Scientists at the US National Ignition Facility (NIF) in California have successfully produced a nuclear fusion reaction which could pave the way for abundant clean energy in future. According to the researchers, the fusion experiments released more energy than was pumped in by the lab’s enormous, high-powered lasers. This landmark achievement is known as ‘ignition’ or ‘energy gain’.
The technology is far from ready to turn into viable power plants but the breakthrough was hailed as evidence that the power of the stars could be harnessed on the Earth.
Though nuclear fusion and nuclear fission both draw energy from the atom, they operate differently. Present day nuclear power plants rely on nuclear fission which releases energy when large and heavy atoms, such as uranium, break apart due to radioactive decay. However, in nuclear fusion, small light atoms, such as hydrogen, fuse into bigger ones. In this process, they release a small part of their combined mass as energy.
On December 5, 2022, the scientists of the NIF conducted an experiment in which an array of lasers fired 2.05 megajoules (MJ) of energy at a tiny cylinder holding a pellet of frozen deuterium and tritium, which are heavier forms (or isotopes) of hydrogen and got about 3.1 MJ of output—roughly a 50 per cent gain. It is an important step towards the goal of generating almost unlimited power from clean and plentiful fusion energy.
The Experiment
In the NIF method, the researchers used a peppercorn-size pellet of frozen mix of two heavier isotopes of hydrogen, deuterium, and tritium. The capsule was then placed into a one centimetre-long gold cylinder called a ‘hohlraum’ which was then mounted on an arm in the middle of a larger laser-studded chamber.
To trigger fusion, the NIF fired 192 giant lasers all at once at the hohlraum, which were angled into it through two holes. The beams were then slammed into the hohlraum’s inner surface. This caused it to spit out high-energy X-rays that rapidly heated up the outer layers of the capsule to more than 3m degrees Celsius, making them burn off and fly outwards. The inner part of this capsule rapidly compressed to nearly a hundred times denser than lead. This forced the deuterium and tritium inside to reach the temperatures and pressures needed for fusion. The X-rays stripped the surface off the pellet and triggered a rocket-like implosion. Thus, temperatures and pressures reached at extremes which could only be seen inside stars, giant planets, and nuclear detonations. The implosion reached a speed of 400 km per second, causing the deuterium and tritium to fuse and produce energy in less time than it takes for light to travel one inch.
Challenges
Though this breakthrough has been reached by the researchers, there are still many hurdles to make this success a reality and create fusion power plants. Some of them are as follows:
- While the pellet had released more energy than the lasers put in, the calculation did not include the 300 MJ or so needed to power up the lasers in the first place.
- The NIF lasers were operated once a day in the experiment, but a power plant would need to heat targets 10 times per second.
- There exists the cost of the targets. The targets used in the experiments cost tens and thousands of dollars, and for a viable power plant, the cost would be much more.
- Another issue is how to get the energy out as heat.
- It would take decades of research to build a power plant. A fusion reactor power plant would need to generate 50 to 100 times more energy than its lasers emit to cover its own energy use and put power into the grid.
- It would also have to vaporise 10 capsules per second for long periods of time. At present, fuel capsules are extremely expensive to make. Also, these capsules rely on tritium, a short-lived radioactive isotope of hydrogen, which has to be made on-site by the future reactor plants.
However, most of these challenges, not unique only to NIF, are being faced by many fusion labs around the world. In 2021, the Joint European Torus (JET), an experimental reactor in Culham, England, set the record for the most fusion energy ever released during a single experimental run. Furthermore, private companies in the US and UK have built next-generation superconducting magnets which could help create smaller and more powerful reactors.
As per Dr Mark Wenman, a reader in nuclear materials at Imperial College, London, challenges remain of how you can get the energy out of the system; how to sustain the energy for long enough; how to scale up the energy; and whether the energy can be cheap enough to compete with other sources.
Efforts in the UK
A few months earlier to this experiment, a successful fusion experiment was also conducted in the UK in which the scientists used donut-shaped tokamak. Tokamak is a machine that uses magnetic fields to heat hydrogen atoms to extraordinary temperatures in order to create a fusion reaction. Though that experiment could not reach the break-even point in terms of energy output, the results helped validate an approach being pursued by a multi-nation consortium building the larger US$ 22 billion International Thermonuclear Experimental Reactor (ITER) tokamak project in France. This project is expected to create a reaction that could produce ten times more energy as the output.
Conclusion
To conclude, it would be hard to predict whether this work would yield a new energy future. However, fusion researchers see this technology as an incredible tool for mankind. Scientists around the globe are working towards scaling up their fusion projects as well as bringing down its cost of production. According to Einstein’s equation, E=mc2, each fusing pair of hydrogen nuclei would produce a lighter helium nucleus and a burst of energy. Deuterium could easily be extracted from seawater, while tritium could be made from lithium which is found in the Earth’s crust. Getting it commercially viable is a matter of time.
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