In this blog post, we will look at whether nuclear fusion energy can be the ultimate solution to the energy shortage and global warming issues facing humanity.
Nuclear fusion is a reaction in which hydrogen atoms fuse at high temperatures and pressures to release energy as helium atoms, and it is the source of solar energy that provides energy to more than seven billion people and countless other living organisms. The isotopes of hydrogen, the fuel of the nuclear fusion reaction, release a lot of energy during the nuclear fusion process, and Einstein’s “mass-energy equivalence principle” is applied to this process. The mass of a helium atom after the reaction is about 0.7% smaller than the mass of four hydrogen atoms before the reaction, and this difference in mass is called “missing mass.” The loss mass is converted into energy during the nuclear fusion process. Power generation using this nuclear fusion reaction is about five times more efficient than nuclear fission, and only 500 grams of fuel can produce twice as much power as a nuclear power plant. It is also considered a clean energy source because it produces less radioactive waste and greenhouse gas emissions than other power plants. Moreover, there is enough fuel in the oceans and on the earth’s surface to last humanity 15 million years, so since the mid-20th century, scientists have been working to control nuclear fusion reactions and use them as an energy source.
However, in order for a nuclear fusion reaction to occur, a high temperature and pressure are required to overcome the electromagnetic force of the hydrogen nucleus and allow it to combine with the helium nucleus. In the core of a star like the Sun, the gravity of the star itself solves this problem, but on Earth, a special method was needed to create this environment. The two methods that scientists have devised to solve this problem are magnetic confinement nuclear fusion and inertial confinement nuclear fusion. This article introduces the principles and characteristics of these two methods.
Magnetic confinement fusion, as the name suggests, is a method of trapping plasma using a magnetic field. It initially started with a long linear device, but due to the problem of energy loss at both ends, a toroidal device was developed. In the early days, only toroidal coils were used as a means of controlling plasma in toroidal devices, which caused plasma to drift inside the toroid. To solve this problem, a method was developed to apply an additional magnetic field to the plasma inside the toroid to twist the flow of plasma into a twist shape. Tokamak, which was invented by Russian scientists Yakov Sakharov and Georgy Tamm in the early 1950s, and the Stellarator, which was proposed by American scientist Lyman Spitzer, are representative examples of such technologies. Tokamak uses electromagnetic induction to create an additional magnetic field indirectly by passing an electric current through the plasma, while the stellarator generates a direct magnetic field by adding helical coils of twisted conductors outside the torus. The Tokamak method has difficulty in maintaining and controlling plasma current stably for a long time, but it has been studied steadily from the mid-20th century to the present due to its simple structure. On the other hand, despite the advantages of easy current control and maintenance, the Stellarator suffered a long period of stagnation until the 1990s due to its complex structure. However, thanks to current technological advancements, both tokamaks and stellarators are being actively researched around the world, and more complex devices are being built around the world.
Inertial confinement fusion is a method in which fuel is rapidly compressed and heated to reach nuclear fusion conditions and then combusted before the fuel escapes. This method is also called “laser nuclear fusion” because it requires a powerful laser to accurately hit the target, and research has been conducted since the 1960s, mainly by the United States, France, and the United Kingdom. The inertial confinement method occurs the moment the laser is fired at the small plastic beads called pellets. When the laser is focused on the pellets, the fuel inside the pellets reaches the conditions for nuclear fusion, and at this point, a nuclear fusion reaction occurs at a rapid rate, releasing energy. However, due to technical limitations, the energy generated by nuclear fusion reactions is much less than the energy used in lasers, making it less feasible than magnetic confinement nuclear fusion. Laser nuclear fusion is divided into indirect and direct methods depending on how the laser is focused on the pellets. The indirect method uses a cylindrical metal container (holmium) to focus energy on the pellets. When the laser is focused on the metal cylinder, the metal emits powerful X-rays, and the temperature at the center of the metal cylinder rises to 40 million K in 100 millionths of a second. This causes the pellet to explode in a moment, and the reaction of nuclear fusion occurs as the fuel inside the pellet is compressed to an extremely high density in reaction. However, this method is problematic because it is very similar to the principle of hydrogen bombs. Some studies have actually argued that it violates the Comprehensive Nuclear Test Ban Treaty and the Nuclear Non-Proliferation Treaty. Therefore, some countries, such as Japan, which have restrictions on the development of nuclear weapon-related technologies, are developing a method of melting and expanding the shell by focusing a laser directly on the pellet instead of using an indirect method.
To summarize what has been said so far, magnetic confinement fusion uses a magnetic field to trap plasma to meet the conditions for nuclear fusion, and is divided into tokamaks and stellarators depending on the method of creating an additional magnetic field. In contrast, inertial confinement (laser) nuclear fusion aims to concentrate energy instantaneously to cause a nuclear fusion reaction before the fuel disperses, and is divided into direct and indirect methods depending on the laser irradiation method. Both of these methods began as weapons research, like nuclear fission, but in 1961, international cooperation under the auspices of the International Atomic Energy Agency led to the research of nuclear fusion as an energy source. In 1998, seven countries began working together to build the International Thermonuclear Experimental Reactor (ITER) in Cadarache, France. Despite decades of efforts by scientists, the commercialization of nuclear fusion power remains a challenge. It is expected that humanity will use nuclear fusion as an energy source around 2050, which is a huge and complex project that will require many countries to invest a lot of time and resources. However, nuclear fusion is the ultimate solution to the biggest problems facing humanity in the 21st century: global warming and energy shortages. It requires the discovery and cultivation of talented individuals and long-term policy support.
