Nuclear fusion comes two steps closer | The World Weekly
As the world faces up to the threat posed by climate change, the implications of nuclear fusion research could be hugely important in the pursuit of alternative energy sources. If we can construct a nuclear fusion reactor which is capable of producing and containing hydrogen plasma - a superheated cloud of hydrogen particles - for a long enough period, the tantalising possibility of clean and near-limitless energy will be achievable.
It is promising then that over the last week, two experimental results emerged which were hailed as significant milestones for nuclear fusion technology. On Wednesday, German Chancellor Angela Merkel pressed a button to initiate a test at the experimental Wendelstein 7-X fusion reactor in Germany, that successfully managed to produce and contain hydrogen plasma for a quarter of a second.
Then, just five days later, with the scientific community still digesting the news from Germany, Chinese scientists at a rival reactor, the Experimental Advanced Superconducting Tokamak (EAST), made a surprise announcement. They revealed that they had managed to produce and contain hydrogen plasma for a record 102 seconds, far longer than the Wendelstein, albeit at a much lower temperature – around 50 million degrees Celsius, as opposed to 80 million degrees Celsius.
The temperature of the plasma inside the ESTA is roughly three times hotter than the core of the sun. However, this pales in comparison to the hottest ever man-made temperature. Temperatures inside the Large Hadron Collider in Switzerland reached 5.5 trillion degrees Celsius for a fraction of a second, during an experiment designed to create exotic forms of matter which only existed in the first few moments after the Big Bang. This was, as far as we know, the hottest temperature in the universe at that point. Meanwhile, the hottest man-made plasma ever created reached 510 degrees Celsius at the Tokamak Fusion Test Reactor, in Princeton, New Jersey, which operated between 1982 and 1997.
How fusion works
So how does nuclear fusion work and what are the implications of the experimental results coming from China and Germany?
Fusion reactors work by heating particles to millions of degrees Celsius while suspending and containing the resulting plasma using incredibly powerful, super-cooled magnets. In this superheated state, the particles in the atoms collide with each other and fuse together, resulting in the creation of huge amounts of energy. This is the same process of energy production which occurs in the core of stars. The ultimate goal of fusion reactors is to harness the energy that is produced in this process.
They have been around in various forms since the 1950s. However, true fusion is extraordinarily difficult to achieve because any viable reactor must produce more energy than it consumes. For this to happen, hydrogen plasma must be heated and contained at a sufficient density and heat, and for long enough periods of time, to initiate a reliable chain reaction of fusion events, without damaging the walls of the reactor
The concept of producing more energy than is consumed has been demonstrated, albeit on a very small scale, in an experiment carried out at The National Ignition Facility (NIF) in the United States, where scientists produced as much as 2.6 times more energy than was present in the fuel.
Once the technology is sufficiently advanced, scientists hope nuclear fusion could have the potential to provide a near limitless source of clean energy using virtually inexhaustible raw materials. This is because any viable reactors will eventually run on deuterium, a stable isotope of hydrogen which can be easily extracted from seawater.
In fact, Associate Professor at Sydney University Joe Khachan has told the Sydney Morning Herald that "there is enough deuterium in the world's oceans and water to supply humanity's energy needs for the next 5 billion years”. This is why the hydrogen plasma breakthroughs are such promising developments.
It is also generally agreed by scientists that nuclear fusion is much safer than nuclear fission – the process utilised in current nuclear power plant designs – because there is no chance of meltdown and the technique does not produce any radioactive waste. In addition, the only major byproduct of the process is helium, an inert gas.
Nuclear fission works by splitting atoms to produce energy rather than fusing them together.
The two major types of fusion reactors are called stellarators, like the Wendelstein, and tokamaks like the EAST. They are designed using the same basic concepts, however there are some differences in the way they work. Tokamaks, the more traditional design of the two, utilise a huge network of magnets in a doughnut-shaped ring. They create plasma in pulses, which means that they have to be turned on and off and refuelled to produce new plasma.
A stellarator on the other hand is designed like a twisted tokamak, with each ring that comprises the structure of the tokamak, contorted in a very precise way according to complex mathematical calculations. The practical advantage of this is that while tokamaks can only work in short bursts, a stellarator could, in theory, run continuously.
The potential of stellarators has been recognised for many years but they are incredibly difficult to construct in comparison to other types of reactors, meaning few have ever been completed. Only state-of-the-art computer design technology has made construction of the Wendelstein possible.
Both the Chinese and German reactors are proof-of-concepts, so they are not designed to harness any energy they produce, but their respective breakthroughs are exciting in their own ways, even though the length of time they can produce plasma appears short.
The Wendelstein’s feat was the first time that a stellarator design was able to successfully produce and contain hydrogen plasma. Scientists predict that in future experiments, the reactor will be capable of maintaining plasma at the necessary heat for fusion, for up to 30 minutes.
Hydrogen plasma had been produced and contained in other types of reactors before the Wendelstein's experiment. The facility has also been producing helium plasma in experiments since December, in what is considered an easier and less useful process.
Results from the Chinese reactor, on the other hand, are promising because they demonstrate that tokamak reactors can produce and contain hydrogen plasma for a significant amount of time, even though they are limited to working in bursts.
It should be made clear that the results from China have not yet been peer-reviewed, but the team has already set a target of heating the hydrogen plasma to 100 million degrees – considered the ideal temperature for fusion - for 1,000 seconds in future experiments.
The encouraging signs from both stellarator and tokamak technologies could pave the way for new, more effective kinds of reactors in the future. Thomas Klinger, director at the Max Planck Institute where the Wendelstein reactor is based, told phys.org that the two differing designs do not necesarily need to compete against each other.
“It's not a race,” he said. “In the end they do not represent two different worlds; the two branches of research provide mutual inspiration for each other. Insights from stellarator research have been incorporated into the development of the tokamak and vice versa. They are two pillars of a large edifice. The exact form the edifice will ultimately take is something we do not yet know. It is even conceivable today that a fusion power plant will be built one day as a hybrid of the two types.”
Promisingly, another experimental tokamak reactor, is currently under construction in France, led by an international team of scientists and engineers from the EU, India, Japan, China, Russia, South Korea and the United States. The International Thermonuclear Experimental Reactor (ITER) is set to be the largest in the world and promises to make the transition from experimental studies, to demonstrating the principle of producing more energy than is used, by heating hydrogen plasma on a large scale, at super-high temperatures, and for extended periods of time.
It aims to produce 500 megawatts of power in 400 second bursts while only requiring only 50 megawatts to operate. In other words, it will produce ten times the power that it requires to run on. ITER was slated to begin operations in 2020, however, the project has been delayed due to a series of technical problems and rising costs.
If this is achieved and advances are made in other areas, the next generation of fusion reactors have the potential to revolutionise the world’s energy supply, however, a working, commercially viable version is still likely to be decades away from completion.