In the course of plasma magnetic traps’ operation, erosion their walls’ occurs, and nano-dimensional films and dust particles are formed. Researchers at the Russian Scientific Center “Kurchatov Institute” assert: the dust can favorably influence the reactor’s operation.

A tokamak (a toroidal chamber with magnetic coils) is a closed magnetic trap intended for high-temperature plasma creation and confinement. Controlled thermonuclear fusion can be accomplished in such reactors – fusion of lighter nuclei that provides heavier nuclei and energy release. Plasma is the state in which all substances are transferred under strong heating (the temperature is measured by hundreds of millions of degrees). In plasma, not only bonds between molecules are destroyed (like under evaporation) but also bonds between atoms and even between atoms’ neuclei and electrons. Plasma consists of charged particles and, therefore, it can be retained by magnetic field. Under normal conditions, plasma should not touch the internal surface of tokamak but sometimes certain particles do reach the walls, thus causing erosion.

“The nanostructures being formed as a result of erosion of plasma-facing tokamak chamber elements mainly have a negative effect”, wrote specialists at the Kurchatov Institute  in the article about nanodust published at the “Physical Sciences Progress” journal. Nanostructures accumulate tritium – this causes damage to the reactor safety as this hydrogen isotope is radioactive, besides, its losses cause significant financial damage: the price of tritium is about 10 000 000 $/kg. Should water get into the chamber (in emergency situation), nanostructures can serve as a catalyst for its decomposition into oxygen and hydrogen, thus creating explosion hazard. Radioactive dust presence in the air represents danger for specialists during reactor opening.

Studying nanodust in tokamaks has demonstrated that the films being formed mainly consist of carbohydrates and tungsten. They can be smooth or possess a complicated relief. Nanoparticles can unite into the approximately 15-nm clusters or form a disordered structure. The hydrogen isotopes (deuterium and tritium) adsorption mechanism was studied on smooth films, and researchers suggested the thermodesorption method - deuterium and tritium removal from films under heating.

The researchers have found out that the dust being formed on the reactor chamber surface can also play a favorable role: it enables to support plasma discharge stability due to plasma density increase and plasma temperature decrease. Besides, the authors draw attention to complicated latticed nanostructures with large surface area, which are being formed from particles settling on the reactor surface. Probably, this by-product of reactor work will be used in the future to solve some other processing tasks.

Source of information: “Nanostructures in controlled thermonuclear fusion plants”,  V.I. Krouz, Yu.V. Martynenko, N. Yu. Svechnikov, V.P. Smirnov, V.G. Stankevich, L.N. Khimchenko, Uspekhi fizicheskikh nauk (Physical Sciences Progress), Vol. 180, #10, 2010, http://ufn.ru/ufn10/ufn10_10/Russian/r1010c.pdf

Further information: Yuri Vladimirovich Martynenko – specialist, Kurchatov Institute, e-mail: martyn@nfi.kiae.ru