population of 8.8 billion and on economic growth, particularly in newly industrialized countries. So how can we meet this enormous demand? Some 400 physicists and engineers in Greifswald are working on one answer to that question. We want to find a new primary energy source for humanity, says Professor Thomas Klinger, scientific director of the Wendelstein 7-X project. To achieve this goal, he and his team are researching the physics of hot plasmas. Plasmas are extremely thin, hot gases made up of ions and electrons. Plasma occurs when you heat gas. The idea is that a future power plant would use extremely high temperatures to fuse hydrogen ions or nuclei, says Klinger. The technology is being modelled on nuclear fusion, the process that generates energy inside the sun and the stars and makes them shine. GOAL WITHIN REACH The Wendelstein 7-X (which weighs 725 tonnes and has a diameter of 16 metres) cannot recreate conditions quite as extreme as those found inside stars. Nevertheless, temperatures in It is crucial that we tap into new sources of energy excess of 150 million degrees create scope for investigating hot hydrogen plasma in fusion power plants. The Wendelstein 7-X will not produce the kinds of fusion reactions planned for power plants. The idea is that a future power plant will fuse hydrogen nuclei to form helium in a process that releases neutrons and large quantities of energy. One kilogram of hydrogen fused to helium produces as much energy as burning 11,000 tonnes of hard coal, says Klinger. Researchers, physicists, and engineers have been working with plasma, a state of matter, since as long ago as the 1950s. Experts now want to find out how to disconnect the energy created by fusion from the hot plasma and make it available for use. We re within reach of the goal, says Klinger. After more than 15 years of preparation ten of which were the construction phase the Wendelstein 7-X went into operation in December of German chancellor Angela Merkel visited the 1 billion research facility this February and gave the starting signal for the first hydrogen plasma. RADIOACTIVE WASTE On the road to a fusion power plant, the Greifswald experiment is an important step. The fusion researchers believe that nuclear fusion which is capable of producing base-load power and is free of harmful carbon emissions could replace nuclear fission as a lower risk alternative in the second half of the 21st century. Fusion power plants have a number of advantages over plants that run on nuclear fission. The fuels are said to be basically inexhaustible and from a purely physical perspective a nuclear disaster is impossible. A fusion reactor also does not produce highly radioactive nuclear waste. That said, the process is not entirely safe after all, a fusion power plant produces energy by fusing atomic nuclei. Radioactive waste occurs in the form of the reactor material, which must go into interim storage once the plant stops operating. After a decay time of between 100 and 500 years, the risk potential of the radiotoxic content is comparable to that posed by the radioactive material that all the ash produced by a coal-fired power plant of the same size naturally contains, explains Klinger. Fusion researchers are now focusing on two concepts for the magnetic confinement of plasma, which in a future power plant will be made from a mixture of the isotopes deuterium and tritium. One concept is the stellarator, which was developed in the United GASWINNER 31

3 RESEARCH MODULE: The stellarator is a complex ring with plasma and magnetic coils. A fusion power plant based on the Wendelstein 7-X design would have 3 gigawatts of fusion power. FUSION ENERGY / RESEARCH Foto: IPP 32 GASWINNER Did you know that the deuterium present in a bath half-full of water and the lithium from a single laptop battery would be enough to supply a person in Central Europe with electricity for 30 years? Professor Thomas Klinger, Scientific Director, Wendelstein 7-X GASWINNER 33

4 RESEARCH / FUSION ENERGY FUSION ENERGY / RESEARCH Testing nuclear fusion Some 1,000 cryogenic pipes cool the cryostat and supply the coils with liquid helium. A cage of magnetic coils Coils supplied with current generate a magnetic cage for the ideal confinement of the plasma and to insulate it against the material walls. Continuous operation with high currents requires superconducting coils that need to be cooled to around 269 C with liquid helium. The components Within the plasma, up to 30 milligrams of hydrogen are dispersed over 30 cubic metres. Load on the graphite tiles per square metre Construction time W7-X: 10 Space shuttle heat shield on re-entry: 6 Golden Gate Bridge: 4 = one year W7-X: 10 = one megawatt Superlatives It is almost impossible to imagine the conditions under which the experiment occurs. A few comparisons can help provide a better idea of the situation. Heating systems output = one megawatt Reference value The Wendelstein 7-X fusion experiment aims to find out what conditions are needed to allow fusion reactions resembling those that occur in the sun to take place on Earth. The experiment is divided into various phases that will prepare the ground for a future commercial reactor. 254 ports in over 100 different designs for connectors, feed lines, manholes and diagnostic tools pass through the outer vessel and the cryostat (the actively cooled and thermally insulated space between the outer and plasma vessels), and lead directly into the plasma vessel. Magnetic coils The coils are about 3.5 metres high, weigh six tonnes, and are housed in a stainlesssteel casing. Plasma Cross-section of a coil Each coil contains 120 windings of a superconducting cable, through which the current runs that will create the magnetic field. The individual cable windings are fixed in a matrix in a stable coil casing made of steel. The stainless-steel plasma vessel matches the shape of the plasma. Fifty superconducting magnetic coils, each weighing six tonnes, create the 3-tesla magnetic field to contain the plasma. Current in the superconducting cables Energy produced from one gram of fuel Total costs Work invested Offshore wind turbine: 6 = 10 million W7-X: 1,060,000,000 = 10,000 hours W7-X: 15 W7-X: 18.5 Energy consumed by 50,000 US households per hour: 63,000 Average working life in Germany: 60,720 = one kiloampere = one kilowatt-hour Value for Wendelstein 7-X Future fusion power plant*: 90,000 Allianz Arena: 340,000,000 Burj Khalifa: approx. 1,000,000,000 Cross section of a superconducting cable W7-X: 1,100,000 4,000 metres of cooling pipes have been installed. They could wrap around the entire reactor almost 80 times. Cavity The liquid helium needed for cooling is fed through 37 percent of the cavity inside the cable loom. 243 copper strands conduct the electricity in a core made from the superconductor niobium-titanium. Twenty additional coils make it possible to influence and change the magnetic field. Plasma temperature = one million degrees Celsius Sun s core: 15,000,000 Total weight = one tonne Surface of the hottest known stars: 100,000,000 W7-X: bis 100,000,000 Max Planck Institute for Plasma Physics The site in Greifswald has space for over 400 people. African elephant: 6 Microwave heating Electricity supply Cooling systems Office buildings Data center Diagnostics hall Laboratory and workshop building Torus hall with Wendelstein 7-X Radio-wave heating 50 m Divertors are the main contact between the hot plasma and the cold wall. They capture a lot of the heat and particle flow and regulate it. Some 6,000 tiles made of graphite cover the plasma vessel and protect it from the extreme heat. The tiles are manufactured individually in the institute s workshops. The fourth state of matter Plasma is made up of positively and negatively charged particles that move independently of one another. In a magnetic field, they are forced to move in spiral paths, which limits their freedom of movement. The final phase at Wendelstein 7-X should confine hot plasma in a predefined magnetic field configuration for up to 30 minutes. Astronomical heat In order to achieve the extremely high temperatures needed for fusing atomic nuclei, three methods are used that can target specific plasma components. Microwave heating plays the main role. Ten gyrotrons produce high-frequency alternating fields whose energy is bundled and conducted via water-cooled mirrors through a 60-metre-long tunnel and into the reactor. Heating methods: Electron heating Microwaves (radar waves) heat the electrons in the plasma. Ion heating Microwaves (radio waves) heat the ions in the plasma. Neutral beam injection Fast, neutral hydrogen beams are shot into the plasma. Grafik: C3 Visual Lab The coils are mounted on a support structure. The outer vessel forms the shell of the reactor. An insulation vacuum separates the outer vessel from the plasma vessel. Airbus A380: 569 *Wendelstein 7-X will not produce any energy W7-X: 725 Blue whale: 190 If this line was inside the reactor the temperature at this point would be 269 degrees Celsius 34 GASWINNER GASWINNER 35 while the temperature at this point, 50 cm further away, would be up to 130 million degrees Celsius.

5 RESEARCH / FUSION ENERGY Nuclear fusion: a safe source of energy? If we can get nuclear fusion to work for us here on Earth, we will have made a substantial contribution to humanity s future energy supply. Beate Kemnitz, Max Planck Institute for Plasma Physics FUSION ENERGY / RESEARCH Fusion vs. fission With both nuclear fusion and nuclear fission, the sum of the masses of the end products is smaller than that of the starting materials. The missing mass is transformed into energy following Einstein s famous equation E=mc². The main advantages of fusion are the type of materials used, the higher level of safety, and the unproblematic end products. Nuclear fusion Nuclear fission Starting materials Deuterium/tritium Uranium/plutonium Occurrence % in water/breeding Mining/breeding Half-life in years ,110 Radioactive waste Yes Yes Type of storage Interim storage Final storage Uncontrolled chain reaction No Yes Producing energy by nuclear fusion The starting materials deuterium and tritium are heated until they form a plasma, which is an extremely hot, thin gas. In this state, they fuse and release energy that, in the form of heat, can drive a steam turbine and thereby generate electrical energy. Proton Neutron Deuterium (heavy hydrogen) Helium 1 Charged nuclei sense an electro-static repulsion (Coulomb barrier) 4 The helium passes its energy on to the plasma particles by colliding with them. Tritium (super-heavy hydrogen) 2 Hot (fast) nuclei 3 overcome the repulsion and fusion occurs. The fusion creates a helium nucleus and a neutron. The mass deficit is transformed into the kinetic energy of the reaction products. 5 The neutron s high kinetic energy is the useful energy that will subsequently be transformed into electricity. Tokamak Developed in 1952, the tokamak was the most promising fusion reactor design for a long time. The outer coils create a magnetic field in the shape of a ring. The strong current flowing inside the plasma allows for dynamic plasma confinement and has achieved considerable plasma heating, even in early experiments. The tokamak design is relatively simple. Stellarator The stellarator is a more complex construction, and earlier reactors failed to confine the plasma as well as the tokamak could. Plasma confinement is achieved solely by the outer coils, and is therefore suited to continuous operation from the outset. Scientists are now hoping that an optimised stellarator could be the right technology for future fusion power plants. Magnetic coils Plasma Grafik: C3 Visual Lab INSIGHT: A still-open Wendelstein 7-X module at the Greifswald Max Planck Institute shows the highly complex construction of the world s most advanced stellarator research facility. GASWINNER 37

6 FUSION ENERGY / RESEARCH NUCLEAR FUSION»New primary energy for the world«professor Thomas Klinger, scientific director of the Wendelstein 7-X experimental facility in Greifswald, talks about the progress of fusion research in Germany and around the world. LARGE-SCALE PROJECT: Over one million hours have been invested in building Wendelstein 7-X over the past ten years. The experimental reactor produced hydrogen plasma for the first time in States in 1951, and the other is the tokamak, which was invented by Soviet physicists. Both designs use coils to create a magnetic field. The difference is that the tokamak plasma has a strong current running through it, while the stellarator plasma is more or less current-free. Because the tokamak is very good at magnetic confinement, it has been more successful at confining hot plasma over the past few years than the more complex stellarator. That said, the tokamak s instabilities have proven risky. Unlike tokamaks, which can only be operated in pulsed mode unless additional measures are taken, stellarator fusion reactors can be operated continuously straight from the off. After around 20 years of research, scientists have finally succeeded in optimising the stellarator s magnetic field. The international team in Greifswald began preparing the optimised stellarator for operation in May Now the researchers want to show that it can produce fusion-relevant, power-plantready plasmas that remain in a steady state for over 30 minutes. When Chancellor Merkel came to Greifswald for the commissioning, the discharge lasted 40 milliseconds at an ion temperature of 14 million degrees. We re at seven seconds now, says Klinger. That means the discharge rate has increased by a factor of almost 150. You have to start slow you can t just go full throttle right away, jokes Klinger. We are researching the magnetic field for a future power plant. superconducting coils in Greifswald delayed the project by several years and increased costs. This led critics of fusion research to raise the volume of their objections. Environmental organizations believe that nuclear fusion is an overly expensive and risky way of producing energy. Fusion researchers, however, are happy to highlight the advantages. In a future energy mix that is dominated by renewables, fusion power plants could supply the 30 percent base load needed to keep the electricity networks stable. The only renewable energy capable of providing base load is hydropower, and that only plays a significant role in a few countries, such as Norway, says Klinger. Still, the speed at which publicly funded basic research gives way to a practicable technology with market-ready power plants will depend on the market. If technology is to reach the stage where it is ready for market, it needs companies to get behind it, says Klinger. This, he explains, will probably happen when fossil fuels get too expensive and it becomes possible to make money with fusion energy. LOCATION Fusion research in Greifswald Mr Klinger, what makes the Wendelstein 7-X project so special? We want to tap into a new primary energy source that is based on the fusion of lightweight hydrogen nuclei. In Greifswald, we are operating the most advanced and along with a facility in Japan biggest stellarator fusion experiment in the world. Germany is not the only country doing fusion research. What is the situation elsewhere? About a dozen large devices exist around the world. Some are in Europe, while others are in Japan, Russia, China, South Korea, India and the United States. All these countries are participating in the flagship ITER project (International Thermonuclear Experimental Reactor). ITER is currently under construction in France. When finished, it will be a complete experimental nuclear fusion reactor. It will use the tokamak design to generate a magnetic field. The long-term goal is to generate electricity from fusion energy. When will it be possible to produce electrical energy from hydrogen fusion? We expect the results from the Wendelstein 7-X and ITER experimental reactors to be available after Then we can decide how to proceed. This is a very significant step on the road to building a power plant. The aim of the European Roadmap is for us to be able to produce energy from hydrogen fusion by the second half of this century. I m optimistic that we can achieve this. Photos: IPP, Michael Jungbluth (2) FUSION POWER CAN SUPPLY BASE LOAD The Wendelstein 7-X experiment is too small to function as a power plant. It is not intended to be used for fusing hydrogen to helium. The idea, though, is to show that the magnetic field geometry can lead to a future power plant, says Klinger. The plan is then for the fusion experiment to be implemented in the large-scale international project ITER (Latin for the way ). ITER is a tokamak nuclear fusion reactor that has been under construction in Cadarache in the south of France since It is expected to go into operation in The aim is to use ITER to generate more energy than is needed to run it. Former French president Jacques Chirac has described the project as the biggest scientific experiment since the International Space Station. The researchers still have a few technical hurdles to clear before the reactor is ready, though. Previously, problems with the three-dimensionally curved The world s largest stellarator fusion reactor is in Greifswald, Germany. The Wendelstein 7-X is in operation at the IPP branch institute (Max Planck Institute for Plasma Physics), which was founded in 1994 in the state of Mecklenburg-Vorpommern. Some 400 researchers work here on an interdisciplinary basis. Fusion-oriented plasma physics links the IPP with the University of Greifswald and TU Berlin. 38 GASWINNER GASWINNER 39