Fusion Energy

　The energy of the stars shining in the night sky is due to the nuclear fusion reaction.The energy released when a nucleus collides with another nucleus and a new nucleus is created by a fusion reaction is one million times as much as the energy released by a chemical reaction. The sunlight that falls on the earth is also produced by the nuclear fusion reaction. A fusion reactor is an attempt to artificially control a fusion reaction and extract its enormous energy as electricity or heat. In order for us, and our children's children, and their children's children, to live peacefully for a long timecontinue to benefit from the development of science and live a comfortable and enjoyable life all over the world, research and development of fusion reactors is underway.
　　　　　　
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　From NASA's web site

ITER project

　Japan, Europe, the United States, Russia, China, South Korea, and India are collaborating to build the fusion experimental reactor ITER for the purpose of scientific and technical demonstration of fusion energy utilization in Cadarache, France. The first plasma will be ignited in 2025, and full-scale fusion experiments will begin in 2035.Isn't it an attractive research target for those who want to become scientific researchers in the future? Let’s be a world-leading researcher and lead the ITER project to success!
　　　
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　ITERのwebサイトより

Related research in our Lab.

• Understanding of the bred tritium behavior and development of the recovery system

　The fuels of fusion reactors are deuterium and tritium, which are isotopes of hydrogen. Hydrogen is abundant in nature, but tritium is almost absent. The fuel system that produces tritium by the reaction between lithium and the neutrons generated in the fusion reaction is being considered. Therefore, it can be said that "Fuel resources" are "deuterium" and "lithium", which are abundant in seawater.By devising tritium production method, we aim to produce more tritium than the tritium consumed in the fusion reaction. The produced tritium is referred to as "bred tritium", and the lithium compound is referred to as "tritium breeding material".There are two types of tritium breeding materials: "liquid breeding materials" that are used in liquid form and "solid breeding materials" that are used in solid form.The liquid breeding material has the excellent feature that it can be circulated as a fluid and can also act as a coolant by itself.
　In our laboratory, we are studying both liquid breeding materials and solid breeding materials, and we are conducting a wide range of research from basic research for understanding tritium behavior to development of tritium separation and recovery systems.Engineering equipment that produces tritium and recovers heat is referred to as a tritium breeding "blanket." The blanket is the most important device for utilizing fusion energy.

• Understanding of tritium behavior in plasma facing wall

　The fusion reaction occurs at the center of a high-temperature, high-density plasma generated in a large vacuum vessel. The plasma is tightly confined by the lines of magnetic force, but some of the high-energy particles are impingined to the plasma faing wall. Here, "plasma facing wall" consists of the wall on the plasma side of the blanket, which is referred to as "first wall", and the wall on the plasma side of the divertor, which exhausts helium ash generated in fusion reaction. Some of tritium and deuterium are implanted into the plasma facing wall as high-energy particles. Most of the implanted particles are re-emitted to the plasma side, but some of them diffuse and accumulate in the wall and also permeate into the coolant flowing through the pipe inside the wall. こAt this time, the　structure of the wall surface exposed to high particle-load and high heat-load is changed from the original structure by sputtering or melting. Some of the elements constituting wall that are emitted to the gas phase by sputtering or melting adhere to the wall and then deposited layer is formed.
　Fusion plasma experiments using graphite as the wall material revealed that a large amount of fuel hydrogen isotopes are incorporated into the deposition layer. This meant that some of the fuel supplied to plasma continuously accumulate in the walls without fusion reaction, that was a revire problem that threatened the realization of a fusion reactor.
　In our laboratory, we are working on the understanding of hydrogen isotope behavior in the deposition layer, focusing on tungsten, which is expected as a promising wall material to replace graphite.We also plan to study the effects of neutron irradiation on tritium behavior.

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