Scientists from a laboratory in England have broken the record for the amount of energy produced during a controlled, long-term synthesis reaction.
The production of 59 megajoules of energy in five seconds during the Joint European Torus experiment – or JET – in England, some news agencies called a “breakthrough” and caused quite a stir among physicists.
But the common line regarding the production of electricity with a nuclear nucleus is that it is “always 20 years”.
We are a nuclear physicist and a nuclear engineer who are studying how to design controlled nuclear fusion in order to generate electricity.
The JET result demonstrates remarkable advances in understanding the physics of synthesis. But no less important is the fact that it shows that the new materials used to build the inner walls of the fusion reactor worked as intended.
The fact that the new wall design performed just as well separates these results from the previous stages and raises the magnetic synthesis from dream to reality.
Fusion of particles together
Nuclear fusion is the fusion of two atomic nuclei into one complex nucleus. This nucleus then disintegrates and releases energy in the form of new atoms and particles that are accelerated by the reaction. A fusion power plant will capture the particles that explode and use their energy to generate electricity.
There are several different ways to safely control thermonuclear fusion on Earth. Our research focuses on the JET approach – using powerful magnetic fields to hold atoms until they heat up to a temperature high enough for them to merge.
Fuels for current and future reactors are two different isotopes of hydrogen – meaning they have one proton but different numbers of neutrons – deuterium and tritium. Normal hydrogen has one proton and no neutrons in its nucleus. Deuterium has one proton and one neutron, and the third has one proton and two neutrons.
For the fusion reaction to be successful, the fuel atoms must first heat up so that the electrons break out of the nuclei. This creates a plasma – a collection of positive ions and electrons.
You then need to continue heating this plasma until it reaches a temperature of more than 200 million degrees Fahrenheit (100 million degrees Celsius). This plasma must then be kept in an enclosed space with a high density for a sufficiently long period of time for the fuel atoms to collide with each other and merge.
To control the thermonuclear process on Earth, researchers have developed donut-shaped devices – so-called tokamaks – that use magnetic fields to hold plasma. The magnetic field lines that wrap around the donut act like trains on which ions and electrons travel.
By introducing energy into the plasma and heating it, you can accelerate the fuel particles to such a high speed that when they collide, the fuel nuclei merge rather than repel each other. When this happens, they emit energy, primarily in the form of fast-moving neutrons.
During the synthesis process, the fuel particles are gradually removed from the hot dense core and eventually collide with the inner wall of the fusion vessel.
To prevent wall degradation due to these collisions – which in turn also contaminate thermonuclear fuel – the reactors are built so that they direct headstrong particles into a heavily armored chamber called a diverter. This pumps out distracted particles and removes excess heat to protect the tokamak.
Walls are important
The main limitation of past reactors was the fact that diverters could not survive constant bombardment with particles for more than a few seconds. In order for fusion electricity to work commercially, engineers need to build a tokamak ship that will last years of use in the conditions necessary for fusion.
The defensive wall is the first attention. Although fuel particles are much colder when they reach the diversion, they still have enough energy to knock atoms out of the diverter wall material when it collides with it.
Previously, the JET diverter had a wall of graphite, but graphite absorbs and retains too much fuel for practical use.
Around 2011, JET engineers upgraded the diverter and inner vessel walls to tungsten. Tungsten was chosen in part because it has the highest melting point of any metal – an extremely important feature when the distractor is likely to experience heat loads almost 10 times higher than the nasal cone of a space shuttle returning to Earth’s atmosphere.
The inner wall of the takamaka was reworked from graphite to beryllium. Beryllium has excellent thermal and mechanical properties for a fusion reactor – it absorbs less fuel than graphite, but can still withstand high temperatures.
The energy JET produced in the headers has led to headlines, but we can argue that in fact this use of new wall materials makes the experiment really impressive because future devices will need these more robust walls to run at high power for even longer periods. time.
JET is a successful proof of the concept of how to build the next generation of fusion reactors.
The following fusion reactors
The Tokamak JET is the largest and most advanced magnetic thermonuclear reactor currently operating. But the next generation of reactors is already running, primarily the ITER experiment, which is due to begin operations in 2027.
ITER – which means “path” in Latin – is being built in France and is funded and run by an international organization that includes the United States.
ITER is going to use many tangible achievements that JET has shown to be viable. But there are some key differences. First, ITER is massive. The fusion chamber is 37 feet (11.4 meters) high and 63 feet (19.4 meters) around – more than eight times larger than the JET.
In addition, ITER will use superconducting magnets capable of creating stronger magnetic fields over longer periods of time compared to JET magnets. It is expected that with the help of these upgrades ITER will break records for thermonuclear nuclear nuclei – both in terms of energy output and reaction time.
ITER is also expected to do something central to the idea of a fusion power plant: produce more energy than is needed to heat fuel. Models predict that ITER will generate about 500 megawatts of energy continuously for 400 seconds, consuming only 50 MW of energy to heat fuel.
This means that the reactor produces 10 times more energy than it consumes – a huge improvement over the JET, which needed about three times more energy to heat fuel than it produced for its recent record of 59 megajoules.
Recent JET records have shown that years of research in plasma physics and materials science have paid off and have led scientists to the threshold of using synthesis to generate electricity. ITER will make a huge leap forward towards the goal of industrial fusion power plants.
David Donavan, Associate Professor of Nuclear Engineering, University of Tennessee and Libya Casali, Associate Professor of Nuclear Engineering, University of Tennessee.
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