Nuclear energy: Exploding stars may hold the key to unlocking nuclear fusion on Earth

The global nuclear threat ramped up in recent months following claims North Korea was building nuclear weapons and president Donald Trump’s threat against the country’s dangerous leader. The escalating tensions even caused the Doomsday Clock to move closer to midnight. 

However, despite its potential to destroy the world, and threaten our very existence, nuclear energy also has the potential to solve the planet’s pressing power needs.

In recent years, swathes of private companies have been jumping into the research bandwagon, due to advances in technology and our understanding of things like superconductors. Google recently teamed up with nuclear fusion experts to develop an algorithm for solving complex energy problems, and MIT has recently said nuclear fusion could be on the grid in just 15 years. 

More recently, scientists believe they may have unlocked one of the mysteries of nuclear fusion by looking at exploding stars. The team, from the University of Michigan’s Center for Laser Experimental Astrophysical Research group, looked into how heat plays a role in the way materials mix during a supernovae – the point of light created when a star reaches the end of its life and explodes. These explosions send out vast amounts of energy, in some case more than our own sun will give out over the course of its entire lifetime. 

The role heat plays in such fusion reactions in space has been largely overlooked and scientists have been attempting to mimic such reactions on Earth to help drive nuclear energy breakthroughs. By mixing different plasmas with various elements including iron, carbon helium, and hydrogen in lab conditions, the researchers have been able to establish that fluxes in energy cause the heat to rise and fall, which has a significant impact on how the elements mix with the plasmas. This has not been considered in this way, in previous experiments, and could finally hold the key to making nuclear fusion more sustainable on Earth. The research is published in Nature Communications. 

What is nuclear energy?

While nuclear power has the potential to provide humans with almost limitless energy, the physics behind nuclear energy involves interactions between some of the tiniest particles imaginable. At the centre of every atom in the universe lies a tiny collection of protons and neutrons called a nucleus. The number of protons and neutrons in the nucleus determines which element the atom is, and the nucleus makes up the majority of that atom’s mass.

Inside the nucleus, the protons and neutrons are bound together by one of the four fundamental forces in physics called the strong force. As its name suggests, the strong force is the strongest of all four, but it only works in small distances – like those inside a nucleus. The others are gravitational, electromagnetic, and weak. This video describes the differences, and how they impact us:

Atoms are mainly empty space. If an atom was the size of a football stadium, the nucleus would be roughly the size of a fly in its middle. The other part of an atom is the cloud electrons orbiting an atom’s nucleus, but the strong force does not apply to electrons. They instead are bound by electromagnetic forces, as they have a negative charge while the nucleus is positively charged.

Generally speaking, nuclear physics involves the making or breaking of a nucleus. Both are processes through which a tiny bit of mass is lost, and these release huge amounts of energy.

Why is nuclear power so important?

Since the 1950s, physicists have been attempting to mimic the process that powers the Sun by controlling the fusion of hydrogen atoms into helium. 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.

 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. 

Google

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. 

READ MORE: What is a hydrogen bomb?

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. 

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