(ORDO NEWS) — Scientists from a laboratory in England have broken the record for the amount of energy produced in a controlled, sustained thermonuclear reaction.
The production of 59 megajoules of energy for five seconds at the Joint European Torus (JET) in England was called a “breakthrough” by some news outlets and caused quite a stir among physicists.
But the general line about fusion power generation is that it is “always 20 years away.”
We, a nuclear physicist and a nuclear engineer, are studying how to develop controlled nuclear fusion to generate electricity.
The JET result demonstrates remarkable progress in understanding the physics of fusion. But just as important, it shows that the new materials used to make the inner walls of a fusion reactor work as intended.
The fact that the new wall design works as well as it did sets these results apart from previous milestones and takes magnetic fusion from a dream to a reality.
Nuclear fusion is the fusion of two atomic nuclei into one compound nucleus. This nucleus then decays and releases energy in the form of new atoms and particles, which fly apart from the reaction. A fusion power plant captures the emitted particles and uses their energy to generate electricity.
There are several different ways to safely control fusion on Earth. Our research focuses on the JET approach – using powerful magnetic fields to hold atoms together until they are hot enough to fuse.
Fuel for current and future reactors are two different isotopes of hydrogen – they have one proton, but a different number of neutrons – deuterium and tritium. Ordinary hydrogen has one proton and no neutrons in its nucleus. Deuterium has one proton and one neutron, while tritium has one proton and two neutrons.
In order for the fusion reaction to succeed, the fuel atoms must first be heated enough to strip the electrons from the nuclei. As a result, plasma is formed – a collection of positive ions and electrons.
The plasma must then continue to be heated until it reaches a temperature of over 200 million degrees Fahrenheit (100 million Celsius). This plasma then needs to be kept in an enclosed space at high density for a long enough period of time for the fuel atoms to collide with each other and fuse.
To control fusion on Earth, researchers have developed donut-shaped devices — called tokamaks — that use magnetic fields to trap plasma. The magnetic field lines that wrap around the inside of the donut act like rails along which ions and electrons move.
By feeding energy into the plasma and heating it, it is possible to disperse the fuel particles to such high speeds that when they collide, instead of bouncing off each other, the fuel nuclei fuse together. When this happens, they release energy, mostly in the form of fast moving neutrons.
During fusion, fuel particles are gradually removed from the hot dense core and eventually collide with the inner wall of the fusion vessel.
To prevent the walls from collapsing due to these collisions – which in turn also contaminates the fusion fuel – reactors are built in such a way that they direct the escaped particles into a heavily armored chamber called a divertor. It pumps out distracted particles and removes excess heat to protect the tokamak.
The main limitation of the reactors of yesteryear has been the fact that divertors cannot withstand continuous particle bombardment for more than a few seconds. To make fusion power commercial, engineers need to build a tokamak case that can withstand years of use under the conditions required for fusion.
The wall of the diverter is the first thing to pay attention to. Although the fuel particles are much colder when they reach the divertor, they still have enough energy to knock atoms out of the divertor wall material on impact.
Previously, the wall of the JET diverter was made of graphite, but the graphite absorbs and traps too much propellant for practical use.
Around 2011, JET engineers upgraded the diverter and inner vessel walls with tungsten. Tungsten was chosen in part because it has the highest melting point of any metal – an extremely important property when a divertor is likely to experience thermal loads nearly 10 times the nose cone of a space shuttle entering Earth’s atmosphere.
The inner wall of the tokamak case was replaced by graphite with beryllium. Beryllium has superior thermal and mechanical properties for a fusion reactor – it absorbs less fuel than graphite, yet it can withstand high temperatures.
The power generated by the JET reactor made headlines, but we argue that it is the use of new wall materials that makes the experiment truly impressive, as future devices will need these stronger walls to operate at high power for even longer periods of time.
JET is a successful proof of concept for the next generation of fusion reactors.
The following fusion reactors
The JET tokamak is the largest and most advanced magnetic fusion reactor currently in operation. But the next generation of reactors is already in development, notably the ITER experiment, due to start operating in 2027.
ITER – which means “way” in Latin – is being built in France and financed and managed by an international organization that includes the United States.
ITER will use many of the materials advances that JET has shown to be viable. But there are some key differences as well. First, ITER is huge. The fusion chamber is 37 feet (11.4 meters) high and 63 feet (19.4 meters) in circumference – more than eight times the size of the JET.
In addition, ITER will use superconducting magnets capable of generating stronger magnetic fields for longer periods of time compared to JET magnets. With these improvements, ITER is expected to break JET fusion records, both in energy yield and reaction time.
It is also expected that ITER will be able to do something central to the idea of a fusion power plant: to produce more energy than is required to heat the fuel. Models predict that ITER will generate about 500 megawatts of power continuously for 400 seconds, while consuming only 50 MW of energy to heat the fuel.
This means the reactor produces 10 times more energy than it consumes – a huge improvement over the JET reactor, which needed about three times as much energy to heat the fuel as it produced for its recent record of 59 megajoules.
The recent JET record has shown that years of research in plasma physics and materials science have paid off and brought scientists to the threshold of using fusion for power generation. ITER will provide a huge leap forward towards the goal of industrial-scale fusion power plants. Conversation
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