N-fusion: The clean energy the world needs, but may not get soon enough
For the first time, a nuclear fusion experiment has achieved ignition, generating more energy that it consumed. While there are miles to go before fusion can become the source of the world’s energy needs, the results mark a milestone in scientific terms
In the quest for perfecting the science of nuclear fusion in practice (the theory is well understood), the energy produced has never matched the energy that has gone into the effort. Until now, with the US energy department having announced that fusion ignition has been achieved at the California-based Lawrence Livermore National Library (LLNL).
Fusion ignition means that the fusion procedure produced more energy than it consumed. From an input of 2.05 megajoules, the fusion reaction at LLNL resulted in the release of 3.15 megajoules, an increase of around 54%
What does that mean for the future of using fusion to generate energy for the world’s needs? The energy department said in a statement that the breakthrough will pave the way for advancements in [US] national defence and the future of clean power. While it is indeed a scientific breakthrough, the question that begs an answer is how far we still are from using fusion-induced energy as the solution to the world’s energy problems.
Reports about fusion breakthroughs have not always lived up to the hype. The best-known instance is that of claims by two chemists in 1989 about having achieved “cold fusion”, or fusion achieved at room temperature. The experiments at LLNL involve “hot fusion”, with reactions at extremely high temperatures.
More recently, in 2013, BBC reported that LLNL had achieved a “nuclear fusion milestone”. A subsequent report in Science explained why it was not really a breakthrough. While the energy yield did exceed the energy absorbed in a key step of the process, it was still a fraction of the total energy used in the overall experiment.
How fusion works
Nuclear fusion involves forming a heavier substance from the atoms of two lighter ones, whose nuclei are merged. In the process, some of the initial mass is transformed into energy.
In the 1920s, British astronomer Arthur Eddington hypothesised that this is what happens within the Sun, resulting in the release of an immense amount of energy. In the 1930s, German-American scientist Hans Bethe determined that in the Sun, the reaction involves fusing four hydrogen atoms into a helium atom — work that earned him the Nobel Prize for Physics in 1967.
In contrast, nuclear fission, the process that drives all nuclear energy plants, involves breaking the bonds between subatomic particles, leading to the release of energy. Nuclear fission needs an immense amount of control to prevent unwanted reactions that could lead to an explosion. The substances it requires, such as uranium, are not as widely available as hydrogen for fusion.
Fusion, however, is difficult to achieve. While science has advanced enough to produce temperatures in millions of degrees, maintaining that temperature is difficult, because no container can hold anything that hot. One solution is to use a magnetic field to contain the plasma (the state of matter when the atoms have been stripped of their electrons), an area where research is still going on.
The other challenge is producing enough energy so that the energy spent is worth the effort.
What happens at LLNL
While hydrogen is abundantly available, it is not easy to bring it to fusion. Fusion experiments have, therefore, focused on fusing hydrogen isotopes, or different forms of the same element: their atoms have the same number of protons but a different number of neutrons.
Hydrogen’s nucleus contains a proton and no neutrons. The LLNL reactor uses two isotopes of hydrogen, deuterium (one neutron) and tritium (two neutrons), whose fusion leads to the formation of helium atoms and the release of energy.
LLNL directs 192 laser beams on a hohlraum, a gold cylinder inside which a tiny capsule contains atoms of deuterium and tritium. This approach is called "inertial-confinement fusion".
Energy in and out
The results of the latest LLNL experiment — 3.15 megajoules of energy released against an input of 2.1 megajoules — mark an achievement that is huge in scientific terms, and laboratory-scale as far as the numbers are concerned.
“In its present form, it cannot become a source of energy. However, scientifically & technologically, it represents an important milestone,” Dr Shashank Chaturvedi, director of the Institute for Plasma Research in Gandhinagar, said in an email response.
“It means that one now understands how to create capsules that are stable when they undergo implosion at extreme velocities and densities. By themselves, the results will yield new insights for ultra-dense matter and strategic objectives for which NIF has developed lasers,” he said.
NIF is the US National Ignition Facility housed at LLNL. It has made progress with successive experiments over the years. In August 2021, it achieved an energy output of 1.35 megajoules. LLNL’s press release last year did not mention how much energy it used for this; New Energy Times put it at 1.9 MJ.
The newest announcement means that fusion with net energy gain is achievable. Where that will lead to is a question that may take a long time to answer.
The cold fusion controversy
In 1989, Martin Fleischmann and Stanley Pons two chemists at the University of Utah, Salt Lake City, claimed at a press conference that they had achieved nuclear fusion at room temperature. The phrase “cold fusion” derives from their claim.
The two scientists described a device they had made, in which electrolysis broke down heavy water (water in which the hydrogen atoms are replaced with deuterium). The deuterium released collected on a palladium pole, where their nuclei fused and released energy, they claimed.
The claim was met with scepticism by the scientific community. Several other teams tried the experiment Fleischmann and Pons had described, but they did not achieve the same result.
While it is often cited as an example of failed science, commentators today note that fraud was never established, either on the part of Fleischmann and Pons, or that of those who dismissed their claims.