R. Schrittwieser

Common physical mechanism for concentric and non-concentric multiple double layers in plasma

Experimental results are presented on the generation and dynamics of concentric as well as non-concentric multiple double layers in hot filament type discharge plasma. These results emphasize striking similarities between the generation and dynamics of both types of multiple double layers, i.e. similar potential steps corresponding to the ionization energy in used gas, similar hysteresis cycles in the current–voltage characteristic of the exciting electrode, similar dynamic behaviour, etc. The results show that a common physical mechanism is at the origin of both phenomena, in which electron-neutral impact excitation and ionization reactions play a key role.

The electrostatic ion-cyclotron instability. A two-dimensional potential relaxation instability

An experimental investigation shows that the electrostatic ion-cyclotron instability, driven by an electron current to a positively biased collector, is accompanied by strong coherent two-dimensional fluctuations of the plasma potential in front of the collector. These results suggest that this instability evolves like a two-dimensional potential relaxation instability.

Ion-acoustic instability in the presence of high frequency oscillations

Measurements are presented of a standing ion-acoustic wave instability, which is excited by a positively biased grid inserted perpendicularly into the plasma column of a single-ended Q-machine, under the influence of a high frequency signal superimposed onto the positive voltage at the grid. The experimental results show that in certain regions of the frequency and amplitude of the h.f. signal the ion wave instability is stabilized or destabilized. A possible explanation of these effects is presented.

Robust Highly Emissive Probe For Plasma Potential Measurements In The Edge Region Of Toroidal Plasmas

B.S. Schneider∗a, S. Costeaa, C. Ionitaa, R. Schrittwiesera, V. Naulinb, J.J. Rasmussenb, R. Stärzac, N. Vianellod , J. Kovacice and T. Gyergyek f aInstitute for Ion Physics and Applied Physics, University of Innsbruck Technikerstr. 25, 6020 Innsbruck, Austria bDTU Physics, Technical University of Denmark Anker Engelunds Vej 1, 2800 Kgs. Lyngby, Denmark cMechatronic Department, Management Center Innsbruck Universitätsstraße 15, 6020 Innsbruck, Austria dCentre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne CH-1015 Lausanne, Switzerland eJozef Stefan Institute Jamova cesta 39, 1000 Ljubljana, Slovenia f Faculty of Electrical Engineering, University of Ljubljana Trzaska 25, 1000 Ljubljana Slovenia E-mail: bernd.s.schneider@uibk.ac.at, stefan.costea@uibk.ac.at, codrina.ionita@uibk.ac.at, roman.schrittwieser@uibk.ac.at, vona@fysik.dtu.dk, jjra@fysik.dtu.dk, Ronald.Staerz@mci.edu, nicola.vianello@epfl.ch, jernej.kovacic@ijs.si, tomaz.gyergyek@ijs.si