Stuttgart, Germany
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Stollenwerk L.,Institute For Plasmaforschung | Stollenwerk L.,Institute For Physik | Stroth U.,Institute For Plasmaforschung
Contributions to Plasma Physics | Year: 2011

A dielectric barrier discharge with different electrode surfaces is investigated and the dynamic evolution of surface charge on the dielectric surface is measured optically. It is found that the amount of surface charge after the positive and the negative half-cycle are not equal, i.e. a bias charge emerges. To understand this phenomenon, the transfered charge per half-cycle is estimated from the Paschen curve and the shape of the driving voltage waveform. It turns out that the charge bias is necessary to compensate for the asymmetry of the discharge conditions due to the different surfaces and hence is required for a balanced charge transfer in the steady state. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Strauss D.,Karlsruhe Institute of Technology | Aiello G.,Karlsruhe Institute of Technology | Bruschi A.,EURATOM | Chavan R.,Ecole Polytechnique Federale de Lausanne | And 27 more authors.
Fusion Engineering and Design | Year: 2014

The design of the ITER ECRH system provides 20 MW millimeter wave power for central plasma heating and MHD stabilization. The system consists of an array of 24 gyrotrons with power supplies coupled to a set of transmission lines guiding the beams to the four upper and the equatorial launcher. The front steering upper launcher design described herein has passed successfully the preliminary design review, and it is presently in the final design stage. The launcher consists of a millimeter wave system and steering mechanism with neutron shielding integrated into an upper port plug with the plasma facing blanket shield module (in-vessel) and a set of ex-vessel waveguides connecting the launcher to the transmission lines. Part of the transmission lines are the ultra-low loss CVD torus diamond windows and a shutter valve, a miter bend section and the feedthroughs integrated in the plug closure plate. These components are connected by corrugated waveguides and form together the first confinement system (FCS). In-vessel, the millimeter-wave system includes a quasi-optical beam propagation system including four mirror sets and a front steering mirror. The millimeter wave system is integrated into a specifically optimized upper port plug providing structural stability to withstand plasma disruption forces and the high heat load from the plasma side with a dedicated blanket shield module. A recent update in the ITER interface definition has resulted in the recession of the upper port plug first wall panels, which is now integrated into the design. Apart from the millimeter wave system the upper port plug houses also a set of shield blocks which provide neutron shielding. An overview of the actual ITER ECRH Upper Launcher is given together with some highlights of the design. © 2014 Elsevier B.V.

Pfannmoller J.P.,Max Planck Institute for Plasma Physics (Greifswald) | Lechte C.,Institute For Plasmaforschung | Grulke O.,Max Planck Institute for Plasma Physics (Greifswald) | Grulke O.,University of Greifswald | And 2 more authors.
Physics of Plasmas | Year: 2012

Experimental investigations and simulations of loop antenna excited whistler waves in a cylindrical low temperature plasma are presented. Experiments are performed in the VINETA [Franck, Plasma Sources Sci. Technol. 14, 226 (2005)] device and simulations are generated using IPF-FD3D [C. Lechte, IEEE Trans. Plasma Sci. 37, 1099 (2009)], an implementation of the Yee-algorithm. A good agreement of the experiment and the simulation is found. The simulation is used to predict the spatial structure of the wave, the dominant source of the electric field, the relative contribution of electron, and displacement current as well as parallel and perpendicular currents to the magnetic field of the wave. © 2012 American Institute of Physics.

Strauss D.,Karlsruhe Institute of Technology | Aiello G.,Karlsruhe Institute of Technology | Chavan R.,Ecole Polytechnique Federale de Lausanne | Cirant S.,EURATOM | And 25 more authors.
Fusion Engineering and Design | Year: 2013

The design of the ITER electron cyclotron launchers recently reached the preliminary design level - the last major milestone before design finalization. The ITER ECH system contains 24 installed gyrotrons providing a maximum ECH injected power of 20 MW through transmission lines towards the tokamak. There are two EC launcher types both using a front steering mirror; one equatorial launcher (EL) for plasma heating and four upper launchers (UL) for plasma mode stabilization (neoclassical tearing modes and the sawtooth instability). A wide steering angle range of the ULs allows focusing of the beam on magnetic islands which are expected on the rational magnetic flux surfaces q = 1 (sawtooth instability), q = 3/2 and q = 2 (NTMs). In this paper the preliminary design of the ITER ECH UL is presented, including the optical system and the structural components. Highlights of the design include the torus CVD-diamond windows, the frictionless, front steering mechanism and the plasma facing blanket shield module (BSM). Numerical simulations as well as prototype tests are used to verify the design © 2013 Elsevier B.V.

Fuchert G.,Institute For Plasmaforschung | Boettcher T.,Institute For Plasmaforschung | Ramisch M.,Institute For Plasmaforschung | Stroth U.,Institute For Plasmaforschung
38th EPS Conference on Plasma Physics 2011, EPS 2011 - Europhysics Conference Abstracts | Year: 2011

Mesoscale (i. e. larger than microscopic but smaller than the system size) turbulent fluctu-ations of high density, often referred to as "blobs", may be a part of the explanation of the intermittent transport observed in the scrape-off layer (SOL) of many fusion experiments. The understanding of those mesoscale events has improved a lot over the recent years [1]. However, the details about the generation and the precise relevance for the SOL transport remain still unknown. Fast cameras are gaining more and more importance in studies of those events, since they can observe a large area of the plasma simultaneously, ideally without the need to disturb the plasma. However, the fact that they integrate the light signal along the line of sight makes the interpretation of the data more challenging. Yet it was possible to localize the turbulent fluctuations visible in the image data in the physical coordinates of TJ-K.

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