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Scientists at the Oxfordshire-based Joint European Torus (JET) laboratory made a significant breakthrough yesterday in their mission to harness the power of nuclear fusion - the energy that powers the stars.

So what is nuclear fusion?
Fusion works by forcing atomic nuclei together.  This is a process that happens in the core of our Sun, where enormous gravitational pressure enables fusion at temperatures of 10 million degrees Centigrade.  Here on Earth, we can’t reproduce the pressures of the Sun, so we need much higher temperatures to produce fusion.  
There are no materials on Earth that can survive that kind of heat, so scientists have had to come up with an amazing solution.  They create a doughnut-shaped magnetic field to contain a super-heated gas, or plasma.  Inside JET, the plasma gets heated to 150 million degrees C - ten times hotter than the Sun!  This extreme heat means that atomic nuclei can fuse together to form new elements and release vast amounts of energy.

What fuel is used for nuclear fusion?
At JET, the fuel is based on two isotopes of hydrogen - deuterium and tritium - which can combine to form helium.  A larger fusion project, Iter, is being built in the south of France and is set to start using deuterium and tritium to create energy from 2035 onwards.
Deuterium is easily available from seawater, but tritium is very rare.  Iter, and other future fusion plants will make their own tritium by using the high-energy neutrons released when deuterium and tritium fuse to split lithium into tritium and helium.

How much energy was produced at JET?
The five seconds of successful fusion at JET produced 59 megajoules of energy, which is about the same as 14kg of TNT.  This was more than double the previous record of 21.7 megajoules, which was set at JET in 1997.  The average fusion power of 11 megawatts (Megajoules per second) for the five second burst of energy is enough to run a domestic kettle continuously for around 11 hours.

Why is nuclear fusion so important?
Fusion energy could provide a solution to a zero-carbon future.  It releases no greenhouse gases and is incredibly efficient, with 1kg of fusion fuel able to produce energy which is the equivalent of 10 million tonnes of coal.

Why might fusion be better than fission?
Today’s nuclear power stations use the energy produced by splitting the heavy nucleus of the atom of an element like uranium or plutonium into two lighter nuclei.  During the process, a large amount of energy is released, several neutrons are emitted and radioactive products are made.  The neutrons that are released can cause fission in a nearby fissionable material, releasing more neutrons and repeating the process in a chain reaction, during which a large number of nuclei undergo fission, producing large amounts of energy.
Fission is controlled in a nuclear reactor, so that the energy produced can be used to heat water and the resulting superheated steam is used to power generators, which produce electricity.  Uncontrolled fission results in a enormous explosion, as with a nuclear bomb. 
Whilst nuclear fission does not produce greenhouse gases in creating energy for us to use, its radioactive byproducts remain deadly for thousands of years and need to be stored very carefully.  Fusion does not produce radioactive byproducts.  The method used by JET and Iter just produces helium gas, so it’s potentially a much cleaner fuel for the future.

What are the next steps?
If all goes well with the development of Iter, a new demonstration power plant will be built in Europe.  This will be hooked up to the grid and will be designed to produce more electricity than it uses.

What has been said about JET’s achievements?
Dr Mark Wenman, a reader in nuclear materials at Imperial College London said, “Five seconds doesn’t sound like much, but if you can burn it for five seconds, presumably you could keep it stable and keep it burning for many minutes, hours, or days, which is what you are going to need for a proper fusion power plant. It’s the proof of that concept that they have achieved,”

Meanwhile, Professor Ian Chapman, chief executive of the UK’s Atomic Energy Authority said, “It’s clear we must make significant changes to address the effects of climate change, and fusion offers so much potential.”

Photo:  High Energy Particles Flow Through A Tokamak Or Doughnut-Shaped Device - 170922264 © Dani3315 | Dreamstime.com

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