Boron Powder Prevents Tungsten from Immersing, A Safer "Artificial Sun"

Scientists at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have discovered a way to use insulating boron powder to isolate tungsten from the plasma, making the tokamak nuclear fusion reactor safer. Related research results have been published in the International Atomic Energy Agency (IAEA) academic journal Nuclear Fusion.

Nuclear fusion is the energy that drives the sun and stars, combines light elements in the form of plasma, the hot, charged state of matter composed of free electrons and atomic nuclei, that generates massive amounts of energy. Scientists are seeking to replicate fusion on Earth for a virtually inexhaustible supply of power to generate electricity.

The Tokamak device is a ring-shaped nuclear fusion device commonly known as an "artificial sun". In it, an extremely hot, charged plasma constrained by an electromagnetic field rotates and produces almost unlimited energy. However, the plasma in this device is easy to volatilize. Particles escaping from the plasma with the temperature of the sun will react with the material surrounding the tokamak, causing everything around the device in great danger. Therefore, it is important to ensure that the plasma of the Tokamak nuclear fusion device is not affected by impurities.

The tokamak is one of several types of magnetic confinement devices being developed to produce controlled thermonuclear fusion power. As of 2016, it is the leading candidate for a practical fusion reactor. Apply a layer of boron to the plasma-facing side of the Tokamak device. This process is called "boronization". Boron powder prevents a tungsten element from immersing in the plasma through the wall of the Tokamak device, cooling the plasma particles to reduce the reaction efficiency of nuclear fusion.

Tungsten owns the advantages of high melting point, high thermal conductivity, low physical sputtering rate, high sputtering threshold energy, low fuel retention, and low neutron activation. It is the primary choice for plasma-oriented materials (PFM) infusion experimental reactors and demonstration reactors. In Tokamak, to obtain a pure thermonuclear fusion plasma, impurities must be effectively controlled. The drawing of impurities is mainly to control the generation of impurities on the wall surface. The role of the tungsten diverter is to isolate the plasma from the first wall and shield the inflowing impurities as a metal in direct contact with the high-temperature gas.

Powder technology could also help scientists develop simpler and safer forms of plasma reactions called low-density plasmas. Low density can suppress the instability of the plasma by magnetic pulses, creating a wide range of controlled and safer plasma conditions.

Lunsford and the other scientists in the PPPL group hope to conduct experiments to determine where, exactly, the material goes after it has been injected into the plasma in the future. Physicists currently hypothesize that the powder flows to the top and bottom of the tokamak chamber, the same way the plasma flows, "but it would be useful to have that hypothesis backed up by modeling so we know the exact locations within the tokamak that are getting the boron powder layers," Lunsford said.

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