Plunk G.G.,Max Planck Institute for Plasma Physics (Greifswald)
Physics of Plasmas | Year: 2013
To address the problem of Landau damping in kinetic turbulence, we consider the forcing of the linearized Vlasov equation by a stationary random source. It is found that the time-asymptotic density response is dominated by resonant particle interactions that are synchronized with the source. The energy consumption of this response is calculated, implying an effective damping rate, which is the main result of this paper. Evaluating several cases, it is found that the effective damping rate can differ from the Landau damping rate in magnitude and also, remarkably, in sign. A limit is demonstrated in which the density and current become phase-locked, which causes the effective damping to be negligible; this result offers a fresh perspective from which to reconsider recent observations of kinetic turbulence satisfying critical balance. © 2013 American Institute of Physics.
Warmbier R.,Max Planck Institute for Plasma Physics (Greifswald) |
Schneider R.,University of Greifswald
Physical Chemistry Chemical Physics | Year: 2011
This work presents a new ground state potential energy surface (PES) for CH+2. The potential is tested using quasi classical trajectory (QCT) and quantum reactive scattering methods for the H + CH+ reaction. Cross sections and rate coefficients for all reaction channels up to 300 K are calculated. The abstraction rate coefficients follow the expected slightly decreasing behaviour above 90 K, but have a positive gradient with lower temperatures. The inelastic collision and exchange reaction rate constants are increasing monotonically with temperature. The rate coefficients of the exchange reaction differ significantly between QCT and quantum reactive scattering, due to intrinsic shortcomings of the QCT final state distributions. © 2011 the Owner Societies.
Hirsch M.,Max Planck Institute for Plasma Physics (Greifswald)
Contributions to Plasma Physics | Year: 2010
The observation of the H-mode and ELMs in helical devices confirms the generic character of these phenomena in toroidal confinement. Particularities are the strong impact of the magnetic edge configuration on transition and ELM phenomenology and the existence of a mean E × B flow shear already predefined by the condition given from the neoclassical fluxes. The observations indicate that the classical H-mode as a bifurcation phenomenon possibly associated with dynamic sheared flows is biased by these equilibrium mean shear flow conditions of the 3D plasma edge. Besides this classical H-mode other Edge Transport Barriers can be realized which are related to the development a mean shear flow on a transport timescale. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Helander P.,Max Planck Institute for Plasma Physics (Greifswald)
Physical Review Letters | Year: 2014
It is shown that magnetically confined electron-positron plasmas can enjoy remarkable stability properties. Many of the microinstabilities driving turbulence and transport in electron-ion plasmas are absent if the density is so low that the Debye length is significantly larger than the gyroradius. In some magnetic configurations, almost complete linear stability may be attainable in large parts of the parameter space. © 2014 American Physical Society.
Mynick H.E.,Princeton Plasma Physics Laboratory |
Pomphrey N.,Princeton Plasma Physics Laboratory |
Xanthopoulos P.,Max Planck Institute for Plasma Physics (Greifswald)
Physical Review Letters | Year: 2010
Up to now, the term "transport-optimized" stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely, gyrokinetic codes valid for 3D nonlinear simulations and stellarator optimization codes. Two initial proof-of-principle configurations are obtained, reducing the level of ion temperature gradient turbulent transport from the National Compact Stellarator Experiment baseline design by a factor of 2-2.5. © 2010 The American Physical Society.