Fusion power: A possible solution to the world’s energy crisis?

By Anita Nandi
 

What powers the Sun? How is it so hot and bright? The centre of the Sun consists of mainly hydrogen and helium at roughly 16 million degrees Kelvin! Hydrogen and helium cannot exist as whole atoms at such high temperatures, instead the centre, or nucleus, of the atom is completely separated from the surrounding electrons. This state is known as plasma. All nuclei are positively charged due to the protons they contain, so two nuclei repel each other more and more as they come closer together, just like two magnets. However, if the nuclei manage to get close enough, another force takes over, which is strongly attractive (imaginatively named the strong force). Deuterium nuclei (hydrogen nuclei with an extra neutron) at extremely high temperatures in the centre of the Sun have enough energy to overcome the repulsion and get close enough for the strong force to fuse the two nuclei together forming one helium nucleus. This process is called nuclear fusion and releases a lot of energy. Fusion is constantly occurring in the Sun producing huge amounts of energy, which is what provides the Earth with the light and heat essential for life.

Our planet and people currently have an energy problem. Half of the UK energy consumption comes from burning coal and gas, which has a disastrous effect on our planet as well as being a finite resource, a quarter comes from nuclear fission processes producing radioactive waste that we do not know how to deal with, and only a quarter from renewable energy. On top of that the global population and energy consumption continues to increase. Suppose we could create conditions similar to those in the Sun here on Earth; we could use the huge amounts of energy released from the process of nuclear fusion to generate our electricity. A fusion power plant would produce a similar amount of power to an average conventional fossil fuel power station, however one kilogram of fusion fuel could provide the same amount of energy as 10 million kilograms of fossil fuel. Also, the waste product of fusion is helium, which is completely harmless.

A lot of work has gone into developing energy generation from nuclear fusion, beginning as early as the 1940s. A key problem is reaching and maintaining such extreme conditions, ten times hotter than the centre of the Sun. How do you keep the plasma contained? It would destroy anything it came into contact with and immediately cool. The solution – the tokamak, a taurus-shaped device (like a doughnut), invented in the mid-1960s in Russia, is the most highly developed fusion reactor. The tokamak uses the fact that charged particles change direction in a magnetic field by strategically arranging powerful magnetic fields to control the ionised plasma within a central region, avoiding contact with the walls of the reactor. An alternative fusion reaction method, developed in the 1960s, involves compressing fusion fuel to extremely high density and temperature using focused high power laser beams. Currently, the world’s largest operational fusion experiment, JET in the UK, uses a 3 meter wide tokamak. It is a European collaboration producing world leading research into fusion reaction conditions and reactor design, paving the way for fusion as a form of energy generation.

Nuclear fusion sounds amazing and so much research is going into developing this technology, so why can we not produce fusion energy yet? Containing this highly energetic plasma is not so easy as particles may occasionally escape the magnetic field and collide with the reactor walls, which could cause a lot of damage, shortening the lifetime of the reactor. Therefore, it is necessary improve the magnetic confinement, as well as ensuring the material used can survive the intense bombardment. Another important problem sounds obvious – the fusion energy produced must be greater than the energy put in – but this turns out to not be so simple in practice. The ratio of fusion energy generated compared to energy put into the plasma was 10-7 in 1965 increasing to roughly 1 (breaking even) today, so while we have come a long way, improvements still need to be made. Other technological difficulties include scaling up the reactor, optimising the efficiency and cost of the fusion process, efficiently harnessing the energy produced and effectively controlling the reactions. Alternative fusion reactor designs and confinement methods are also being investigated alongside the tokamak.

Progress is continually being made towards electricity generation from fusion energy. The International Thermonuclear Experimental Reactor (ITER) in Southern France is being constructed to study nuclear fusion and is expected to start experiments in 2025. It uses the tokamak design and plans to be about 10 times larger than the current largest fusion reactor and produce 10 times more energy than is injected into the plasma. The planned successor of ITER, called DEMO, is expected to be the first fusion reactor to generate electricity, leading to full-scale fusion power stations. In December 2017, the UK government invested £86 million in fusion research at the Culham Centre for Fusion Energy, home to JET, the world’s largest fusion reactor experiment. There are roughly 100 different fusion experiments worldwide, mainly across Europe, US and Asia. Even technology companies from the private sector, such as Google, are beginning to get interested in the prospects of fusion, collaborating with plasma physicists to develop computing techniques for speeding up plasma experiments. With all this interest, are we close to solving our energy problems, or will fusion continue to be just out of reach?

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