For decades, humans have tried to harness the power of stars to generate electricity here on Earth. And for almost as long, reaching that goal always seemed just a decade away.
Now, a host of startups are closer than ever, racing to build fusion reactors capable of putting power into the grid.
Merger startups have attracted more than $10 billion in investments, with more than a dozen raising more than 100 million dollars. Many large funding rounds have closed in the past year, with investors drawn to the industry as data center power demand increases and fusion startups near the finish line.
In essence, fusion energy seeks to use the energy released by the fusion of atoms to generate electricity. Humans have known how to fuse atoms for decades, from the hydrogen bomb (an example of uncontrolled nuclear fusion) to any of the countless fusion devices built in laboratories around the world. Experimental fusion devices have been able to control nuclear fusion and one has been able to generate more energy than necessary to cause the reaction.
But none of them have been able to produce enough surplus to make a power plant possible.
To solve that problem, fusion startups are trying several different approaches. Experts have different opinions on which has the best chance of success, although the industry is still on the back foot, so nothing is guaranteed.
Below is a brief overview of the main approaches to fusion energy.
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Magnetic confinement
Magnetic confinement is one of the most widely used techniques, using strong magnetic fields to confine plasma, the soup of superheated particles at the heart of a fusion device.
The magnets must be tremendously powerful. Commonwealth Fusion Systems (CFS), for example, is assembling magnets that can generate magnetic fields of 20 Tesla, which is about 13 times stronger than a typical MRI machine. To handle the amount of electricity needed, the magnets are made of high-temperature superconductors, which must still be cooled to –253˚ C (–423˚ F) using liquid helium.
CFS is currently building a demonstration device called Sparc on a much more accelerated schedule in Massachusetts. The company plans to power it on sometime in late 2026 and, if all goes well, will begin construction on Arc, its commercial-scale power plant, in Virginia in 2027 or 2028.
There are two main types of fusion devices that use magnetic confinement: tokamaks and stellarators.
Tokamaks were first theorized by Soviet scientists in the 1950s and have been widely studied ever since. Tokamaks come in two basic shapes: a donut with a D-shaped profile and a sphere with a small hole in the middle. The Joint European Torus (JET) and ITER are two notable experimental tokamaks; JET operated in the UK between 1983 and 2023, while ITER is expected to begin operations in France in the late 2030s.
UK based Tokamak energy is working on a spherical tokamak design. Its experimental ST40 machine is currently being upgraded.
Stellarators are the other main type of magnetic confinement device. They are similar to tokamaks in that they keep the plasma contained in a donut-like shape. But unlike the geometric sides of the tokamak, the stellarators twist and turn. The irregular shape is determined by modeling the behavior of the plasma and adapting the magnetic field to work with its peculiarities rather than forcing it into a regular shape.
Wendelstein 7-X, a large stellarator with modular superconducting coils operated by the Max Planck Institute for Plasma Physics. has been operating in Germany since 2015. Several startups are also developing their own stellarators, including Upcoming Fusion, Renaissance fusion, thea energyand type one energy.
Inertial confinement
The other main approach to fusion is known as inertial confinement, which compresses the fuel pellets until the atoms within them fuse.
Most inertial confinement designs use pulses of laser light to compress fuel pellets. Several laser beams are fired at once and their light pulses converge on the fuel pellet from all angles at the same time.
So far, inertial confinement is the only approach that has broken a milestone known as the scientific equilibrium point, which is when the reaction releases more energy than it consumed. Those experiments occurred at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California. In particular, measurements to determine the scientific equilibrium point do not include aspects such as the electricity needed to power the experimental facility.
Still, nearly a dozen startups see enough promise in inertial confinement to design reactors around it. focused energy, inertia companies, Marvel Fusionand xcimer are some notable examples that use lasers.
But there are two companies that do not use lasers: First Light Fusion, which proposes using pistons, and Pacific Fusionwhich plans to use electromagnetic pulses instead of lasers.
More to come
Those are the two main approaches to fusion energy, although they are not the only ones. We will soon add more details on alternative designs, including magnetized target fusion, magnetic-electrostatic confinement, and muon-catalyzed fusion.
