To build a fusion power plant, a plasma of more than 100 million degrees Celsius must be stored in a magnetic field and kept there for an extended period. Using measuring instruments developed independently and with the cooperation of Professor Daniel J. den Hartog of the University of Wisconsin, USA, a research group from the National Institute for Fusion Science (NIFS), National Institutes of Natural Sciences (NINS), Japan, discovered for the first time that turbulence moves faster than heat when heat escapes in plasmas in the Large Helical Device (LHD).
One feature of this turbulence allows for predicting changes in plasma temperature, and it is envisaged that further observations of turbulence will lead to the development of a system for real-time control of plasma temperature.
“Turbulence,” defined as a flow with vortexes of varying diameters, is formed in high-temperature plasma contained by a magnetic field. This turbulence disturbs the plasma, causing heat from the confined plasma to move outward, reducing plasma temperature.
However, turbulence in plasmas is so intricate that scientists have yet to comprehend it fully. The movement of created turbulence in plasma, in particular, is poorly understood since it necessitates sensors capable of measuring the time evolution of slight turbulence with great sensitivity and exceptionally high spatiotemporal resolution.
Assistant Professor Kenmochi and his research team have devised a magnetic field structure to overcome this obstacle. This technology allows us to investigate the heat and turbulence that flow furiously when the barriers breach in detail. Previously, heat and turbulence were known to travel practically concurrently at 5,000 kilometers per hour, roughly the speed of an airliner. Still, this experiment resulted in the world’s first finding of turbulence moving ahead of heat at 40,000 kilometers per hour. This turbulence moves at the speed of a rocket.
According to Assistant Professor Naoki Kenmochi, this discovery has significantly increased their knowledge of turbulence in fusion plasmas. The new property of turbulence that moves considerably quicker than heat in plasma suggests that scientists may be able to forecast plasma temperature changes by watching predictive turbulence. Based on this, they want to create ways to control plasma temperatures in real-time in the future.
