In this blog post, we’ll use the metaphor of a “sun-filled doughnut” to explore the principles of nuclear fusion power, the structure of a tokamak, the advantages of nuclear fusion power, the challenges that must be overcome for commercialization, and the latest research trends.
The donuts we eat contain a wide variety of ingredients. But what if, one day, you bought a donut and found the sun inside? It may sound like a wild fantasy, but what if this very “donut” held the key to radically transforming humanity’s future?
The Sun releases enormous amounts of energy through nuclear fusion reactions. Although only a tiny fraction of that energy reaches Earth, even that small amount is enough to sustain the Earth’s ecosystem and human civilization. So, if we could safely replicate the nuclear fusion reactions occurring inside the Sun here on Earth, wouldn’t that open up a new path to solving the energy problems that have long plagued humanity?
Of course, bringing the actual Sun here is physically impossible. Instead, scientists have turned their attention to plasma—often referred to as the “fourth state of matter”—as a medium capable of recreating an environment similar to that inside the Sun. The device developed to stably confine this ultra-high-temperature plasma is the doughnut-shaped tokamak. The name “tokamak” is derived from the Russian term “Toroidalnaya Kamera Magnitnymi Katushkami” (a doughnut-shaped vacuum chamber using magnetic coils). It is a device that confines plasma—the fusion fuel—inside a hollow, doughnut-shaped vacuum chamber to trigger a reaction, performing a function similar to that of a reactor in fission power generation.
The structure of a tokamak is organized around two primary axes: the toroidal direction, which runs along the circumference of the doughnut, and the poloidal direction, which runs along the cross-section of the doughnut. Various devices are complexly arranged within the tokamak, including superconducting magnets that generate powerful magnetic fields to prevent the ultra-high-temperature plasma from touching the vessel walls, a central solenoid coil that generates the plasma current, and a vacuum system that maintains an ultra-high vacuum inside the vessel.
The process of nuclear fusion occurring in a tokamak is often compared to a microwave oven. Of course, the actual principles are much more complex, but there are similarities in that both use strong electromagnetic waves from outside to heat matter. After injecting deuterium and tritium into the tokamak, the fuel is heated to ultra-high temperatures of over 100 million degrees Celsius using microwaves, neutral particle beams, and radiofrequency heating devices, causing it to enter a plasma state. Subsequently, the D-T nuclear fusion reaction—in which deuterium (D) and tritium (T) fuse—occurs, producing helium and high-energy neutrons. During this process, a very small amount of mass is converted into energy, and according to Einstein’s mass-energy equivalence principle (E=mc²), a massive amount of energy is released. The ultimate goal of nuclear fusion power generation is to reliably harness this energy for electricity production.
Nuclear fusion power generation offers several groundbreaking advantages compared to conventional power generation methods. First, deuterium—the fuel—can be obtained from seawater, and tritium can be produced using lithium, making the long-term availability of fuel highly likely. Consequently, this can significantly alleviate the problem of energy resources being concentrated in specific countries. Furthermore, although some structural components become radioactive due to neutrons during the fusion process, the volume of radioactive waste and the burden of managing it are relatively lower than in fission power generation, which produces high-level radioactive waste over the long term. Above all, since nuclear fusion reactions can only be sustained under very specific conditions—namely, ultra-high temperatures and powerful magnetic fields—the plasma cools naturally and the reaction stops if an anomaly occurs. Consequently, it offers inherently higher safety than fission power generation, where a chain reaction continues.
While nuclear fusion power is thus a highly attractive future energy source, there are still numerous technical challenges that must be overcome before it can be commercialized. First, heat- and radiation-resistant materials capable of withstanding plasma environments approaching hundreds of millions of degrees and high-energy neutrons over long periods must be developed. Furthermore, to confine the plasma stably, powerful magnetic fields must be maintained for extended periods, which necessitates superconducting magnet technology capable of operating at extremely low temperatures. These fields of materials engineering and superconducting technology remain key areas of active research worldwide.
Furthermore, the inherent instability of plasma itself poses a major challenge. Various forms of instability can occur within plasma, causing it to oscillate or partially collapse; in severe cases, this can lead to a “disruption,” where the entire plasma comes into contact with the vessel wall. Since these phenomena not only reduce output stability but can also lead to damage to the device, they are considered one of the most critical areas of research for commercialization. Currently, research institutions around the world are continuously conducting research to minimize these instabilities by utilizing AI-based control technologies and high-performance simulations.
In South Korea, world-class fusion research is being conducted primarily through KSTAR (Superconducting Fusion Research Device), operated by the Korea Institute of Fusion Energy. KSTAR continues to break records for maintaining ultra-high-temperature plasma stably over long periods, playing a crucial role in securing the technology for commercial fusion power. Internationally, the International Thermonuclear Experimental Reactor (ITER) project—involving South Korea, the European Union (EU), the United States, Japan, China, India, and Russia—is under construction in France. Although ITER has experienced some delays compared to the original schedule, it continues to move forward as the world’s largest international collaborative research project aimed at verifying the engineering feasibility of fusion power generation. Following this, a phased development plan is in place, leading from a demonstration power plant (DEMO) to a commercial fusion power plant.
We are now holding a “doughnut” that will change the future. It may still take quite some time before we can take that first bite. However, humanity is already steadily moving forward, one step at a time, toward the monumental goal of nuclear fusion. If the day ever comes when this “donut containing the sun”—capable of providing clean, safe, and virtually limitless energy—becomes part of our daily lives, it will be recorded as one of the greatest turning points in the history of energy.
