Nuclear Fusion: The Next-Generation Energy Source

On the sun, enormous energy is generated by nuclear fusion reactions, where light atoms (hydrogen) collide and transform into slightly heavier atoms (helium). Nuclear fusion energy is anticipated as a next-generation energy source that, if realized, could significantly improve current energy problems. It offers several advantages: its fuel resources are abundant in seawater and virtually inexhaustible; it is inherently safe, as chain reactions do not occur in principle; it does not emit carbon dioxide; it is capable of large-scale power supply; and it does not produce high-level radioactive waste. For these reasons, research to utilize nuclear fusion energy for industrial purposes is being vigorously pursued worldwide, including projects like the International Thermonuclear Experimental Reactor (ITER), an international joint project among seven parties: Japan, the EU, the United States, Russia, China, South Korea, and India.

To initiate a nuclear fusion reaction, the hydrogen fuel is heated to over 100 million degrees Celsius, turning it into a plasma state (a gaseous state of charged particles where ions and electrons are separated). One of the major challenges in realizing nuclear fusion energy is how to protect the inner walls of the device from the high-temperature plasma. If the high-temperature plasma comes into contact with the walls, it can cause them to melt or become damaged. Therefore, it is necessary to sufficiently cool the plasma before it hits the walls. A proposed method involves injecting hydrogen gas or noble gases as impurities to cool the plasma through their interactions. However, unless the cooling is carefully controlled to occur only near the walls, the crucial nuclear fusion reaction itself will stop. To devise such control methods, it is necessary to understand the various interactions that occur among the plasma, atoms and molecules (hydrogen gas), impurities, and the inner walls of the device.

In our laboratory, we are conducting research aimed at achieving the compatibility of high-temperature plasma, where nuclear fusion reactions occur, and low-temperature plasma, which protects the walls, to realize nuclear fusion energy. To this end, we use numerical simulations to elucidate the various interactions and synergistic effects among plasma, atoms and molecules, impurities, and solid walls, and we are exploring methods to control them. Furthermore, similar physical phenomena are important in various other fields. We are applying the knowledge and numerical simulation techniques cultivated in fusion research to improve the performance of ion sources required for applications such as cancer therapy and particle physics research, in addition to heating fusion plasma.