Nuclear Fusion 55 - DIII-D National Fusion Facility Develops New Technique o Cool Magnetically Confined Plasma

Nuclear Fusion 55 - DIII-D National Fusion Facility Develops New Technique o Cool Magnetically Confined Plasma

        Sometimes commercial nuclear fusion seems like the end of the rainbow. It was always “forty years” away no matter how much time passed. Today at least six companies in the U.S. alone are working on practical nuclear fusions systems and some say they are only ten years away from commercial reactors.
       One of the most popular approaches for nuclear fusion is to compress and heat a plasma to the point where the atoms fuse and release energy. This approach is very challenging and there are a lot of variables that have to be manipulated to keep the plasma safely confined. If the plasma escapes the control of the magnetic confinement, it can quench the fusion reaction and even damage the containment vessel if it is not brought back under control quickly.
       Heat from escaping plasma can melt the walls of the containment vessel, large erratic electrical currents can result in physical forces that can cause damage, and runaway high energy electron beams can cause serious localized damage. One way to prevent such damage is to inject material into the plasma that causes the plasma energy to uniformly radiate away. The problem with this approach is that it is difficult to get the injected material to the center of the plasma before some disruption occurs. If the researchers can get the injected materials into the center of the plasma, then the plasma can be cooled and disruptions can be stopped.
       The DIII-D National Fusion Facility (DNFF) is part of a national effort to generate magnetically confined nuclear fusion. The facility is located in San Diego and is operated by General Atomics for the U.S. Department of Energy. The DIII-D is a research tokamak that has been operated at the facility since the late 1980s.
       Researchers at the DNFF have just demonstrated a new technique to cool magnetically confined plasma before disruptions occur. The first step is the creation of a pellet of boron powder enclosed in a thin diamond shell. Then the pellet is sent into the center of the confined plasma at a speed of four hundred and fifty miles per hour. This gets the pellet deep into the plasma where the diamond shell disintegrates and releases the boron dust where it will have the maximum desired effect.
       This new technique could have a profound effect on regulating confined plasmas for the generation of nuclear fusion. It can potentially solve three major problems with confined plasmas. First, it efficiently, quickly and safely radiates away excess heat in the plasma. Second, it reduces the forces exerted by the plasma on the physical containment vessel. And, third, it prevents the formation of energetic electron beams.
       Richard Buttery is the Science Director for the DNFF. He said, “Shell pellets offer the potential of dealing with all three facets of the challenge, eliminating risk of device harm.” So far, the technique has only been demonstrated on a small research tokamak. In the future, the team will work on improving the design of the diamond shell that carries the boron dust so that it can be used to cool reactor-class plasmas in bigger tokamaks.