I was recently captivated by the sheer scale of a new technology. On the horizon is the promise of something way bigger than renewable energy – nuclear fusion – with the vision of a clean and endless source of fuel.
In fusion, the nuclei of hydrogen isotopes are forced together, liberating a massive amount of light and heat. The idea is to take hydrogen gas, superheat it to more than 100 million degrees Kelvin – hotter than the sun – until it forms a plasma, and then compress it with powerful magnets to force the hydrogen isotopes together, producing helium and high speed neutrons. The energy released is harnessed to heat water, create steam and spin a turbine, producing electricity. In fact we experience this every day; the sun and stars are giant self-sustaining fusion reactors where huge gravitational forces compress matter, forcing atoms to fuse, and generating vast amounts of energy.
This is the opposite of the nuclear fission that we all know, which breaks atoms apart. Fission is expensive, it generates dangerous radioactive waste, and it raises serious issues about safety and the threat of nuclear weapons. On the other hand, fusion doesn’t produce greenhouse gases or generate radioactive pollutants. And the fuel for fusion, hydrogen, is plentiful enough to meet our energy needs for millions of years.
A plasma is an ionised gas. At extreme temperatures, electrons are separated from their nuclei and move freely about. Composed of charged particles – positive nuclei and electrons – a plasma is nearly a million times less dense than air.
The beams used to heat the plasma must be neutral so they are not deflected by the magnetic field. So deuterium ions are energised by passing them through a series of high voltage grids. The ion beam is then converted into neutral atoms by passing it through deuterium gas, where the ions pick up electrons. The beams of neutral atoms then penetrate deep inside the plasma, where they become re-ionised. They are trapped inside the magnetic field and heat the plasma by colliding with its ions.
Huge challenges
Fusion is incredibly difficult, and commercial scale fusion is an engineering challenge rather than a scientific one. The reactor needs to be built out of material that can stand up to the intense heat of the plasma, which has to be kept at extremely high temperatures under massive pressure. It’s a colossal undertaking and an enormous amount of energy is needed.
However, things are happening. Over 35 countries have embarked on a major international cooperative effort called Iter. The Iter fusion reactor in France is 70% built and is expected to achieve its first plasma in 2025. It incorporates a doughnut shaped vacuum chamber called a tokamak, based on a Russian design, which confines the plasma in a doughnut-shaped torus. This will be a fully working demonstration reactor, providing 500 megawatts of fusion power – about the production of an average coal-fired plant, and 140 times greater than the output of a wind turbine.
In another project, the UK aims to build a commercially viable fusion power plant by 2040. The Step reactor will use a spherical tokamak design like an apple core, which is more compact. This means that the magnets can be much smaller, potentially saving millions.
A major advance that makes Step viable is its Super-X divertor. Plasma exhaust is one of the biggest technical challenges. The heat generated by fusion has to go somewhere. Otherwise the vessel’s walls would instantly melt. By-products and excess heat from the plasma need to be removed. So the plasma exhaust is directed towards an exhaust system known as a divertor. The Step project aims to reduce the heat to manageable levels on a par with those found in a car engine.
One possibility is to use part of an existing power plant, with the old power generation system replaced with the new Step reactor. The benefit of this is that the energy conversion process for creating electricity remains the same. Utilising a site with an existing turbine building makes the project a lot more feasible.
It’s when, not if
What’s exciting is the private companies. They are smaller and nimbler, and they develop by making mistakes and learning fast. There are dozens of them around the world, raising funds and bringing different approaches – just as there are in the space race. Just last month came the news that Jeff Bezos is retiring from Amazon and taking on Elon Musk’s SpaceX.
Looking at what mankind has achieved over time when down to the wire, I am thinking that maybe nuclear fusion is going to be the next giant leap.
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