by Brianna Alico
figures by Aparna Nathan
The phrase “energy crisis” likely brings to mind rising gas prices, drying up oil reserves, increasing greenhouse gases, climate change, and the like. Scientists, politicians, and civilians alike are working to combat this crisis by creating plans and developing clean energy sources such as solar panels and wind turbines, which generate energy with relatively little carbon emission. Currently, wind turbines, solar panels, and hydroelectric power plants generate around 20% of the electricity used in the United States. However, scientists believe that we can do even better through fusion energy, which uses small amounts of highly abundant natural resources to generate energy in the same way that stars–like our Sun–do. While the physical process of fusion is essentially the reverse of nuclear fission, fusion is believed to be a safer and more efficient (albeit more difficult) alternative to fission. Physicists around the world are now racing to develop this breakthrough energy technology using an unlikely source: magnets.
What is fusion energy?
Fusion occurs when two or more atoms, the particles that make up all things, combine to make a single, new type of atom (Figure 1). But this doesn’t happen spontaneously: because atoms are made of positively and negatively charged particles known as protons and electrons, they will often repel each other if they get too close. This is similar to how the “negative” poles of two bar magnets will repel each other if you try to push them together. Fusion can only occur under special conditions where atoms are moving so fast that their kinetic energy–the energy the atom possesses due to its motion–overcomes the repulsive forces, increasing the probability that the centers of the atoms, known as nuclei, will collide and fuse into one. An atom’s speed can be increased by raising the temperature of the system that the atom is in. When the temperature is raised, energy in the form of heat is absorbed by the atoms and converted to kinetic energy, allowing them to move faster.
When the particles do achieve fusion, energy is released (Figure 1). This energy can then be harnessed for other processes, such as powering an electrical generator. Current fusion devices use the byproducts of the reaction to create even more fuel, essentially creating a self-sustaining process. Achieving energy-efficient fusion, however, is a decades-old hurdle. Because fusion energy requires huge amounts of heat, it has been a challenge to develop fusion devices that generate more energy than they use, a standard that physicists refer to as Q>1. For this reason, scientists are continually working to find new sources and technologies to achieve fusion energy. Some scientists have turned to plasma to accomplish this goal.
What is plasma?
Plasma is a special state of matter in which charged atoms known as ions exist in a gaseous form. Neon lights, our Sun, and lightning are all examples of plasma. As in all gases, the atoms in plasma are highly mobile and move with high speeds. The movement of its many charged particles make plasma capable of conducting electricity and being affected by magnetic fields. This property is key for the new fusion methods that physicists and engineers are developing. Scientists create plasma by superheating gaseous hydrogen, which is the most abundant element in the universe.
How are magnets involved in fusion?
All magnets generate a magnetic field that can direct the movement of charged particles within said field (Figure 2). A magnet’s field strength is measured in Teslas (T); refrigerator magnets have a field strength of around 0.001T, while that of a magnetic resonance imaging (MRI) machine is around 1.5T. Unlike radiation, low-strength magnetic field exposure has no known long-term adverse health effects. In fact, we are constantly exposed to the Earth’s own magnetic field (0.00003T)!
The most powerful magnets being developed today are made of a special technology known as high-temperature superconductors (HTS). These superconductors can carry an immense amount of electrical current with low dissipation, meaning very little of the current is lost to the environment. We can think of HTS like energy efficient light bulbs: such bulbs will convert a high percentage of their electricity into light and will lose very little energy in the form of heat. Remembering that physicists must attain Q>1 by generating more energy than is put in for fusion energy to be efficient, it’s of the utmost importance to use technologies and parts that are as efficient as HTS. The high current carried by HTS in turn creates a very strong magnetic field–as strong as 20T or more. The generated magnetic fields are so powerful that they can confine plasma inside the field, directing the atoms to stay within a particular space. This confinement, which is referred to as a plasma bottle, increases the chances of two ions meeting and fusing while also safely containing the super-heated plasma inside of the magnet and away from the walls of the device (Figure 3). Keeping the plasma away from the device is essential, as its extreme temperatures (over 100 million degrees Fahrenheit) would melt the metal walls.
How safe and efficient is plasma-based fusion?
Fusion is essentially the opposite of fission, which is the process of splitting one heavy atom into two or more lighter atoms. Unlike in nuclear fission, the byproducts of fusion are not radioactive. A major byproduct of hydrogen fusion devices is helium gas, which can be used to cool certain medical devices (and fill balloons!). The reactions can also quickly be stopped by decreasing the temperature of the plasma, so that the ions within it slow down and are no longer capable of fusing. In the event that containment of plasma is lost, fusion reactions cease immediately; this is much safer than meltdowns of nuclear fission reactors, which are difficult to stop and can release harmful radioactive material.
A fusion reaction produces around 4 million times more energy per weight than the chemical reactions that occur when fossil fuels such as coal and natural gas are burned, making it a clear alternative to these first-line energy sources. Fusion also uses very small amounts of starting material and can self-sustain future reactions by using the products of initial reactions. Unlike fossil fuels, hydrogen, the fuel for fusion, is the most abundant material in the universe and produces no greenhouse gases when consumed. These features make fusion energy safe, limitless, efficient, and clean.
How far away are we from using fusion energy?
There are research groups working towards fusion energy, all with different approaches in different states of progress. One such group attempting the technology described in this article is Massachusetts’ Commonwealth Fusion Systems. The scientists there hope that plasma-based fusion energy will be used to power homes by as early as 2035 given a successful test of the first ever 20T magnet of its kind just a few months ago. Their final design for commercial-grade equipment includes 18 of those high-field magnets arranged in a circle to act as the plasma bottle that confines the fast-moving particles. Their current research efforts now focus on demonstrating fusion using the tested 20T magnet, testing its limits, and modeling how the magnet may behave if any part of its system fails. Their next big hurdle after achieving plasma fusion? Refining the technology so the process generates more energy than it uses (Q>1). Considering the great leaps that this company and other researchers have made in the past two decades, the odds are high that they will achieve this next goal.
Brianna Alico is a graduate student in the Biological and Biomedical Sciences PhD program at Harvard University; her husband is a superconductor test engineer at Commonwealth Fusion Systems in Cambridge, MA and is the source of inspiration for this article.
Aparna Nathan is a fourth-year Ph.D. student in the Bioinformatics and Integrative Genomics Ph.D. program at Harvard University. You can find her on Twitter as @aparnanathan.
Cover image by Hans from pixabay
For more information:
- To learn more about the fusion energy sector, see this 2021 Nature article.
- To discover more about one company’s approach to fusion energy using high-field magnets, explore Commonwealth Fusion System’s website describing their research progress and plans.
- Check out this video by Commonwealth Fusion System’s CEO for a brief summary of the history of fusion energy.
- This CERN article on high-temperature superconductors and the magnets of the future provides a great summary of the development and applications of HTS in fusion.