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Researchers at the GI Budker Institute of Nuclear Physics at the Siberian Branch of the Russian Academy of Sciences (INP SP RAS) has started testing a new coating from boron carboide for the walls of the International Experimental Thermonuclear Reactor (ITER) under construction in France.
Research has been reported in Nuclear Engineering International and explains that the team looked for a substance to withstand damage caused by plasma during a thermonuclear reaction.
The plasma in the tokamak is a toroidal vacuum chamber and finding a material for the first wall that meets all the requirements was difficult. Carbon was used in research for tokamaks to protect the walls but proved problematic because it can retain hydrogen isotopes and radioactive tritium.
Currently, tungsten and beryllium are used in the first wall of the camera in ITER, which can withstand high temperatures and is very light, but the dust from beryllium is toxic and is a strong carcinogen.
Head of the ITER center, Anatoly Krasolnikov has led a team that looked for alternative options for covering the wall of the tokamak, which needed to be heat-resistance, lightweight, with high thermal and electrical conductivity. This includes some types of ceramics which are typically used as an insulator.
The Lavrentyev Institute of Hydro dynamics SB RAS, Khristianovitch Institute of Theoretical & Applied Mechanics, and Tomsk State University of Management Systems & Radio Electronics were involved in the study.
A coating of special material was applied with a thickness of only tens of microns, and tests are being carried out at the BETA installation at INP SP RAS. During the tests, the material is subjected to thermonuclear pulse loads and a laser-powered thermal load from the plasma. Temperature absorbed head and degree of erosion is being tracked using a diagnostic system. The moment erosion begins can also be tracked which can cause roughness to change and can be identified with the subsequent loss of matter.
Research engineer Dmitry Cherepanov explained, “the purpose of the tests was to characterize the limit of the loads that our test martials can withstand during pulsed heating.”
“We have been developing neutron protection from boron carbide with Virial (St Petersburg) for a long time. Viral company is a manufacturer of equipment components of ceramic and cera-metallic materials,” said researcher Alexander Burdakov. “This substance is very durable, has relatively good thermal conductivity, and we test it under the impulse loads that are characteristic of tokamaks.”
Similar to light beryllium, boron carbide does not cause the walls to cool quickly, and it also is readily available. In using boron carbide there are two options as it can completely replace tungsten or be applied to tungsten walls as a protective coating.
As of now, the results from the BETA complex testing, the threshold values of loads at which ceramics begin to collapse are similar to tungsten. Tests also suggest boron carbine is competitive with tungsten carbide and beryllium coatings.
source：coatingsworld
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