In this blog post, we explore whether fusion energy could be the ultimate solution to the energy shortages and global warming challenges facing humanity.
Nuclear fusion is a reaction in which hydrogen atoms fuse under high temperatures and pressures to form a helium atom, releasing energy in the process. It is the source of solar energy that powers the Sun, which in turn supplies energy to over 7 billion humans and countless other living organisms. The hydrogen isotopes used as fuel in nuclear fusion reactions release a significant amount of energy during the process, which is governed by Einstein’s “mass-energy equivalence principle.” The mass of a single helium atom after the reaction is approximately 0.7% less than the combined mass of the four hydrogen atoms before the reaction; this difference in mass is called the “mass deficit.” This mass deficit is converted into energy during the fusion process. Power generation using such fusion reactions is about five times more efficient than fission, and just 500 grams of fuel can produce twice as much electricity as a Kori nuclear power plant. Furthermore, it is considered a clean energy source because it produces less radioactive waste and greenhouse gas emissions compared to other power plants. Furthermore, since there is enough fuel buried in the oceans and on the Earth’s surface to last humanity for 15 million years, scientists have been striving since the mid-20th century to control fusion reactions and use them as an energy source.
However, for a fusion reaction to occur, high temperatures and pressures are required so that hydrogen nuclei can overcome electromagnetic forces and fuse into helium nuclei. In the cores of stars like the Sun, the star’s own gravity solves this problem, but on Earth, special methods were needed to create such an environment. To address this, scientists devised two methods: magnetic confinement fusion and inertial confinement fusion. This article introduces the principles and characteristics of these two methods.
As the name suggests, magnetic confinement fusion is a method that uses magnetic fields to confine plasma. Although it initially began with long linear devices, the problem of energy loss at both ends led to the development of doughnut-shaped toroidal devices. Early toroidal devices used only toroidal coils to control the plasma, but this caused the plasma to drift within the toroid. To solve this, a method was developed to apply an additional magnetic field to the plasma inside the torus, causing the plasma flow to twist into a corkscrew shape. The tokamak, devised by Tamm and Sakharov in Russia in the early 1950s, and the stellarator, proposed by Lyman Spitzer in the United States, are prime examples of this technology. While the tokamak indirectly generates an additional magnetic field by inducing a current in the plasma through electromagnetic induction, the stellarator directly generates a magnetic field by adding helical coils—conductors twisted like a pretzel—to the exterior of the torus. Although the tokamak method faces difficulties in maintaining and controlling plasma currents stably over long periods, its simple structure has led to continuous research from the mid-20th century to the present. In contrast, despite the advantage of easier current control and maintenance, the stellarator experienced a long period of stagnation until the 1990s due to the complexity of its structure. However, thanks to current technological advancements, both tokamaks and stellarators are being actively researched around the world, and more complex devices are being constructed globally.
Inertial confinement fusion involves rapidly compressing and heating fuel to reach fusion conditions, then burning it before the fuel escapes. Because this method requires precisely striking a target with a powerful laser, it is also called “laser fusion,” and research has been conducted since the 1960s, led primarily by the United States, France, and the United Kingdom. Inertial confinement fusion occurs the moment a laser is fired at a small plastic pellet. When the laser is focused on the pellet, the fuel inside reaches fusion conditions, triggering a rapid fusion reaction that releases energy. However, due to technical limitations, the energy generated by the fusion reaction is currently much less than the energy used by the laser, making it less feasible than the magnetic confinement fusion method. Laser fusion is divided into indirect and direct methods, depending on how the laser is focused onto the pellet. The indirect method uses a cylindrical metal container (hollow) to concentrate energy onto the pellet. When the laser is focused on the metal cylinder, the metal emits intense X-rays, and within one-hundred-millionth of a second, the temperature at the center of the metal cylinder rises to 40 million K. This causes the pellet at the center of the cylinder to explode instantaneously, and as a result, the fuel inside the pellet is compressed to an ultra-high density, triggering a nuclear fusion reaction. However, this method has the problem of being very similar in principle to a hydrogen bomb. In fact, some studies have been accused of violating the Comprehensive Nuclear-Test-Ban Treaty or the Nuclear Non-Proliferation Treaty. Therefore, in countries such as Japan, where restrictions exist on the development of nuclear weapons-related technology, researchers are developing methods that focus the laser directly onto the pellet to melt and expand its shell, rather than using an indirect approach.
To summarize the content so far, magnetic confinement fusion uses magnetic fields to confine plasma to meet the conditions for nuclear fusion, and is divided into tokamaks and stellarators depending on the method used to generate the magnetic fields. In contrast, inertial confinement (laser) fusion aims to trigger a fusion reaction by instantly concentrating energy before the fuel disperses, and is classified into direct and indirect methods depending on the laser irradiation method. Although research into both of these methods began as weapons technology, similar to nuclear fission, research into fusion as an energy source proceeded through international cooperation organized by the International Atomic Energy Agency starting in 1961. In 1998, seven countries began collaborating to construct the International Thermonuclear Experimental Reactor (ITER) in Cadarache, France. Despite decades of effort by scientists, the commercialization of fusion power remains a difficult challenge. Currently, it is estimated that humanity will begin using nuclear fusion as an energy source around 2050; this is a massive and complex project requiring many nations to invest significant human resources and funding over an extended period. However, as nuclear fusion is the ultimate solution to global warming and energy shortages—the greatest challenges facing humanity in the 21st century—it requires the discovery and cultivation of talented individuals, as well as policy support with a long-term perspective.
