As the world continues its journey towards using more sustainable energy sources, nuclear continues to be an important technology. While wind, solar, and hydroelectric power might steal the spotlight in green circles, nuclear power generation technologies are also continuing to develop greener – and more efficient – solutions.
Traditional nuclear power works through the process of nuclear fission, which involves the splitting of a heavy, unstable nucleus into two lighter nuclei. The energy released through this process generates heat to boil water into pressurized steam, which is then used to turn turbines that generate electricity. While this process may sound highly inefficient, it is actually much more efficient than other sources of energy.
However, in addition to the issue of nuclear waste, traditional nuclear power has a lot of room for improvement. Specifically, the process of fission leaves a lot of atomic energy on the table. If nuclear energy were to generate power through nuclear fusion instead, a lot more energy could be produced.
While fission works by splitting atoms apart, fusion is the process where two light nuclei combine together. This releases vast amounts of energy — this is the process that powers the sun. Fusion not only creates less radioactive material than fission, but it requires much less material to begin with, and offers a nearly unlimited fuel supply.
So why don't we use nuclear fusion to power our world today? Well, because scientists have had a really hard time sustaining and controlling nuclear fusion reactions.
One of the foremost technologies for nuclear fusion is the Tokamak reactor, which is a donut-shaped magnetic containment device that is designed to harness fusion power.
While the tokamak design was originally developed in the 1960s, it's taken more than 50 years for the technology to develop enough to be considered for practical use. Russian physicist Oleg Lavrentiev first devised the design, and it was later developed by Igor Tamm and Andrei Sakharov. Today, it is one of several types of magnetic confinement devices being developed to produce controlled thermonuclear fusion power. It is currently the leading candidate for a practical fusion reactor.
But what makes the Tokamak design so special that it's able to theoretically, harness the power of fusion?
How tokamak reactors work
The heart of a tokamak is its doughnut-shaped vacuum chamber.
Inside the chamber, gaseous hydrogen fuel is placed under extreme heat and pressure, turning into a plasma—a hot, electrically charged gas.
The charged particles of the plasma can be controlled by massive magnetic coils placed around the chamber. ("tokamak" is a Russian acronym that stands for "toroidal chamber with magnetic coils".) The control is necessary in order to keep the plasma away from the walls of the chamber — contact between the electrically-charged plasma and the reactor walls could cause a near-instantaneous meltdown.
A powerful electrical current is run through the vessel, and the gaseous hydrogen fuel becomes ionized (electrons are stripped from the nuclei) and forms a plasma.
As the plasma particles become energized and collide they also begin to heat up. Additional heating methods help to bring the plasma to fusion temperatures (between 150 and 300 million °C). The particles become "energized" enough to overcome their natural electromagnetic repulsion on collision to fuse, releasing huge amounts of energy.
All of this may sound simple enough, so why isn't it more common? Largely because sustaining plasma with such high energy levels for any sizeable period of time is rather hard.
The biggest problem with the tokamak design is that of the heating of the plasma inside. In order for the plasma to get hot enough for fusion reactions to occur, it has to reach temperatures upwards of 100 million degrees celsius. In simpler terms, it has to reach temperatures four times that of the sun.
This is traditionally done through magnetic compression or high-frequency microwaves, but the energy needed to kickstart and sustain the initial reaction is high. In theory, once a Tokamak reactor is kickstarted, it could fully sustain itself and continue creating massive amounts of energy. But that hasn't happened yet – we still don't have a net positive tokamak fusion reactor. But we're getting close.
After the tokamak reactor creates enough energy to create the plasma, the plasma itself generates a significant number of neutrons, which start spinning around the inside of the reactor. The neutrons eventually spin out to the reactor wall, heating it up. This heat from the neutrons can be used to generate energy, however, scientists also have to keep the tokamak reactors from overheating and melting down.
The process of cooling tokamak reactors is also a fairly energy-intensive one, requiring a cryogenic cooling system utilizing helium and liquid hydrogen. While this entire process has been shown to work, it still isn't enough to sustain tokamak operation for more than 70 seconds, at least right now, which is a record held by the Korean Superconducting Tokamak Advanced Research reactor (KSTAR), set in 2016.
The future of nuclear fusion
At the present, the largest tokamak reactor in the world is the ITER, or the International Thermonuclear Experimental Reactor, which is being constructed in France, with most of it scheduled for completion in 2021. The machine is scheduled to be turned on in 2025 and is a joint program between the EU, India, China, Russia, Japan, the United States, and South Korea.
When completed and brought online, it will theoretically produce 500 MW of energy, which should be enough to start the fusion reaction inside and cool itself down. At present, researchers don't have any plans to use the excess heat from the reactor to generate electricity, but a successful test run of the ITER would lay the groundwork for sustainable nuclear fusion globally.
When fully completed, the ITER tokamak will contain as much metal as 3 Eiffel Towers, be capable of creating plasma at 150 million degrees Celsius, or 5 times greater than the core of the sun, and produce a tenfold increase in the energy input into the system. In other words, ITER designers theorize that inputting 50 MW of energy into the system to kickstart the reactor will result in 500 MW produced. Notably, the internal volume of the ITER tokamak is record-setting. According to ITER itself,
"The ITER Tokamak will be the largest ever built, with a plasma volume of 830 cubic meters. The maximum plasma volume in tokamaks operating today is 100 cubic meters—reached in both Europe's JET and Japan's JT-60. ITER's huge plasma volume will enable it to produce, for the first time, a "burning plasma" in which the majority of the heating needed to sustain the fusion reaction is produced by the alpha particles generated during the fusion process itself. The production and control of such a self-heated plasma has been the goal of magnetic fusion research for more than 50 years."
Aside from the ITER project, much research is currently underway investigating the future of nuclear fusion.
When, or if, nuclear fusion is proven out as a sustainable energy generation method, it will be fully waste-free and capable of powering entire cities through just one reactor. After all, it's the power of choice of Iron Man.