O. Grulke

Publications (92) View all

• Article: Measurements of HF-Plasma Oscillations by means of a Laser-Heated Emissive Probe

  R Schrittwieser, C Ionita, K Rahbarnia, J Gruenwald, T Windisch, R Staerz, O Grulke, T Klinger
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  ABSTRACT: Indirectly heated emissive probes have advantages compared to conventional emissive wire probes. We have developed a laser-heated emissive probe consisting of a 1 mm diameter and 2 mm long pin of LaB6, heated by a focussed laser beam of 808 nm wavelength with a power up to 50 W. This probe is smaller and simpler than electrically heated emissive wire probes. Materials of low work function, high temperature stability and longer lifetime such as LaB6 can be used. There is no deformation in a magnetic field and no voltage drop along the probe wire. In this contribution we show the good time resolution of such a probe. Whereas emissive wire probes need two cables and an electric power supply or battery, for our probe one connection to an oscilloscope with high input impedance suffices. Therefore the probe system has a much lower stray capacitance than conventional emissive wire probes.
  Contributions to Plasma Physics 01/2013; 53(1, SI):92-95. · 1.11 Impact Factor
• Article: Characterization of neutral loop discharges in the VINETA device

  A Stechow, O Grulke, T Klinger
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  ABSTRACT: A neutral loop (NL) discharge has been implemented in the linear plasma device VINETA with three different antenna configurations. Radial profile measurements of the electron density, temperature and floating potential are performed at various neutral loop radii and compared to single particle simulations. Local density maxima are observed near the NL, for which several mechanisms have been proposed. The measured temperature profiles do not support the model of a thermal heating process, whereas the floating potential profiles corroborate the assumption of a locally enhanced induction current.
  The European Physical Journal D 03/2012; 66(3). · 1.48 Impact Factor
• Article: The influence of magnetic-field gradients and boundaries on double-layer formation in capacitively coupled plasmas

  T Schroeder, O Grulke, T Klinger
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  ABSTRACT: The axial position of a magnetic-field gradient has been varied for capacitive discharges in the linear plasma device VINETA. For low magnetic fields (B <= O(10 mT)), double layers have been observed to form predominantly at the interface between the source and the plasma chamber. In particular, the double-layer position is independent of the position of the magnetic-field gradient. However, shifting the axial location of the magnetic-field gradient leads to a global change of the plasma potential and the strength of the double layer. For higher magnetic fields the position of the double layer can be disentangled from the position of both the diameter interchange and the magnetic-field gradient. Copyright (C) EPLA, 2012
  EPL (Europhysics Letters) 03/2012; 97(6). · 2.17 Impact Factor
• Article: Formation of turbulent structures and the link to fluctuation driven sheared flows

  T Windisch, O Grulke, V Naulin, T Klinger
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  ABSTRACT: The formation of turbulent structures in weakly developed drift-wave turbulence is investigated using experimental data obtained in a linear laboratory device. The findings are compared with fully non-linear numerical simulation results. The formation of structures occurs in a region, in which the divergence of the Reynolds stress, which is one term in the momentum balance, has a maximum. The generation of a time-averaged shear layer is not observed, but for transient events the shearing rate can become sufficiently strong to decorrelate the fluctuations. This happens when the energy flow into the shear flow is largely positive.
  Plasma Physics and Controlled Fusion 12/2011; 53(12, Part 1-2). · 2.42 Impact Factor
• Article: Intermittent transport events in a cylindrical plasma device: experiment and simulation

  T Windisch, O Grulke, V Naulin, T Klinger
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  ABSTRACT: The origin of intermittent fluctuations in the plasma edge of a linearly magnetized plasma column is investigated and closely compared with three-dimensional global numerical simulations. The intermittent character is caused by radially propagating turbulent structures. The radial propagation of the structures is due to the self-consistent potential perturbation associated with them. Their formation is closely linked to transport events caused by nonlinear drift-wave fluctuations. In the formation region a sheared azimuthal flow velocity is observed, which is driven by the Reynolds stress.
  Plasma Physics and Controlled Fusion 08/2011; 53(8). · 2.42 Impact Factor