Die globale nukleare Bedrohung hat in den letzten Monaten zugenommen, nachdem behauptet wurde, Nordkorea baue Atomwaffen und Präsident Donald Trump drohte dem gefährlichen Führer des Landes. Die eskalierenden Spannungen führten sogar dazu, dass die Weltuntergangsuhr näher auf Mitternacht rückte.
Doch trotz ihres Potenzials, die Welt zu zerstören und unsere Existenz zu bedrohen, hat die Kernenergie auch das Potenzial, den dringenden Energiebedarf des Planeten zu decken.
In den letzten Jahren sind aufgrund technologischer Fortschritte und unseres Verständnisses von Dingen wie Supraleitern zahlreiche Privatunternehmen auf den Forschungszug aufgesprungen. Google hat sich kürzlich mit Kernfusionsexperten zusammengetan, um einen Algorithmus zur Lösung komplexer Energieprobleme zu entwickeln, und das MIT hat kürzlich gesagt, dass die Kernfusion in nur 15 Jahren am Netz sein könnte.
In jüngerer Zeit glauben Wissenschaftler, dass sie eines der Geheimnisse der Kernfusion entschlüsselt haben könnten, indem sie explodierende Sterne betrachteten. Das Team vom Center for Laser Experimental Astrophysical Research der University of Michigan untersuchte, wie Wärme bei der Materialmischung während einer Supernova eine Rolle spielt – dem Lichtpunkt, der entsteht, wenn ein Stern das Ende seines Lebens erreicht und explodiert. Diese Explosionen senden riesige Energiemengen aus, in einigen Fällen mehr, als unsere eigene Sonne im Laufe ihres gesamten Lebens abgeben wird.
Die Rolle, die Wärme bei solchen Fusionsreaktionen im Weltraum spielt, wurde weitgehend übersehen, und Wissenschaftler haben versucht, solche Reaktionen auf der Erde nachzuahmen, um den Durchbruch in der Kernenergie voranzutreiben. Durch das Mischen verschiedener Plasmen mit verschiedenen Elementen, darunter Eisen, Kohlenstoff, Helium und Wasserstoff, unter Laborbedingungen konnten die Forscher feststellen, dass Energieflüsse ein Auf- und Absteigen der Wärme verursachen, was einen erheblichen Einfluss darauf hat, wie sich die Elemente mit dem vermischen Plasmen. Dies wurde in früheren Experimenten so nicht berücksichtigt und könnte endlich den Schlüssel dazu enthalten, die Kernfusion auf der Erde nachhaltiger zu gestalten. Die Forschung wurde in Nature Communications. veröffentlicht
Was ist Kernenergie?
Während Kernkraft das Potenzial hat, Menschen mit nahezu unbegrenzter Energie zu versorgen, beinhaltet die Physik hinter Kernenergie Wechselwirkungen zwischen einigen der kleinsten vorstellbaren Teilchen. Im Zentrum jedes Atoms im Universum befindet sich eine winzige Ansammlung von Protonen und Neutronen, die Kern genannt wird. Die Anzahl der Protonen und Neutronen im Kern bestimmt, welches Element das Atom ist, und der Kern macht den Großteil der Masse dieses Atoms aus.
Innerhalb des Kerns werden die Protonen und Neutronen durch eine der vier fundamentalen Kräfte in der Physik, die als starke Kraft bezeichnet wird, aneinander gebunden. Wie der Name schon sagt, ist die starke Kraft die stärkste von allen vieren, aber sie wirkt nur in kleinen Abständen – wie in einem Atomkern. Die anderen sind gravitativ, elektromagnetisch und schwach. Dieses Video beschreibt die Unterschiede und wie sie sich auf uns auswirken:
Atome sind hauptsächlich leerer Raum. Wenn ein Atom die Größe eines Fußballstadions hätte, wäre der Kern ungefähr so groß wie eine Fliege in seiner Mitte. Der andere Teil eines Atoms sind die Wolkenelektronen, die den Atomkern umkreisen, aber die starke Kraft gilt nicht für Elektronen. Sie werden stattdessen durch elektromagnetische Kräfte gebunden, da sie eine negative Ladung haben, während der Kern positiv geladen ist.
Im Allgemeinen beinhaltet die Kernphysik das Herstellen oder Zerbrechen eines Kerns. Beides sind Prozesse, bei denen ein winziges Stückchen Masse verloren geht und dabei riesige Mengen an Energie freisetzen.
Warum ist Atomkraft so wichtig?
Seit den 1950er Jahren versuchen Physiker, den Prozess nachzuahmen, der die Sonne antreibt, indem sie die Verschmelzung von Wasserstoffatomen zu Helium steuern. The key to harnessing this power is to “confine” ultra-hot balls of hydrogen gas called plasmas until the amount of energy coming out of the fusion reactions equates to more than was put in. This point is what energy experts call “breakeven” and, if it can be achieved, it would represent a technological breakthrough and could provide an unlimited and abundant source of zero-carbon energy.
You’ll likely be aware of Einstein’s most famous equation, E=mc^2. This states that the amount of energy released when a tiny bit of mass is lost is equal to that mass multiplied by the speed of light squared. The speed of light is a pretty huge number.
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The smallest nucleus of any element is made up of just one proton, found in hydrogen atoms. Hydrogen, alongside helium, lithium and beryllium are the lightest elements in the universe meaning not much energy is needed for them to form. These light elements formed at the very start of the universe, when it was around three minutes old and cold enough for protons and neutrons to bind together. This is one reason why hydrogen plasmas are seen as the best source of extracting nuclear energy on Earth.
After these first four elements, the universe hit a wall. More energy was needed for the next 88 elements in the periodic table, in order to overcome the protons repelling each other with their positive charges, and for this nuclear fusion has to come into play.
So what is nuclear fusion?
Almost everything around us was created inside a star. Stars start out with hydrogen, which they squeeze together to form helium. This process continues, releasing energy and heating the star up.
It is this reaction, using hydrogen as a fuel, that scientists and teams like those at TAE Technologies are trying to mimic to achieve nuclear fusion power. When deuterium and tritium nuclei – which can be found in hydrogen – fuse, they form a helium nucleus, a neutron and a lot of energy.
Because nuclear fusion requires huge amounts of energy to get reactions started, the process has proven difficult to copy on Earth. It takes immense pressure and temperatures of around 150 million degrees to get atoms to combine in a fusion reactor.
When a star the size of our sun’s core runs out of hydrogen (its fuel source) it starts to die. The dying star expands into a red giant and starts to produce carbon atoms by fusing helium atoms. Larger stars can create heavier elements, from oxygen to iron, in a further series of nuclear burning. Anything heavier than iron is created in a supernova, the giant explosion at the end of a massive star’s life.
How does nuclear fusion relate to nuclear fission?
Nuclear power, as we know it on Earth, uses a different nuclear reaction, called fission.
When elements start to expand, like uranium or plutonium, with more protons and neutrons packed inside the nucleus, it is possible to break them back down into smaller elements by hitting them with neutrons. This also results in a change in mass, releasing huge amounts of energy.
The problem lies in the so-called “after-products” of the reactions. These substances are highly radioactive, making them incredibly dangerous and this is the most significant downside to nuclear energy.
Radioactive waste has to be handled incredibly carefully and the best way we currently have of getting rid of it is burying it deep underground. But it makes nuclear reactors dangerous places, and disasters in which radioactive waste has been leaked have caused dire consequences, such as the disaster in Chernobyl in 1986 and Fukushima.
Which companies are working on nuclear fusion?
MIT
Working with private firm Commonwealth Fusion Systems, researchers at MIT recently devised a new generation of fusion experiments and power plants using high-temperature superconductors. Although yet to be realised, the partnership is aiming to build a compact device called SPARC.
Once the superconducting electromagnets for SPARC have been developed, expected to be within the next three years, SPARC will use them to generate 100 million watts, or 100 megawatts (MW), of fusion power. While it will not turn that heat into electricity, it will produce “as much power as is used by a small city” – more than twice that used to heat plasma, ultimately creating a positive net energy from fusion for the first time. If successful, this could help create a full-scale prototype of a fusion power plant and put the world on the road to nuclear fusion in just 15 years.
This research follows on from the work being done by Google and TAE Technologies, which calls itself “the world’s largest private fusion company”, and its giant ionised plasma machine C2-U. Google built an algorithm designed to speed up experiments in plasma physics and Tri Alpha Energy’s ultimate aim, similarly to CFS, is to build the first fusion-based commercial power plant. The faster it can complete experiments, the faster and cheaper it can achieve this goal and move the world towards a more sustainable, clean energy source.
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“Increased private sector research into nuclear fusion reflects the huge prize at stake – an abundant, environmentally responsible and safe new way of generating electricity,” Professor Ian Chapman, CEO of the UK Atomic Energy Authority said.
In order to carry out experiments of this kind, the plasma – ultra hot balls of gas – need to be “confined” for long periods of time. TAE Technologies confines these plasmas using a method called field-reversed configuration which is predicted to become more stable as the energy increases, in contrast to other methods where plasmas get harder to control as you heat them.
TAE Technologies’ C-2U pushes these experiments to the limit of how much electrical power can be applied to generate and confine the plasma in such a small space over such a short time. Optimising its settings (the machine has more than 1,000 buttons) and managing the behaviour of plasma is a complex problem and this is where Google’s Optometrist Algorithm comes in.
As Google’s senior staff software engineer Ted Baltz explains, the C-2U machine runs a plasma “shot” every eight minutes and each run involves creating two spinning blobs of plasma inside C-2U’s vacuum. These blobs are smashed together at more than 600,000 miles per hour to create a larger, hotter, spinning ball of plasma.
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The ball of plasma is then hit continuously with particle beams made of neutral hydrogen atoms to keep it spinning. Magnetic fields keep hold of the spinning ball for as long as 10 milliseconds. Google’s algorithm takes all of the parameters from the number of settings to the quality of the vacuum and stability of the electrons to present the human physicists with solutions.
How do nuclear bombs work?
The US was the first country to develop nuclear weapons, followed by Russia in 1949. As of 2016, it is estimated that the US has around 7,000 nuclear warheads, including retired, stored, and deployed weapons. Russia is said to have around 7,300 warheads, France has around 300 and the UK has 215. North Korea, seen as one of the most significant nuclear threats of modern times, has an unknown number of devices, although estimates put the number at around 10.
All nuclear weapons use fission to generate their devastating explosions. Early weapons, including the Little Boy dropped on Hiroshima during WWII, created the critical mass needed to kickstart a fission chain reaction by firing a hollow uranium-235 cylinder at a target made from the same material.
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This technique has advanced in recent years and, in modern-day weapons, the critical mass depends on the density of the material. These weapons detonate chemical explosives around a so-called “pit” of uranium-235 or plutonium-239 metal. These isotopes are the most common elements capable of going through fission. Uranium and plutonium are both found naturally in mineral deposits, albeit in tiny amounts (less than 1% in the case of uranium and even less for plutonium) meaning they need to be “manufactured”. This is a costly and time-consuming process and is the main barrier to building nuclear bombs more freely.
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In modern nuclear explosions, the blast blows inwards, forcing the atoms in the “pit” together. Once critical mass is achieved, neutrons are used to create a fission chain reaction which, in turns, creates the atomic explosion. Thermonuclear fusion weapons use the energy from the fission explosion to force hydrogen isotopes together creating a fireball that approaches temperatures as hot as the sun.