Showing papers by "Felix Schauer published in 2012"

Plans for the creation and studies of electron-positron plasmas in a stellarator

Abstract: Electron-positron plasmas are unique in their behavior due to the mass symmetry. Strongly magnetized electron-positron, or pair, plasmas are present in a number of astrophysical settings, such as astrophysical jets, but they have not yet been created in the laboratory. Plans for the creation and diagnosis of pair plasmas in a stellarator are presented, based on extrapolation of the results from the Columbia Non-neutral Torus stellarator, as well as recent developments in positron sources. The particular challenges of positronium injection and pair plasma diagnostics are addressed.

Serrated Yielding at Cryogenic Temperatures in Structural Components of Wendelstein 7-X

Abstract: Structural materials like stainless steels are prone to serrated yielding at cryogenic temperatures. The serration effect is the unstable yielding resulting in a zigzag shape of the stress-strain curve observed in displacement-controlled tensile tests. Moreover, a local temperature rise in the plastic zone is observed. In the current paper, the theories explaining the serration effect are briefly discussed. With a coupled thermal-mechanical Finite element (FE) model of a tensile test set-up the influence of the test conditions is demonstrated on the observed shape of the stress-strain curve. The FE model is extended to quantify the temperature rise and significance of the serration effect in critical support structures of the magnet system of W7-X. For W7-X loading rates the temperature rise due to yielding is shown to be moderate and yielding does not localize. As a simple and safe approach, plastic collapse of critical components to be operated at 4 K can be judged with a pure mechanical analysis using yield curves obtained at 77 K. In doing so, the thermal-mechanical interaction may be neglected.