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Tungsten has tested the readiness for thermonuclear reactors

This material is considered key to the success of existing projects fusion.

At the Institute of nuclear physics, Siberian branch of RAS developed methods of optical diagnostics of metal surface, allowing to study the cracking of tungsten under powerful heating in real time. It turned out that its dynamics differs markedly from that predicted theoretically. Relevant article published in Physica Scripta.

Many laboratories worldwide are studying the action of powerful streams of plasma on the materials. This has great practical meaning: resistance of the materials of the first wall of the vacuum chamber is a key problem in fusion reactors. The merging of nuclei is more effective at higher temperature, so it is expected that the Grand being built on the initiative of Russian nuclear scientists tokamak ITER (International Thermonuclear Experimental Reactor) plasma temperature will reach 150 million degrees Celsius.

In theory, it will hold a magnetic field, but in practice in the experimental reactor the inevitable uncontrolled plasma, albeit short-lived, but intense. Therefore, the most suitable material for a nuclear fusion reactor considered to be the tungsten metal, resistant to heat and radiation loads. During the pulse heating of the tungsten, and any other material that expands strongly, and then by cooling it shrinks and cracks.

To predict the behavior of tungsten under such outrageous loads, the researchers used an experimental stand of BETA (Beam of Electron for material Test Applications). Still in real-time to examine the powerful effects of the heating pulse was not possible — they produce parasitic illumination at the point of contact with tungsten, which illuminates the whole image. Therefore, in the new work, physicists used a powerful electron beam. When injected into the material he gives relatively little background light which interferes in the optical diagnostics. But to better understand what happens in heat stroke, additionally used the diagnostic laser. In the end, the researchers were able to achieve the parameters of the heating are similar with the alleged pulse of plasma in the ITER (duration of 300 microseconds, the power to ten gigawatts per square meter).

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It turned out that the process of cracking is much more complex than previously thought. Cracks in tungsten, contrary to expectations, can not appear during the heat exposure, and an unexpectedly long delay after it. Myself heat stroke lasted less than a millisecond, but the surface of tungsten is not cracked during the pulse, and a few seconds after him, when the metal has cooled down to room temperature. The new data will allow much more accurate to predict the behavior of this material in a fusion reactor.

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