Understanding the fusion energy breakthrough announced by US scientists

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The nuclear energy currently in use across the world comes from the fission process, in which the nucleus of a heavier element is split into those of lighter elements in a controlled manner. In fusion, nuclei of two lighter elements are made to fuse together to form the nucleus of a heavier atom.

ITER’s ‘tokamak’ machine, where the plasma to conduct nuclear fusion experiments is stored. (Image credit: Clement Mahoudeau/AFP)

A large amount of energy is released in both these processes, but substantially more in fusion than fission. For example, the fusion of two nuclei of a heavier isotope of hydrogen, called tritium, produces at least four times as much energy as the fission of a uranium atom which is the normal process of generating electricity in a nuclear reactor. Besides greater energy yield, fusion is also a carbon-free source of energy, and has negligible radiation risks.

But fusion reactions happen only at very high temperatures, 10 times the temperature that exists at the core of the Sun, and creating such an extreme environment in a laboratory requires huge amounts of energy. So far, the energy released in such experimental fusion reactions have been lower than what is consumed to create the enabling high temperatures. At best, some of these reactions have produced ‘near break-even’ energies. That is why the latest experiment conducted at the Lawrence Livermore National Laboratory in California is being considered a big deal.

Fusion still far from reality

Significant though the achievement is, it does little to bring the goal of producing electricity from fusion reactions any closer to reality. By all estimates, use of the fusion process for generating electricity at a commercial scale is still two to three decades away. The technology used in the US experiment might take even longer to get deployed.

Technicians use a service system lift to access the target chamber interior for inspection and maintenance at the National Ignition Facility (NIF), a laser-based inertial confinement fusion research device, at Lawrence Livermore National Laboratory federal research facility in Livermore, California, United States in 2008. Philip Saltonstall/Lawrence Livermore National Laboratory/Handout via REUTERS

There are at least two different ways in which fusion reactions are being experimented with. These differ mainly in the way the input energy is supplied to create the extreme heat to enable fusion, but that also results in differences in design and capabilities. At the Lawrence Livermore facility, scientists use high-energy laser beams to achieve those temperatures, also called ‘inertial fusion’. At some other places, including the international collaborative project in southern France called ITER in which India is a partner, very strong magnetic fields are used for the same purpose.

“It is relatively easier to attain break-even energy levels through inertial fusion compared to magnetic fusion. Obtaining net energy gain is a very important step, but we are still far away from reactor grade fusion reactions. There are many many challenges to be overcome before the potential of fusion reaction is realised,” Dr Indranil Bandyopadhyay, Group Leader, Council Support and Knowledge Management, ITER India, said.

This undated image provided by the National Ignition Facility at the Lawrence Livermore National Laboratory shows the NIF Target Bay in Livermore, California. (Damien Jemison/Lawrence Livermore National Laboratory via AP, File)

According to current timelines, the ITER project is expected to demonstrate the viability of a commercially scalable nuclear fusion reactor between 2035 and 2040. The actual deployment of a fusion reactor for generating electricity could take another decade after that. Several countries, like China, Japan, UK and South Korea, are working on this technology separately as well, apart from collaborating at ITER. Bandopadhyay said it is the magnetic fusion that is expected to deliver the fusion reactors first.

Still, the United States, also a partner at ITER, and some other countries including China, are trying the laser-based inertial fusion as well. This is mainly because this technology can also be used to develop fusion-based nuclear weapons that would be far more powerful and devastating than the current nuclear weapons.

Incremental progress

In December last year, UK-based JET laboratory, which uses magnetic fusion, had improved its own previous record for the amount of energy produced from a fusion reaction. The reaction had run for five seconds and produced 59 megajoules of energy, more than double the previous record.

The fusion reactions currently being run in labs last for barely a few seconds. Those based on laser beams run for even shorter times. It is difficult to sustain such extreme high temperatures for prolonged periods. Bandopadhyay said the ITER project was being designed to run for 3,000 seconds. At its full power, it was expected to produce five times more energy than it would consume. However, when run for shorter time periods, about 300-500 seconds, it could release10 times the energy consumed.

“It is not that there is any physical limit to how long a fusion reactor can run. Magnetic fusion reactions can run for hours. But there are lots of engineering challenges right now,” Bandopadhyay said.

ITER, when operational, would become the biggest machine anywhere in the world, more complex than the Large Hadron Collider at CERN, or the LIGO project to detect gravitational waves. Right now, the ITER reactor is in the machine assembly phase. Over 10 million parts, being manufactured and tested in the seven member countries, have to be transported, assembled and integrated.

India joined the ITER project in 2005. The Institute for Plasma Research in Ahmedabad, a laboratory under the Department of Atomic Energy, is the lead institution from the Indian side participating in the project. As a member country, India is building several components of the ITER reactor, while also carrying out a number of experiments and R&D activities related to the project.