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| Fig. 1: Project KSTAR (Source Wikimedia Commons) |
Nuclear fusion is a sequence of two or more atomic nuclei coming together to form one or more different nuclei and subatomic particles. The difference in mass after the reaction is transferred to release of energy. Fusion of light-weighted elements generally results in exothermal process, while that of heavy elements in endothermic process. Hence the lighter elements, such as hydrogen and helium, are more suitable for obtaining energy from nuclear fusion. An example of such found in nature is the Sun, which is a natural fusion reactor that fuels the lives and nature on earth.
Current civilizations across the world meet their demand for energy from various sources, some of which includes fossil fuels, reusable energy, and nuclear fission reactions. Nuclear fusion is not yet an option. However, researchers across multiple nations are working in conjunction to develop the technology to use nuclear fusion as another source of energy. One of the products of the most recent development is KSTAR, an experimental research reactor in Korea.
The nuclei most feasible for nuclear fusion at the current stage are the isotopes of hydrogen, deuterium (D) and tritium (T). In a fusion reactor, deuterium and tritium are accelerated toward each other toward collision. The resulting reaction generates neutrons, which are absorbed by lithium that surrounds the core. The absorbed energy is translated into heat, which is then used to run the generator.
One of the biggest difficulties is maintaining the temperature high enough for the D-T fusion reaction to take place, and hold it for a sufficient amount of time to collect energy. In addition, nuclear fusion has lower power density output than nuclear fission. Heat yield for a fusion reaction is 70 times less than that of a fission. Although D-T fusion generates energy over four times as much as that from uranium fission on a mass basis, fission reaction uses solid uranium rods for fuel while fusion uses thermonuclear plasma. This would cause the fusion reactors to be bigger and more costly than those of nuclear fission.
There are many approaches to overcome the difficulties with maintaining high temperature, low density, and sufficient time to capture energy. For the interests of this paper, we will focus on two prominent approaches - magnetic confinement and inertial confinement.
Magnetic confinement fusion applies magnetic field at sufficiently high pressure and pressure to confine D-T plasma. [1] One of the most prominent forms of MCF is a toroid, which is a round circular form shaped like a doughnut that keeps the plasma cycling without touching the container. An example of a toroid confinement system is a tokamak, which traps the plasmid in side a toroid using strong magnetic field. [2] Its walls absorb the energy produced from atomic fusions within, which is used to operate the generator for electricity.
Building a nuclear fusion reactor is a complicated process. To reduce the research strain that would be imposed on a single country, a group of industrial nations have come together to collaborate on the project together. Of many multinational efforts, one of the organizations is ITER. Established in 2006, ITER is working on a collaboration project to build the world's largest tokamak. The members of ITER include China, India, Japan, Korea, Russia, the US, and Europe. The ITER Tokamak Complex is largely composed of three different buildings: Tritium and Diagnostic buildings, and the Tokamak itself, composed of vacuum vessel sectors, central solenoid, cooling water systems, and ITER magnets. [3] Considering the immense size of the project, each member of ITER specializes in one or few aspects of ITER Tokamak. This is not only to expedite the research progress, but also to allow each country to undergo technological advances in their specialities.
As one of the members of ITER, Korea has built an experimental tokamak named Korea Superconducting Tokamak Advanced Research (KSTAR). Fig. 1 shows the actual photo of the reactor. A project started early in 1995, KSTAR has allowed researchers to better understand the mechanisms required for nuclear fusion reactions. Technology and knowledge obtained from KSTAR will be of much importance to the development of the ITER tokamak.
One of the biggest difficulties of nuclear fusion is to keep the temperature high enough to maintain plasma inside reactors. To overcome this issue researchers are looking into tokamaks surrounded by strong magnetic field to keep plasma contained. [4] A research reactor, KSTAR, serves the main purpose of testing tokamak's limits in its capacity. It has a major radius of 1.8m, and is composed of two systems: TF system and PF system. TF system is composed of 16 TF coils that are electrically connected to create magnetic fields of 7.2T in magnitude. PF system is consisted of eight central coils in the central solenoid and six outer PF coils to compose the magnet system One disadvantage is its energy consumption - as a research reactor, it uses 154kV, 100MVA of electricity. [5]
For now, KSTAR may only be a research reactor, but its improvements are promising. The knowledge and experience obtained from KSTAR will supply researchers with knowledge and technology needed to make the ITER tokamak, which will make the world is one step closer to harnessing nuclear fusion as a reliable source of energy.
The sun is the primary source of energy for the lives and ecosystem on earth. Its energy comes from nuclear fusion reactions; the capabilities to harness its power on ground would be a remarkable feat not only for the humankind, but also for nature suffering from excess usage of traditional sources of energy. Although current technological difficulties have yet allowed a full exploitation of this technology today, a steady progress from multinational collaboration will one day open new doors for future civilizations and humankind.
© Simon Kim. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] V. Goeler et al., "Studies of Internal Disruptions and m=1 Oscillations in Tokamak Discharges with Soft X-ray Techniques," Phys. Rev. Lett. 20, 1201 (1974).
[2] M. Kikuchi, "A Review of Fusion and Tokamak Research Towards Steady-State Operation: A JAEA Contribution," Energies, 3, 1741 (2010).
[3] D. Combescure et al., "Structural Analysis and Optimization of the ITER Tokamak Complex," Transactions of the 21st Conference on Structural Mechanics in Reactor Technology, SMiRT 21, X-3A/3 (2011).
[4] A. Hassen et al., "Structural, Magnetic, and Electric Properties of Dy1-xSrxCoO3-δ (0.65≤x≤0.90)," J. Appl. Phys. 102, 123905 (2007).
[5] J. Bak et al., "Current Status of the KSTAR Construction," Cryogenics 47, 356 (2007).
