Deuterium Retention in Carbon, Beryllium, and Carbon Layers on Titanium and Beryllium

In the context of plasma-facing walls in future nuclear fusion devices, a knowledge of the reaction mechanisms and properties of these materials is essential for operation and safety. The aim of the studies for this thesis was to investigate the effect of implanting ke V deuterium ions in various mixed and pure materials. To do so required an adaptation of the existing ultra-high vacuum experiment Artoss; the modified version of this apparatus allowed the detection of hydrogen isotopes, besides having an updated vacuum system where vacuum conditions with base pressures of less than 3 x 10-9 Pa were achieved. Using Artoss and another ultra-high vacuum device (XPS), clean samples of crystalline beryllium, highly-oriented pyrolytic graphite, and mixed materials consisting of beryllium and titanium substrates with carbon surface layers of less than 10 nm thickness were bombarded with 1 and 4 ke V deuterium ions. Deuterium retention in clean metallic beryllium was found to saturate at 2x 10 15 /cm2; beryllium samples prepared with carbon surface layers displayed higher hydrogen isotope retention. In addition to eroding the carbon surface layer, the deuterium ions carry the energy to modity the carbon surtace layer, creatmg metallIc carbIde phases. Carbon in its elementary form was found to erode at a significantly greater rate than carbon in the metallic carbide phases. The erosion behaviour of titanium carbide is in good agreement with computer simulations of a kinematic sputtering model, whereas the exponential erosion rate of elementary carbon suggests that chemical interactions play an additional important role. These findings suggest that beryllium, despite being a highly toxic material, is well suited as a first-wall material in future fusion devices, provided a high-quality vacuum can be consistently achieved. II Acknow ledgements I would like to thank my university supervisor, Prof. Brian Sealy, for agreeing to take me on as an external student, with my infrequent visits due to the long distance, and substitute communication via telephone and email. With great pleasure, I acknowledge the support, guidance and help of my local supervisor in Garching, Dr. Christian Linsmeier during the entire time of working on this thesis. His help, both work-related as well as socially (living in a foreign region: Bavaria), was always thankfully received. I greatly acknowledge working in the plasma-waIl-interactions PWW group at the "Max-Planck-Institut fUr Plasmaphysik". I thank all colleagues in the division for being who they are. In particular, I thank the head of …