In order to realize nuclear fusion in power plants, it is necessary to stably confine the plasma of more than 100million degrees Celsius to a magnetic field and maintain it for a long time. The research team led by Naoki kenmochi, Katsumi IDA and tokihiko tokuzawa, associate professors of the National Institute of Fusion Science (NIFS) of the National Institute of Natural Sciences (nins) of Japan, and in cooperation with Professor Daniel J. den Hartog of the University of Wisconsin in the United States, using an independently developed measuring instrument, it was found for the first time in the world that when heat escapes in the plasma of a large spiral device (LHD), Turbulence moves faster than heat**
One of the characteristics of this turbulence makes it possible to predict the change of plasma temperature. It is expected that the observation of turbulence will lead to the development of a real-time method to control plasma temperature in the future.
In a high temperature plasma confined by a magnetic field, "turbulence" is produced, which is a flow with vortices of different sizes. This turbulence causes the plasma to be disturbed, the heat of the confined plasma flows outward, and the plasma temperature drops. In order to solve this problem, it is necessary to understand the characteristics of heat and turbulence in plasma. However, the turbulence in plasma is very complex, and researchers have not yet achieved a comprehensive understanding of it. In particular, how the generated turbulence moves in the plasma has not been well understood, because it requires the instrument to measure the time evolution of micro turbulence with high sensitivity and high spatial-temporal resolution.
A "barrier" can be formed in the plasma to prevent heat from being transmitted from the center to the outside. The "barrier" forms a strong pressure gradient and generates turbulence in the plasma. Associate professor kenmochi and his research team have developed a method to break this barrier by designing a magnetic field structure. This method enables researchers to focus on the heat and turbulence that flow vigorously when the barrier is broken, and study their relationship in detail. Then, using electromagnetic waves of various wavelengths, researchers measured the changes of temperature and heat flow of electrons and millimeter level small turbulence with the highest accuracy in the world. Before that, it was known that heat and turbulence moved at almost the same time at the speed of 5000 kilometers per hour, about the speed of an aircraft, but this experiment led to the first discovery in the world that turbulence moved before heat at the speed of 40000 kilometers per hour. The velocity of this turbulence is close to that of a rocket.
Naoki kenmochi said, "this research has greatly advanced our understanding of turbulence in fusion mass. The new characteristic of turbulence, that is, its moving speed in plasma is much faster than heat, indicates that we may be able to predict the temperature change of plasma by observing and predicting turbulence. In the future, on this basis, we are expected to develop a method to control the plasma temperature in real time."
The study was published in scientific report 》In magazines.