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Nuclear fusion reactor could be producing electricity within a decade 

A tennis court-sized nuclear fusion reactor being developed in the US could be producing electricity within a decade, backers claim.  

The SPARC nuclear fusion reactor, a joint project involving Massachusetts Institute of Technology, is expected to begin construction on June 21 next year and take three or four years until completion.

It is hoped that SPARC will demonstrate energy gain from fusion for the first time in history by 2025, and be producing fusion energy to generate electricity to power nearby cities within 10 years. 

Nuclear fusion power works by colliding heavy hydrogen atoms to form helium, releasing vast amounts of energy, mimicking the process that occurs naturally in the centre of stars like our Sun. 

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SPARC, which is on track to begin construction in 2021 and demonstrate net energy gain from fusion for the first time in history by 2025. Pictured, artists' impression of the reactor with a human for scale

Fusion could eventually combat climate change by replacing energy sources that emit greenhouse gases, such as coal and gas. 

Fusion also provides cheap, clean and safe energy without radioactive waste, or the risk of meltdown. 

SPARC will pave the way for the first commercially viable fusion power plant, called ARC. 

MIT said limitations imposed by the Covid-19 pandemic have only slightly slowed progress on SPARC and researchers are back in the labs under new operating guidelines. 

'The work is progressing smoothly and on track,' said MIT, which is working with Cambridge, Massachusetts-based company Commonwealth Fusion Systems (CFS) on SPARC. 

A fusion power plant could provide clean, carbon-free energy with an essentially unlimited fuel supply. From the point of view of electrical power generation, the fusion device is just another heat source that could be used in a conventional thermal conversion cycle. 

'No unexpected impediments or surprises have shown up, and the remaining challenges appear to be manageable,' it said in a statement.  

SPARC is set to be the first experimental device ever to achieve a 'burning plasma' – a self-sustaining fusion reaction in which different isotopes of the element hydrogen fuse together to form helium, without the need for any further input of energy. 

When deuterium and tritium nuclei – which can be found in hydrogen – fuse, they form a helium nucleus, a neutron and a lot of energy.

This is done by heating the fuel to temperatures in excess of 270,000,000°F (150,000,000°C) and forming a hot plasma – a gaseous soup of subatomic particles – held in place by magnets.

The strong magnetic fields are used to keep the plasma away from the reactor's walls, so that it doesn't cool down and lose its energy potential.

Fusion power works by colliding heavy hydrogen atoms to form helium - releasing vast amounts of energy in the process, as occurs naturally in the centre of stars

These fields are produced by superconducting coils surrounding the vessel and by an electrical current driven through the plasma.    

Information gathered from the behaviour of burning plasma is 'crucial' for developing the next step – a working prototype of a practical, power-generating power plant, the SPARC team said. 

Once this is up and running, key information can be gained that will help pave the way to commercial, power-producing fusion devices. 

Fuel running these devices – the hydrogen isotopes deuterium and tritium – can be made available in virtually limitless supplies. 

Work on the first stage of the SPARC project is the development of the superconducting magnets that would allow smaller fusion systems to be built. 

Fusion power plants are set to reduce greenhouse gas emissions from the power-generation sector, which is one of the major sources of these emissions globally.    

SPARC is designed to achieve what is called a Q factor – a key parameter denoting the efficiency of a fusion plasma – of at least two.

This essentially means that twice as much fusion energy is produced as the amount of energy pumped in to generate the reaction. 

Fusion joins two light elements (with a low atomic mass number), forming a heavier element, to generate energy. Pictured, artist's illustration (stock image)

If realised, SPARC would be the first time a fusion plasma of any kind has produced more energy than it consumed. 

Computer calculations and simulation tools show SPARC could actually achieve a Q ratio of 10 or more, MIT claims.

Together, the papers outline the theoretical and empirical physics basis for the new fusion system before it starts construction next year. 

'The MIT group is pursuing a very compelling approach to fusion energy,' said Chris Hegna, a professor of engineering physics at the University of Wisconsin at Madison, who was not connected to this work. 

'They realised the emergence of high-temperature superconducting technology enables a high magnetic field approach to producing net energy gain from a magnetic confinement system. 

Pictured, one of two 800-tonne vacuum vessel assembly tools, as captured by the artist Luca Zanier, involved in the construction of the much larger ITER Tokamak reactor now being built in France

'This work is a potential game-changer for the international fusion program​.' 

The SPARC design would achieve fusion performance comparable to that expected in the much larger ITER Tokamak now being built in France. 

The Provence-based ITER project is expected to begin delivering power in 2035 – several years later than SPARC if all goes to plan for the US team. 

'We’re really focused on how you can get to fusion power as quickly as possible,' CFS CEO Bob Mumgaard told the New York Times.

SPARC would be far smaller than ITER – about the size of a tennis court, compared with a soccer field, Mumgaard said. 

High power in a small size is made possible by advances in superconducting magnets that allow for a much stronger magnetic field to confine the hot plasma, MIT said. 

DIFFERENCE BETWEEN NUCLEAR FUSION AND NUCLEAR FISSION 

 Both are nuclear processes, in that they involve nuclear forces to change the nucleus of atoms.

Fusion joins two light elements (with a low atomic mass number), forming a heavier element.

For fusion to occur, hydrogen atoms are placed under high heat and pressure until they fuse together.

Meanwhile, fission splits a heavy element (with a high atomic mass number) into fragments.

In both cases, energy is freed because the mass of the remaining nucleus is smaller than the mass of the reacting nuclei.

The reason why opposite processes release energy can be understood by examining the binding energy per nucleon curve. Both fusion and fission reactions shift the size of the reactant nuclei towards higher bounded nuclei.

Source: International Atomic Energy Agency  

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