This blog post explores whether fusion energy could become the ultimate solution to the energy shortages and global warming challenges facing humanity.
Nuclear fusion is a reaction where hydrogen atoms fuse into helium atoms under extreme heat and pressure, releasing energy. It is the source of solar energy that powers the Sun, which sustains over 7 billion humans and countless other life forms. The hydrogen isotopes used as fuel in nuclear fusion release vast amounts of energy during the fusion process, adhering to Einstein’s ‘mass-energy equivalence principle’. The mass of one helium atom after the reaction is approximately 0.7% less than the combined mass of the four hydrogen atoms before the reaction. This mass difference is called the ‘mass deficit’. This mass deficit is converted into energy during the fusion process. Power generation using such nuclear fusion reactions is about five times more efficient than fission, enabling the production of twice the electricity of a nuclear power plant using only 500 grams of fuel. Furthermore, compared to other power plants, it produces less radioactive waste and greenhouse gas emissions, making it a clean energy source. Moreover, enough fuel to power humanity for 15 million years is buried in the oceans and on the Earth’s surface. Since the mid-20th century, scientists have endeavored to control nuclear fusion reactions for energy use.
However, for nuclear fusion to occur, extremely high temperatures and pressures are required—enough to overcome the electromagnetic force and fuse hydrogen nuclei into helium atoms. While the gravity of stars like the Sun solves this problem at their cores, Earth required special methods to create such conditions. To address this, scientists devised two approaches: magnetic confinement fusion and inertial confinement fusion. This article introduces the principles and characteristics of these two methods.
Magnetically confined fusion, as the name suggests, uses magnetic fields to confine the plasma. Initially developed in long linear devices, the problem of energy loss at the 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. Representative examples of this technology are the tokamak, devised by the Russians Tamm and Sakharov in the early 1950s, and the stellarator, proposed by the American Lyman Spitzer. While the tokamak indirectly generates the additional magnetic field by using electromagnetic induction to flow current through the plasma, the stellarator directly creates the magnetic field by adding a helical coil—a conductor twisted like a pretzel—outside the torus. Although the tokamak approach faces challenges 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. Conversely, despite the stellerator’s advantage of easier current control and maintenance, its structural complexity led to a long period of stagnation until the 1990s. However, thanks to current technological advancements, both tokamaks and stellerators are now actively researched worldwide, with increasingly complex devices being constructed globally.
Inertial confinement fusion rapidly compresses and heats fuel to reach fusion conditions, then ignites it before the fuel can escape. This method, requiring precise targeting of the target with powerful lasers, is also called ‘laser fusion’. Research has been led by the US, France, and the UK since the 1960s. The inertial confinement process occurs the moment lasers strike a small plastic pellet called a pellet. When the lasers converge on the pellet, the fuel inside reaches fusion conditions, rapidly triggering a fusion reaction that releases energy. However, due to technical limitations, the energy generated by the fusion reaction has so far been significantly less than the energy used by the laser, making it less feasible compared to magnetic confinement fusion. Laser fusion is categorized into indirect and direct methods based on how the laser is focused onto the pellet. The indirect method uses a cylindrical metal container (Hohlraum) to concentrate energy onto the pellet. When the laser is focused onto the metal cylinder, the metal emits intense X-rays, causing the temperature at the cylinder’s center to rise to 40 million K within one hundred millionth of a second. This causes the pellet at the cylinder’s center to explode instantaneously. The resulting recoil compresses the fuel inside the pellet to an ultra-high density, triggering a nuclear fusion reaction. However, this method has the problem of being very similar to the principle of a hydrogen bomb. Indeed, some research is alleged to violate the Comprehensive Nuclear-Test-Ban Treaty or the Nuclear Non-Proliferation Treaty. Consequently, countries like Japan, which face restrictions on nuclear weapons-related technology development, are instead developing a direct method. This involves focusing the laser directly onto the pellet to melt and expand its shell.
To summarize the content so far: Magnetic confinement fusion uses magnetic fields to confine plasma and meet fusion conditions, and is divided into tokamaks and stellarators based on the method of generating additional magnetic fields. In contrast, inertial confinement (laser) fusion aims to concentrate energy instantaneously to trigger fusion reactions before the fuel disperses. It is categorized into direct and indirect methods based on the laser irradiation approach. Both approaches began as weapons research, similar to nuclear fission. However, in 1961, international cooperation led by the International Atomic Energy Agency (IAEA) initiated fusion research as an energy source. In 1998, seven nations began collaborating to construct the International Thermonuclear Experimental Reactor (ITER) in Cadarache, France. Despite decades of scientific effort, commercializing fusion power remains a significant challenge. Currently, it is anticipated that humanity will begin utilizing nuclear fusion as an energy source around 2050. This represents a massive and complex project requiring sustained investment of manpower and resources by numerous nations over an extended period. However, nuclear fusion stands as the ultimate solution to the greatest challenges facing humanity in the 21st century: global warming and energy shortages. It necessitates the discovery and cultivation of talented individuals, along with policy support grounded in a long-term vision.
