Pavlos Xanthopoulos

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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(More)
We consider the following evolution system of Klein-Gordon-Schrödinger type iψt + κψxx + iαψ = φψ, x ∈ Ω, t > 0, φtt − φxx + φ+ λφt = −Reψx, x ∈ Ω, t > 0, satisfying the following initial and boundary conditions ψ(x, 0) = ψ0(x), φ(x, 0) = φ0(x), φt(x, 0) = φ1(x), x ∈ Ω, ψ(x, t) = φ(x, t) = 0, x ∈ ∂Ω, t > 0, with κ, α, λ positive constants and Ω a bounded(More)
Fusion energy research has in the past 40 years focused primarily on the tokamak concept, but recent advances in plasma theory and computational power have led to renewed interest in stellarators. The largest and most sophisticated stellarator in the world, Wendelstein 7-X (W7-X), has just started operation, with the aim to show that the earlier weaknesses(More)
Turbulence is widely expected to limit the confinement and, thus, the overall performance of modern neoclassically optimized stellarators. We employ novel petaflop-scale gyrokinetic simulations to predict the distribution of turbulence fluctuations and the related transport scaling on entire stellarator magnetic surfaces and reveal striking differences to(More)
in toroidal configurations P. Xanthopoulos, W. A. Cooper, F. Jenko, Yu. Turkin, A. Runov, and J. Geiger EURATOM Association, Max-Planck-Institut für Plasmaphysik, Wendelsteinstr. 1, D-17491 Greifswald, Germany Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, Station 13, CH-1015 Lausanne, Switzerland EURATOM(More)
Ion-temperature-gradient turbulence constitutes a possibly dominant transport mechanism for optimized stellarators, in view of the effective suppression of neoclassical losses characterizing these devices. Nonlinear gyrokinetic simulation results for the Wendelstein 7-X stellarator [G. Grieger, in (IAEA, Vienna, 1991) Vol. 3, p. 525]-assuming an adiabatic(More)
The effects of a non-axisymmetric (3D) equilibrium magnetic field on the linear ion-temperaturegradient (ITG) driven mode are investigated. We consider the strongly driven, toroidal branch of the instability in a global (on the magnetic surface) setting. Previous studies have focused on particular features of non-axisymmetric systems, such as strong local(More)
In the complex 3D magnetic fields of stellarators, ion-temperature-gradient turbulence is shown to have two distinct saturation regimes, as revealed by petascale numerical simulations and explained by a simple turbulence theory. The first regime is marked by strong zonal flows and matches previous observations in tokamaks. The newly observed second regime,(More)
Statistical analysis and modeling of intermittent transport events in the tokamak scrape-off layer Johan Anderson, a) Federico D. Halpern, Pavlos Xanthopoulos, Paolo Ricci, and Ivo Furno Department of Earth and Space Sciences, Chalmers University of Technology, SE-412 96 Göteborg, Sweden École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches(More)
System codes are commonly employed for the analysis and conceptual design of fusion reactors. For the helical-axis advanced stellarator (HELIAS) line, a new set of system code models have been developed to account for the stellarator-specific 3-D aspects. The models have recently been implemented in the systems code PROCESS and verified with respect to(More)