How does fusion power work and the principles behind it

For decades people have wanted to use the energy of the stars to generate electricity here on Earth. And for a long time, achieving that goal seemed only ten years away.

Now, many startups are closer than ever and rushing to build fusion reactors that can put power on the grid.

Fusion startups have attracted more than $10 billion in investments, more than a dozen of which have raised more than $100 million. Several large funding rounds have closed over the past year, with investors drawn to the industry as demand for power from data centers grows and as fusion startups near the finish line.

At its core, fusion energy seeks to harness the energy released from the fusion of atoms to produce electricity. Humans have been fusing atoms together for decades, from the hydrogen bomb – an example of uncontrolled nuclear fusion – to any number of fusion machines built in labs around the world. Experimental fusion machines were able to control nuclear fusion, and man was able to produce more energy than was needed to trigger a reaction.

But none of them have been able to produce enough surplus to make a power plant feasible.

To solve that problem, fusion developers are trying many different methods. Experts have different opinions about the best chances of success, although the industry is still young, so nothing is guaranteed.

Here is a brief summary of the main methods of fusion power.

Magnetic confinement

Magnetic confinement is one of the most widely used methods, using strong magnetic fields to confine the plasma, the soup of superheated particles at the heart of the fusion device.

The magnets must be very strong. Commonwealth Fusion Systems (CFS), for example, includes magnets that can produce 20 tesla magnets, 13 times stronger than a conventional MRI machine. To handle the required amount of electricity, the magnets are made of high quality superconductors, which still need to be cooled to -253˚ C (–423˚ F) using liquid helium.

CFS is currently building a demonstration device called Sparc on a highly accelerated timeline in Massachusetts. The company expects to open it sometime in late 2026, and if all goes well, it will begin construction at 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 described by Soviet scientists in the 1950s, and since then, they have been widely studied. Tokamaks come in two basic shapes – a donut with a D-shaped profile and a circle with a small hole in the middle. The Joint European Torus (JET) and ITER are two notable experimental tokamaks; JET was operational in the UK between 1983 and 2023, while ITER is expected to start operating in France in the late 2030s.

UK-based Tokamak Energy is working on a circular tekamak design. Its ST40 test rig is currently under development.

Stellarators are another main type of magnetic confinement device. They are similar to tokamaks in that they store plasma contained within a donut-like shape. But unlike Tokamak’s geometric sides, stellarators twist and turn. The irregular shape is determined by modeling the behavior of the plasma and manipulating the magnetic field to work with its constraints instead of forcing it into a regular shape.

Wendelstein 7-X, a giant star 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 Proxima Fusion, Renaissance Fusion, Thea Energy, and Type One Energy.

Internal confinement

The other main fusion method is known as inertial confinement, which compresses the fuel pellets down to the atoms inside the fuse.

Most passive confinement designs use pulses of laser light to compress fuel pellets. Several laser beams are fired at the same time, and their light pulses converge on the pellet fuel from all angles simultaneously.

So far, inertial confinement is the only method that has broken the milestone known as scientific breakeven, which is when a reaction releases more energy than is consumed. That test took place at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California. Notably, the measurements to determine scientific diversity do not include things like the electricity needed to power the experiment.

Still, about a dozen startups see enough promise in internal confinement that they are designing reactors around it. Focused Power, Inertia Enterprises, Marvel Fusion, and Xcimer are some notable examples using lasers.

There are two companies that don’t use lasers, though: First Light Fusion, which proposes to use pistons, and Pacific Fusion, which plans to use electromagnetic pulses instead of lasers.

More to come

Those are the two main forms of fusion power, though not the only ones. Soon, we will add more details about different designs including magnetized fusion target, magnetic-electrostatic confinement, and muon-catalyzed fusion.