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May 27, 2013
The Mysteries of LHD Plasma Seen through a High-Speed Camera: Measuring Plasma through Images

In the Large Helical Device (LHD) we are observing and measuring the conditions of plasma through high-speed cameras. Compared to video cameras sold at stores that photograph at a speed of 30 frames per second, because a high-speed camera can photograph at more than 100,000 frames per second, not only can we observe in detail the conditions of plasma, we also can discover new phenomena from the mysterious images. Recently, photography by high-speed cameras has been used on television science programs. Perhaps you have seen images that have been stretched over time to show a phenomenon that occurred in but a moment. And the milk crowns caused by the dripping of water hitting the surface and the flapping of a hummingbird’s wings have reached your eyes, too. Here we will introduce several interesting features of LHD plasma captured by a high-speed camera.

  1. An Ejecting Blob of Plasma

    Plasma is confined by the magnetic field container. But depending upon conditions, part of the low-temperature plasma edge area sometimes leaks outside from gaps in the magnetic field container. When photographed by a high-speed camera, the plasma becomes a blob and it is observed intermittently ejecting from the periphery. Because this plasma blob has a small amount of energy it does not greatly influence the confinement of plasma. But using measurements from the images taken by the high-speed camera, we are endeavoring to clarify the generation mechanisms of this interesting phenomenon.

  2. Will an Asteroid Space Probe Plunge into Plasma?

    In order to investigate the behavior of impurities in plasma, small round impurity pellets of steel or carbon less than several millimeters in diameter are injected from outside into the plasma at the high speed of several hundred meters per second. When photographing this situation using a high-speed camera, a situation is photographed in which the impurities injected into the plasma melt and those disappear brightly. Seeing this makes one think of the asteroid space probe Hayabusa when it returned to Earth and the sight of the brightness that was measured upon re-entry into the Earth’s atmosphere. Through a high-speed camera, by measuring in detail the places where the impure pellets melted and those conditions, we are specifying where those impurities were generated and analyzing in detail the behavior of impurities in plasma.

  3. Measuring Shooting Stars in the Plasma Surface

    Fine dust is generated on the wall of the vacuum vessel and floats in the vicinity of the plasma. Using a high-speed camera, after the dust enters the plasma, the bright conditions when the dust melted were measured. This is just like the fine dust floating in outer space near the earth that appears to be a shooting star when it enters the earth’s atmosphere through the earth’s gravitation. Typically, the shooting stars that appear in the night sky draw a straight line and then disappear. But shooting starts measured on the surface of LHD plasma sometimes draw a large curve and sometimes divide into two with each moving in opposite directions just like a UFO moves. Using image measurements from a high-speed camera we are clarifying the odd behavior of dust in plasma.

  4. Discovering a Large Serpent in Japanese Fish Paste Cake

    When impurities enter the plasma such as through impurity pellets in large numbers, the plasma often is cooled and disappears. When conditions of that disappearance are closely analyzed through a high-speed camera, we have learned that at the arrival of large quantities of impurities in the plasma the temperature of the central area falls dramatically and that the plasma enters a condition similar to that of a Japanese fish paste cake in having no middle core. We have learned that, subsequently, after some period of time, a belt of light that resembles a winding snake appears and that the light moves while revolving around the empty inner part of the fish paste cake. Why this mysterious shape of a belt of light is formed is an extremely interesting phenomenon in terms of physics.