US physicists have managed to make a controlled nuclear fusion reaction in a laboratory produce more energy than was used to start it. The breakthrough, achieved at the Lawrence Livermore National Laboratory in California, marks a milestone on the long road to turning nuclear fusion into a clean and potentially inexhaustible source of energy.
Although the experiment demonstrates for the first time the feasibility of producing energy by nuclear fusion on Earth, it does not solve the technical problems of how to produce it on a large scale.
“It is a milestone merger that will go down in the history books,” Jennifer Granholm, US Secretary of Energy, declared at a press conference.
In nuclear fusion, which is the energy that powers the Sun, the nuclei of small atoms come together to form larger nuclei. In this case, nuclei of two isotopes of hydrogen (deuterium and tritium) have joined to form one of helium. The reason energy is released is that the mass of helium is less than that of deuterium and tritium combined. Therefore, the excess mass is converted into energy obeying Einstein’s famous equation: E = mc2.
As a source of energy, nuclear fusion has the great advantage that it does not generate waste that aggravates climate change like fossil fuels or radioactive waste like conventional nuclear power. Furthermore, since hydrogen is a component of water and an abundant element in the sea, it could be a cheap and inexhaustible source of energy.
But it has the disadvantage that it is necessary to reach temperatures similar to those of the interior of the Sun in a controlled manner to initiate the fusion reaction, which had been impossible until now.
This feat has been accomplished at the US Lawrence Livermore National Laboratory’s National Ignition Facility (NIF) by firing 192 high-energy lasers at a small sphere containing hydrogen isotopes. With this technique, called inertial confinement, the sphere is made to implode and a high enough density and temperature are reached to initiate fusion.
The European ITER nuclear fusion project, by contrast, is based on the magnetic confinement technique, which uses magnets instead of lasers to compress hydrogen isotopes.
According to the results presented today, the energy produced in the fusion reaction has been 50% higher than the energy applied by the lasers to initiate it. In theory, the energy gain could be used to keep the fusion reaction going and continue to produce energy, which in turn could be used to produce electricity.
However, some 500 MJ of energy had to be used to activate the lasers and get them to apply 2 MJ to the fusion reaction. Therefore, the energy produced with the fusion does not compensate for the total energy used in the experiment.
In addition, for nuclear fusion to become a large-scale energy source, it must be produced in a sustained manner over long periods, which will require the development of new technologies to gradually supply hydrogen isotopes to fusion reactors.
Even so, the announcement that for the first time there has been an energy gain in a nuclear fusion reaction has been enthusiastically received among physicists working in this field.
“It is a great scientific milestone,” says Carlos Hidalgo, from the Center for Energy, Environmental and Technological Research (CIEMAT), in statements made on Monday to the Science Media Center. “The practical achievement of nuclear fusion energy is one of the great challenges of humanity in the 21st century.”
According to Gianluca Gregori of the University of Oxford, “although this is not yet a viable power plant, the path for the future is much clearer.”
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