[Zurück]

A. Golczewski, A. Kuzucan, K. Schmid, J. Roth, M. Schmid, F. Aumayr:
"Ion - induced erosion of tungsten and a-C:H surfaces studied by a sensitive quartz-crystal-microbalance technique";
Poster: 18th Intern. Conf. on Plasma-Surface-Interaction (18th PSI), Toledo/Spain; 27.05.2008; in: "Book of Abstract, 18th Intern. Conf. on Plasma-Surface-Interaction (18th PSI)", (2008), S. 219.

Utilizing a highly accurate quartz crystal microbalance (QCM) setup [1, 2] we study erosion of as well as implantation, re-diffusion and retention in tungsten and a-C:H surfaces under impact of singly and multiply charged ions. The material of interest is coated onto a SC-cut quartz crystal and the frequency change due to mass loss (sputtering, desorption) or mass gain (implantation, adsorption) during and after bombardment with fusion relevant ions is determined. Our setup is capable of detecting mass-changes as small as 10-6 µg/s, which corresponds to a removal (or deposition) of only 10-3 monolayers/s. Ion species, charged states and impact energies are selected to be as plasma-wall-interaction relevant as possible. With this setup we have determined total sputtering yields for impact of D+, Cq+ (q= 1 - 4) and Arq+ (q=1 - ?) on polycrystalline tungsten and a-C:H surfaces at impact energies ranging from typ. 100 eV up to a few keV. In contrast to deuterium projectiles, considerable sputtering yields of tungsten by carbon and in particular Ar ions (maybe used as an impurity introduced into the plasma for radiative edge cooling) have been found.
During irradiation of tungsten by low energy D+ ions (with impact energies close to the sputtering threshold) a complex and time-dependent frequency response of the QCM was found in our experiments. These data can be explained by a combination of mass increase due to deuterium implantation in tungsten and mass loss due to sputtering and re-diffusion of deuterium out of tungsten. Switching the ion beam on and off shows a transient behavior before a state of equilibrium between the different processes is reached. Since the measurements are performed in-situ during and after ion bombardment, implantation and diffusion of deuterium in tungsten can be studied in real time. Experiments with high deuterium-fluxes on plasma-sprayed tungsten are presently under way and promise important insight into the process of accumulation of deuterium in tungsten.

* golczewski@iap.tuwien.ac.at

[1] G. Hayderer et al. Rev. Sci. Instrum. 70 (1999) 3696
[2] G. Hayderer et al. Phys. Rev. Lett. 86 (2001) 3530