US scientists have made a major breakthrough on nuclear fusion energy. For the first time, scientists have successfully conducted a nuclear fusion reaction resulting in a net energy gain. Researchers at Lawrence Livermore National Laboratory (LLNL), California, the National Laboratory of the US Department of Energy, have achieved this milestone. US Secretary of Energy Jennifer M. Granholm made the announcement on Tuesday, December 13.


As many as 192 high energy lasers were used to achieve the nuclear fusion reaction. The researchers at LLNL heated a capsule of deuterium and tritium, and briefly simulated the reactions taking place in a star, Arati Prabhakar, Science Advisor to the President, said during a press conference Tuesday. She added that this feat pushes towards a "clean energy future".


What is nuclear fusion?


A nuclear fusion reaction is a process in which two light nuclei merge to form a single heavier nucleus, and releases energy because the total mass of the resulting single nucleus is less than the added masses of the two original nuclei. Nuclear fusion reactions, which power the Sun and the stars, could one day serve as a cheap source of electricity. In nuclear fusion, light elements such as hydrogen are fused together to form heavier elements. 


Nuclear fusion releases energy, and scientists at LLNL have achieved a net energy gain for the first time.


Scientists have been trying to achieve nuclear fusion since at least the 1930s. The nuclei of two atoms need to be subjected to extreme heat of over 100 million degrees Celsius in order to achieve nuclear fusion. This will cause the two nuclei to fuse into a new larger atom. The process will release large amounts of energy.


The milestone achieved by US scientists


The major scientific breakthrough was achieved as a result of decades of hard work, and will pave the way for advancements in national defence and the future of clean power. 


On December 5, 2022, a team at LLNL's National Ignition Facility (NIF) reached this milestone by conducting the first controlled fusion experiment in history, DOE said in a statement. The milestone is called scientific energy breakeven, meaning that it produced more energy from fusion than the laser energy used to drive it. 


According to LLNL, 192 laser beams delivered more than two million joules of ultraviolet energy to a tiny fuel pellet to create fusion ignition. 


Fusion ignition refers to the moment when the energy from a controlled fusion reaction exceeds the rate at which X-ray radiation losses and electron conduction cool the implosion (an instance of something collapsing violently inwards). In other words, more energy comes "out" compared to the amount that went "in".


The first-of-its-kind achievement will not only provide new insights into the field of clean fusion energy, but will also help achieve US President Joe Biden's goal of a net-zero carbon economy. 


How the milestone was achieved


The experiment at LLNL surpassed the fusion threshold by delivering 2.05 megajoules of energy to the target, resulting in the production of 3.15 megajoules of fusion energy. For the first time, researchers have demonstrated a most fundamental science basis for inertial fusion energy (IFE), a proposed approach to building a nuclear fusion power plant through inertial confinement fusion at industrial scale. 


Inertial confinement fusion is a process in which a tiny solid pellet of fuel, such as deuterium-tritium, would be compressed to tremendous density and temperature so that fusion power is produced in a few nanoseconds before the pellet blows apart, according to Britannica. In order to achieve the compression, an intense laser beam or a charged particle beam, referred to as the driver, is focused upon the small pellet, which is typically one to 10 millimetres in diameter. 


Several technological developments are needed to achieve affordable and simple IFE to power homes and businesses. 


History of nuclear fusion


In the 1960s, a team of scientists at LLNL, led by physicist John Nuckolls, hypothesised that lasers could be used to induce fusion in a laboratory setting. Their revolutionary idea went on to be known as inertial confinement fusion. 


In order to pursue inertial confinement fusion, researchers at LLNL built a series of increasingly powerful laser systems. This led to the genesis of NIF, the world's largest and most energetic laser system. The size of a sports stadium, NIF uses powerful laser beams to create temperatures and pressures like those in the cores of stars and giant planets, and inside exploding nuclear weapons.


Importance of nuclear fusion


Einstein's famous equation, E=mc² states that mass and energy are interconvertible, and can explain the process of nuclear fusion, according to the DOE. 


While fusion can be carried out using different elements in the periodic table, scientists are especially interested in the deuterium-tritium (DT) fusion reaction because this creates a neutron and a helium nucleus, and generates much more energy than most fusion reactions. Deuterium is a hydrogen isotope with two neutrons, and tritium is a hydrogen isotope with three neutrons. 


The advantages of a DT reaction are that it generates large amounts of energy, and can be conducted at lower temperatures than other elements.


According to the International Atomic Energy Agency, nuclear fusion can generate four times more energy per kilogram of fuel than nuclear fission, a process in which a larger nucleus is split into two smaller nuclei. Nuclear fusion can generate nearly four million times more energy than burning oil or coal. 


Since deuterium can be extracted inexpensively from sea water, and tritium can be produced through the reaction of neutrons generated through fusion with naturally abundant lithium, nuclear fusion will be an environmentally friendly process. Not only is fusion fuel plentiful and easily accessible, but would last for millions of years.


It is believed that future fusion reactors will be intrinsically safe and are not expected to produce high-activity or long-lived nuclear waste. 


Since nuclear fusion is difficult to start and maintain, there is no risk of a runaway reaction. In other words, nuclear fusion can occur only under strict operational conditions. In case of a system failure or an accident, the plasma, which consists of a gas of ions and free electrons, will naturally terminate, lose its energy quickly, and extinguish before the reactor is damaged.


One of the biggest advantages of nuclear fusion is that it does not emit carbon dioxide or other greenhouse gases into the atmosphere.