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In nuclear fusion research installations, the walls of the vacuum chamber are coated to prevent the contamination of the plasma with metallic impurities, as this would cause energy losses. The material chosen for this coating is a film of amorphous carbon with hydrogen content (a-C:H). Laboratory experiments were carried out with the aim of studying the permeation of hydrogen through such a coating and also the interaction between the hydrogen and the coated wall. Along with measurements with pure gaseous phase hydrogen, the low-energy flow of hydrogen ions onto the wall of a tokamak fusion research installation was simulated. The results indicated that within the a-C:H layer free hydrogen atoms are considerably less mobile than molecules. On bombardment of the layer with energy-laden particles from a radio frequency glow discharge, hydrogen was released on the primary side - three hundred times the quantity of hydrogen that permeated. Impacts result in the formation of free hydrogen atoms out of the surplus of bonded hydrogen within the coating. These free atoms recombine with each other as well as with hydrogen and deuterium atoms which have penetrated the layer and are released into the chamber. The knowledge acquired in these laboratory experiments can be applied directly to the current operation of fusion research installations such as TEXTOR.

Additional information

Authors: PILLATH J, Institut für Plasmaphysik, Kernforschungsanlage Jülich GmbH, Jülich (DE)
Bibliographic Reference: Report: Jül-2292 DE (1989) 153 pp.
Availability: Available from Zentralbibliothek der Kernforschungsanlage Jülich GmbH, Postfach 1913, 5170 Jülich (DE)
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