A milestone has been reached in the 60-year struggle to harness the nuclear reactions that power the Sun in an experiment that could lead to a way of producing an unlimited source of clean and sustainable energy in the form of nuclear fusion.
Scientists in California said on Wednesday that they have for the first time managed to release more energy from their nuclear fusion experiment than they put into it, which marks a critical threshold in eventually achieving the goal of a self-sustaining nuclear-fusion reaction.
Nuclear fusion uses a fuel source derived from water and produces none of the more dangerous and long-lasting isotopes, such as enriched uranium and plutonium, that result from conventional nuclear power plants, which rely on the fission or splitting of atoms rather than their fusion.
Researchers involved in the Nuclear Ignition Facility (NIF) at the Lawrence Livermore National Laboratory said that they have used 192 laser beams to compress a tiny fuel pellet less than half the diameter of a human hair in such a way that it triggered the net release of energy by nuclear fusion. The fuel, composed of the two hydrogen isotopes tritium and deuterium derived from water, was compressed together under enormous pressures and temperatures for less than a billionth of a second, but this was enough to see more energy coming out of the experiment than went into it.
"We are fusing deuterium and tritium, which are isotopes of water, in a way that gets them to run together at high enough speed to overcome their natural electrical repulsion to each other," said Omar Hurricane of the Livermore laboratory. "We are finally, by harnessing these reactions , getting more energy out of these reactions than we are putting into the deuterium-tritium fuel... We took a step back from what we tried before and in the process took a leap forward," said Dr Hurricane, who led the NIF study published in the journal Nature.
There are currently two parallel approaches to nuclear fusion. One uses laser energy to compress fuel pellets - like the NIF experiment - and aims to keep the fuel in place by a process known as inertial confinement.
The other approach is to build a complex magnetic "bottle" to hold the hot, electrically charged plasma of the fuel in place. This magnetic confinement is the strategy of the Joint European Torus experiment in Culham, Oxfordshire, and the international ITER nuclear fusion plant under construction at Cadarache in southern France.
Both approaches aim to gain more energy than is put into the system, and ultimately to a critical stage called "ignition" when the reaction becomes self-sustaining, which would mean that fusion could be exploited practically in power plants as an unlimited source of clean energy. The breakthrough at NIF was made possible by altering the laser pulses focusing on the fuel pellet in such a way that it led to the even compression of the capsule holding the deuterium and tritium, said Debbie Callahan, one of the researchers involved. -TOI
US scientists achieve 'turning point' in fusion energy quest WASHINGTON: US scientists announced on Wednesday an important milestone in the costly, decades-old quest to develop fusion energy, which, if harnessed successfully, promises a nearly inexhaustible energy source for future generations. For the first time, experiments have produced more energy from fusion reactions than the amount of energy put into the fusion fuel, scientists at the federally funded Lawrence Livermore National Laboratory in California said. The researchers, led by physicist Omar Hurricane, described the achievement as important but said much more work is needed before fusion can become a viable energy source. They noted that did not produce self-heating nuclear fusion, known as ignition, that would be needed for any fusion power plant. Researchers have faced daunting scientific and engineering challenges in trying to develop nuclear fusion - the process that powers stars including our sun - for use by humankind. "Really for the first time anywhere, we've gotten more energy out of this fuel than was put into the fuel. And that's quite unique. And that's kind of a major turning point, in a lot of our minds," Hurricane told reporters. "I think a lot of people are jazzed." Unlike fossil fuels or the fission process in nuclear power plants, fusion offers the prospect of abundant energy without pollution, radioactive waste or greenhouse gases. Unlike the current nuclear fission energy that is derived from splitting atoms, fusion energy is produced by fusing atoms together. Experts believe it still will be many years or decades before fusion can become a practical energy source. "I wish I could put a date on it," said Hurricane. "But it really is (just) research. And, you know, although we're doing pretty good, we'd be lying to you if we told you a date." Of the uncertain path ahead in fusion research, Hurricane compared it to "climbing half way up a mountain, but the top of the mountain is hidden in clouds. You can't see it. You don't have a map". The research was conducted at the laboratory's National Ignition Facility (NIF), which was completed in 2009. Zap a tiny target The scientists used 192 laser beams to zap a tiny 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, which are two isotopes, or forms, of hydrogen. The fuel was coated on the inside of the capsule in a frozen layer less than the width of a human hair. At very high temperatures, the nucleus of the deuterium and the nucleus of the tritium fuse, a neutron and something known as an "alpha particle" emerge, and energy is released. The experiments, published in the journal Nature, created conditions up to three times the density of the sun. In two experiments described by the researchers that took place in September and November of last year, more energy came out of the fusion fuel than was deposited into it, but it was still less than the total amount deposited into the target. The deuterium-tritium implosions were more stable than previously achieved. The researchers did so by doubling the laser power earlier in the laser pulse than in earlier tries. The fusion-energy yield was increased by about tenfold from past experiments, in a series that started last May. One of the experiments produced more than half of the so-called Lawson criteria needed to reach ignition - but only about one-100th of the energy needed for ignition. Lawrence Livermore National Laboratory, located about 45 miles (70 km) east of San Francisco, is overseen by the National Nuclear Security Administration, an agency of the US Department of Energy. Eager to exploit the potential this type of energy offers to reduce dependence on oil and other fossil fuels, the United States and other nations have invested many millions of dollars into fusion research, often with uneven results. There are two main approaches. This team focuses on what's known as inertial confinement fusion energy - using lasers to compress fuel pellets, which triggers fusion reactions. Other labs like the Culham Centre for Fusion Energy, which is the British national laboratory for fusion research, and the Princeton Plasma Physics Laboratory in New Jersey focus on magnetic confinement fusion energy - putting plasma in a magnetic container and heating it up until nuclei fuse. Steve Cowley, director of the Culham Centre, called new findings "truly excellent" but said different measures of success make it hard to compare with his type of research. "We have waited 60 years to get close to controlled fusion, and we are now close in both magnetic and inertial confinement research. We must keep at it," Cowley said in a statement. Mark Herrmann, a fusion researcher at Sandia National Laboratories in New Mexico which is also overseen by the US National Nuclear Security Administration, called the new findings important, but sees a "very long road to assessing the viability of fusion as a long-term energy source". "I believe a compact carbon-free energy source is very important for humankind in the long term," he said by email. "Fusion is one bet. If it pays off, the return will be big."
-TOI
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