"After repeated verification, such results are not just a flash in the pan." On February 5, scientists published a series of papers in journals such as Physical Review Letters and Nature Physics, confirming that the fusion reactor at the Lawrence Livermore National Laboratory (LLNL) in the United States produced nearly twice the energy input.
In December 2022, LLNL announced that its fusion reactor released more energy than was put in for the first time, becoming a milestone event for fusion reaction. The data in the papers confirmed this: a laser pulse of 2.05 megajoules was fired, generating 3.15 megajoules of energy, equivalent to the energy of three sticks of dynamite. Subsequent experiments saw the energy output-to-input ratio increase again, reaching 1.9 times on September 4, 2023.
However, industry experts seem not optimistic about the commercial prospects of this technology. Some media have mentioned that such a small energy output is far from meeting the requirements for commercial operation, only enough for "taking a hot shower". Currently, all human-operated nuclear power plants rely on fission reactions - the splitting of uranium and other heavy atomic nuclei to release energy and smaller particles. Fusion, on the other hand, is the opposite process, combining lighter atomic nuclei like deuterium and tritium to form heavier helium nuclei while releasing energy.
For decades, scientists have been striving to achieve the 100 million degrees Celsius or higher temperatures needed to produce this reaction. The National Ignition Facility's (NIF) fusion device at LLNL is very small, using laser inertial confinement to compress and heat peppercorn-sized capsules of deuterium and tritium fuel until their core pressure and temperature are sufficient to ignite a fusion reaction. The experiment began in 2011.
However, Richard Town of LLNL points out that NIF was never built to be a prototype for reactor construction nor has it been optimized for increasing production capabilities. The news of reaching the break-even point in 2022 seemed to bring hope for the development of nuclear fusion power plants. However, there is still debate over whether break-even has truly been achieved. In this regard, industry experts are not optimistic.
Martin Freer from the University of Birmingham in the UK said that while achieving fusion is possible with scientific progress, the challenges from a scientific standpoint are quite daunting. Aneeqa Khan from the University of Manchester argued against interpreting these scientific advancements as a feasible solution for humanity to break away from fossil fuel dependence. She emphasized that commercialization of nuclear fusion might take decades and would require intensified global collaboration and investment in talent development.
To develop from a laboratory to a commercial scale, the first problem to solve is how to scale up. The laser used in the experiment came from the OMEGA Laser System at the Laboratory for Laser Energetics at the University of Rochester. Town said that upgrading the lasers could potentially yield a tenfold increase in output ratio.
To ensure symmetry in the experiment, NIF uses eraser-sized gold cylinders to surround the fuel capsules and then heats them with 192 laser beams from all directions. Once a certain temperature is reached, the cylinder emits X-rays to strike the fuel capsules. Due to the smoothing effect of the X-rays, the capsule shell evaporates evenly, and then explodes outwards like a rocket engine, compressing the fuel inward symmetrically.
However, for a gigawatt-scale power plant, this technique is too expensive; it would consume nearly a million gold cylinders and fuel capsules every day. A simpler method is to remove the cylinder and directly shine the laser beams on the fuel capsule, thereby causing it to evaporate. This requires the University of Rochester to provide higher-quality laser beams—that are uniformly distributed in energy across the wavefront, converging in a perfectly symmetrical manner.
On February 5, the Laboratory for Laser Energetics at the University of Rochester reported in a Nature Physics paper that they have adjusted the design of the capsules. By adding silicon to the polymer shell, the energy absorption was improved. The best experimental result was a pulse of 2.15 megajoules generating 1.6 megajoules of energy. Although an energy gain was not achieved, it indeed resulted in plasma burning.
Several startups have reportedly planned to commercialize this technology.
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