Interaction of Deuterium Plasma with pre-nitrided Tungsten Surfaces

 

Experiments in the tokamak ASDEX Upgrade have shown that the addition of nitrogen to the plasma reduces the power flux to the wall and at the same time improves the plasma performance. However, nitrogen from the plasma is implanted into the tungsten surfaces and becomes chemically bound. This bound nitrogen influences plasma-surface-interaction processes and hydrogen retention in the wall material.

The interaction of nitrogen-containing tungsten surfaces (WNx) with hydrogen plasmas and their influence on hydrogen retention was investigated in laboratory experiments by Gao Liang in the frame of his PhD thesis at IPP.

<p>Confocal laser scanning microscope image of a tungsten surface after deuterium implantation. The right-hand side of the sample was covered with a 100&nbsp;nm thick WN<sub>x</sub> layer prior to D implantation. The pure tungsten surface (left) shows strong blistering (formation of gas-filled cavities underneath the surface), while no blisters occur on the WNx-covered half (right).</p> Zoom Image

Confocal laser scanning microscope image of a tungsten surface after deuterium implantation. The right-hand side of the sample was covered with a 100 nm thick WNx layer prior to D implantation. The pure tungsten surface (left) shows strong blistering (formation of gas-filled cavities underneath the surface), while no blisters occur on the WNx-covered half (right).

[less]

One important result is the finding that nitrogen implantation into tungsten strongly suppresses hydrogen diffusion.

At 300 K the diffusion of H in WNx is negligible and at 600 K it is still much lower than in pure W.

Additionally he developed a refined method to determine the deuterium depth profile at surfaces with significantly improved depth resolution.

With this work L. Gao graduated at the Ruhr University Bochum in January 2016.

 

L. Gao et al., Nuclear Fusion 56, 016004 (2016),
http://dx.doi.org/10.1088/0029-5515/56/1/016004

L. Gao et al., Physica Scripta T159, 014023 (2014),
http://dx.doi.org/10.1088/0031-8949/2014/T159/014023

 
loading content
Go to Editor View