The Science of Fusion

New technological advances may enable nuclear fusion to become an energy source

In debates over creating greener and cleaner energy sources, hydroelectric, wind, and nuclear power are commonly discussed as sustainable alternatives to fossil fuels. Nuclear power is the most promising of these sources, as it is more reliable. The nuclear energy source familiar to many people relies on fission reactors, which can produce the energy equivalent of a ton of coal from a small pellet of uranium fuel (1). In the coming decades, technological advancements could enable the development of fusion reactors, a different type of nuclear power that has advantages over fission reactors.

Orange and blue circles represent neutrons and protons, respectively. The small numbers denote the mass number.

Fission vs. Fusion

Fission involves forcefully bombarding a radioactive material (typically uranium) with a neutron, the charge-free particle in an atom. This breaks the attractive force between the protons, electrons, and neutrons of the uranium atom, producing smaller atoms of different elements, such as krypton and barium, that can further decay (2). The fission of one kilogram of uranium creates 24 million kilowatt hours of power (3). Fission is the most efficient form of energy available today (1). Although fission creates radioactive nuclear waste that must be stored for long periods, nuclear reactors do not directly release CO2 and only need to be refueled every 1.5-2 years (1).

Fusion is the process of combining two or more atoms into a larger radioactive atom. Although fusion reactions occur in stars, they have never occurred on Earth (4). However, fusion produces about four times more energy than a similar fission reaction, meaning that fusion could be an excellent energy source if such reactions could be carried out repeatedly (5). A fusion reaction requires a type of matter called plasma, or ionized gas (6). The hydrogen plasma needed for fusion reactions is superheated to millions of degrees. Such extreme temperatures mean that this type of plasma cannot be contained by solids. Scientists have found that powerful magnetic fields could not only contain plasma, but also control the motion of the electrically-charged particles that make up the plasma (7).

Superconducting Magnets

Generating strong magnetic fields to control plasma for fusion reactors requires superconducting magnets. A superconductor is a material that provides no resistance to passing current, meaning that all of the electrical current can be used to generate a magnetic field (8). 

Past designs for fusion reactors, such as the International Thermonuclear Experimental Reactor (ITER) in France, used low-temperature superconductors. Low-temperature superconductors must be cooled to nearly absolute zero (0 Kelvin) using helium, an expensive gas (6). Room- and high-temperature superconducting magnets, which can function at 77 K, would be ideal for fusion reactors because less extensive cooling systems are required for the magnets to still work (6). High-temperature superconductors were first available commercially about eight years ago and remain a developing technology (8).

In 2021, scientists at the Massachusetts Institute of Technology and Commonwealth Fusion System (MIT-CFS) developed a high-temperature superconducting electromagnet 20 times more powerful than any previous one (7). This giant magnet has 20 individual superconducting plates that work together to contain the plasma needed for fusion (7). The chief science officer at Commonwealth Fusion Systems, Brandon Sorbom, told MIT news that “if we [can] build the magnet, all of the physics will work” for a fusion reactor (7). The MIT-CFS team is now working to build a small-scale version of a full-size fusion reactor in order to test their magnet and reactor design. They expect to have a functioning reactor by 2030 (7).

A Fusion Reactor

Designs for nuclear fusion reactors use the tokamak model. A tokamak relies on a magnetic field to hold the plasma in the shape of a torus, or a donut (9). In a fusion reactor, the tokamak is a vacuum chamber that will be filled with hydrogen gas. Then, the gas is heated and ionized to form the hydrogen plasma. A magnetic coil in the center of the tokamak creates a vertical magnetic field, while a magnetic coil around the outside creates a horizontal field (9). The plasma is held by these magnetic fields while fusion occurs. Fusion within the tokamak releases heat, which can be absorbed by the outside of the reactor. Then, just as in a fission reactor, the heat produced is used to vaporize water, which turns a steam turbine, producing electricity (10).

The horizontal (toroidal) magnetic field is created by outer coils, while the vertical (poloidal) magnetic field is created by an inner coil (solenoid). The result forms a helix-shaped magnetic field, which holds the plasma (shown in pink) in a torus shape.

Fusion in the Future

The first functional fusion reactors may be built by 2040, and they could be ready for commercial energy production before 2100 (11). Fusion reactors will have advantages over fission reactors. Fusion reactors are also safer than fission reactors because nuclear accidents cannot occur and no radioactive waste is produced (11). 

Fusion is one of the most promising unharnessed sources of energy, and it may become an integral part of the world’s plan for combating climate change. Fission is one of the main energy sources in the United States and is already used extensively in many European countries. For example, 70% of France’s energy is produced by fission reactors (12). If fusion reactors can be developed cheaply and implemented quickly in many areas, they may provide an easy ‘exit-ramp’ from fossil fuel dependence.


1 Nuclear Provides Carbon-Free Energy 24/7. (2017). Nuclear Energy Institute.

2 Encyclopædia Britannica. (n.d.). Fission product. Britannica Academic. Retrieved January 22, 2022, from

3 Fuel comparison. (2019, May 22). ENS.

4 What is fusion, and why is it so difficult to create? (2018, October 9). NewsCenter.

5 ‌Contrasting Nuclear Fission and Nuclear Fusion. (2020, September 22).

6 Fusion startup plans reactor with small but powerful superconducting magnets. (2021).

7 Chandler, D. (2021, September). MIT-designed project achieves major advance toward fusion energy. MIT News | Massachusetts Institute of Technology.

8 HTS Magnet | SPARC | Research | MIT Plasma Science and Fusion Center. (2018).

‌9 DOE Explains…Tokamaks. (2022).

10 Tokamak. (2015). ITER.

11 Fusion – Frequently asked questions | IAEA. (2016, October 12).

12 Nuclear Power in France | French Nuclear Energy – World Nuclear Association. (2022).