U.S. scientists said on Wednesday that they have taken an important step in the long journey toward making nuclear fusion a viable energy source for humankind.
The researchers coaxed fusion fuel for the first time using the world's largest laser, 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 9 volt batteries of the kind that power smoke detectors and other small devices. The experiments at a Lawrence Livermore National Laboratory facility in California was a milestone in the long-term quest to harness fusion energy, even as the researchers cautioned that years of more work are needed.
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.
If you want to make a camp fire, you want to get the fire to hot enough that the wood can keep itself burning, said Alex Zylstra, an experimental physicist at Lawrence Livermore National Laboratory and lead author of the research published in the journal Nature.
The fusion is starting to become self-sustaining, which is a good analogy for a burning plasma, said Zylstra.
The scientists directed 192 laser beams toward a small target containing a capsule less than a tenth of an inch, or about 2 millimeters 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 that the fuel be incredibly hot in order to burn like a regular fire, but for fusion we need about a hundred million degrees Fahrenheit for decades we have been able to cause fusion reactions in experiments by putting a lot of heat into the fuel, but this isn't good enough to produce net energy from fusion, said Zylstra.
Fusion is starting to dominate over the heating we did for the first time, because of the fusion reactions occurring in the fuel that provided most of the heating. This is a new regime called a burning plasma, according to Zylstra.
Unlike burning fossil fuels or 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 fusing atoms together, just like inside stars, including our sun.
Hundreds of private sector ventures are pursuing a fusion energy future, with some oil companies even investing.
Annie Kritcher of Lawrence Livermore National Laboratory, lead designer for experiments conducted in 2020 and 2021 at the National Ignition Facility, is the holy grail of clean limitless energy, and is the first author of a companion paper published in the journal Nature Physics.
In these experiments, Fusion produced about 10 times as much energy as it went into heating the fuel, but less than 10% of the total amount of laser energy because the process remains inefficient, Zylstra said. Kritcher said that the laser was only used for 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.
It is an enormously complex technological challenge, and it will require serious investment and innovation to make it practical and economical, according to Zylstra. I view fusion as a challenge for it to be a viable source of energy.