WASHINGTON: US scientists said on Wednesday they have taken an important step in the long journey toward nuclear fusion -- the very process that powers stars as a viable energy source for humankind.
Using the world's largest laser, the researchers coaxed fusion fuel for the first time to heat themselves beyond the heat they zapped into it, achieving a phenomenon called a burning plasma that marked a stride toward self-sustaining fusion energy.
The energy produced was modest - about the equivalent of nine nine-volt batteries of the kind that power smoke detectors and other small devices. Although the researchers cautioned that years of more work are needed, the experiments at a Lawrence Livermore National Laboratory facility in California were a milestone in the decades-long quest to harness fusion energy.
The experiments produced the self-heating of matter in a plasma state through nuclear fusion, which is the combining of atomic nuclei to release energy. Plasma is one of the different states of matter, along solid, liquid and gas.
The fusion is starting to become self-sustaining, which is a good analogy for a burning plasma, according to Zylstra.
The scientists directed 192 laser beams at a small target containing a capsule less than a tenth of an inch about 2 mm in diameter filled with fusion fuel consisting of a plasma of deuterium and tritium two isotopes or forms of hydrogen.
At very high temperatures, the nucleus of deuterium and the nucleus of tritium fuse, a neutron and a positively charged particle called an alpha particle - consisting of two protons and two neutrons - emerge, and energy is released.
Fusion requires hot fuel in order to burn like a regular fire, but for fusion we need about a hundred million degrees Fahrenheit for decades, but this isn't good enough to produce net energy from fusion, Zylstra said.
Fusion is starting to dominate over the heating we did, because for the first time fusion reactions occur in the fuel provided most of the heating. This is a new regime called a burning plasma, according to Zylstra.
Unlike burning fossil fuels and the fission process of existing nuclear power plants, fusion offers the possibility of abundant energy without pollution, radioactive waste or greenhouse gases. Nuclear fission energy comes from splitting atoms. Fusion energy comes from combining atoms together, just like inside stars, including our sun.
Hundreds of companies and institutions are pursuing a fusion energy future, with some oil companies investing.
Annie Kritcher of Lawrence Livermore National Laboratory, lead designer for the experiments conducted in 2020 and 2021 at the National Ignition Facility, and the first author of a companion paper published in Nature Physics, said Fusion energy is the holy grail of clean limitless energy.
The process of fusion produced about 10 times as much energy as it went into heating the fuel, but less than 10 per cent of the total amount of laser energy is inefficient, according to Zylstra. Kritcher said the laser was used for only about 10 billionths of a second in each experiment, with fusion production lasting 100 trillionths of a second.
Zylstra said he is encouraged by the progress.
Zylstra said that Fusion is an enormously complex technological challenge, and it will require serious investment and innovation to make it practical and economical. I view fusion as a decadal challenge to be a viable source of energy.