Filters

20202

More filters

2021 - 20222
Reset filters

Settings

Author: Schäfer, J. × Type: Article ×

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Influence of dielectric thickness and electrode structure on the ion wind generation by micro fabricated plasma actuators
    (Bristol : IOP Publ., 2020) Hink, R.; Pipa, A.V.; Schäfer, J.; Caspari, R.; Weichwald, R.; Foest, R.; Brandenburg, R.
    Surface dielectric barrier discharges are investigated in order to explore the combined effects of barrier thickness and microstructure of the exposed electrode on the ion wind generation. Actuators with straight and structured high voltage electrodes with characteristic sizes of 200 and 250 µm and dielectric thicknesses of 0.5, 1 and 2 mm are compared. It is observed that: i) actuator efficiency of ion wind generation strongly depends on the applied voltage amplitude; ii) operation voltage depends on the dielectric thickness logarithmically; iii) electrode microstructure slightly increases the dynamic pressure (few percent in maximum), however the effect decreases with thicker dielectrics and smaller electrode structures; iv) the pattern of the most intensive discharge parts as well as the dielectric erosion repeats the regular structure of the electrodes down to 200 µm. Several identical samples are tested during different days to estimate the impact of the air humidity and the degradation of the dielectric. The microscale precision of the sample manufacture was accomplished by a commercial facility for printed circuit boards. © 2020 The Author(s). Published by IOP Publishing Ltd.
  • Thumbnail Image
    Item
    Preparation, analysis, and application of coated glass targets for the Wendelstein 7-X laser blow-off system
    (Melville, NY : American Inst. of Physics, 2020) Wegner, Th.; Geiger, B.; Foest, R.; Jansen van Vuuren, A.; Winters, V. R.; Biedermann, C.; Burhenn, R.; Buttenschön, B.; Cseh, G.; Joda, I.; Kocsis, G.; Kunkel, F.; Quade, A.; Schäfer, J.; Schmitz, O.; Szepesi, T.
    Coated glass targets are a key component of the Wendelstein 7-X laser blow-off system that is used for impurity transport studies. The preparation and analysis of these glass targets as well as their performance is examined in this paper. The glass targets have a high laser damage threshold and are coated via physical vapor deposition with μm thick films. In addition, nm-thin layers of Ti are used as an interface layer for improved ablation efficiency and reduced coating stress. Hence, the metallic or ceramic coating has a lateral homogeneity within 2% and contaminants less than 5%, being optimal for laser ablation processing. With this method, a short (few ms) and well defined pulse of impurities with about 1017 particles can be injected close to the last closed flux surface of Wendelstein 7-X. In particular, a significant amount of atoms with a velocity of about 1 km/s enters the plasma within 1 ms. The atoms are followed by a negligible concentration of slower clusters and macro-particles. This qualifies the use of the targets and applied laser settings for impurity transport studies with the laser blow-off system in Wendelstein 7-X. © 2020 Author(s).