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Plunk GG, Xanthopoulos P, Weir GM, Bozhenkov SA, Dinklage A, Fuchert G, Geiger J, Hirsch M, Hoefel U, Jakubowski M, Langenberg A, Pablant N, Pasch E, Stange T, Zhang D, W-X Team T. Stellarators Resist Turbulent Transport on the Electron Larmor Scale. PHYSICAL REVIEW LETTERS 2019; 122:035002. [PMID: 30735428 DOI: 10.1103/physrevlett.122.035002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 11/07/2018] [Indexed: 06/09/2023]
Abstract
Electron temperature gradient (ETG)-driven turbulence, despite its ultrafine scale, is thought to drive significant thermal losses in magnetic fusion devices-but what role does it play in stellarators? The first numerical simulations of ETG turbulence for the Wendelstein 7-X stellarator, together with power balance analysis from its initial experimental operation phase, suggest that the associated transport should be negligible compared to other channels. The effect, we argue, originates essentially from the geometric constraint of multiple field periods, a generic feature of stellarators.
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Affiliation(s)
- G G Plunk
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - P Xanthopoulos
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - G M Weir
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - S A Bozhenkov
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - A Dinklage
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - G Fuchert
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - J Geiger
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - M Hirsch
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - U Hoefel
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - M Jakubowski
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - A Langenberg
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - N Pablant
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - E Pasch
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - T Stange
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - D Zhang
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - The W-X Team
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
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Jorge R, Ricci P, Loureiro NF. Theory of the Drift-Wave Instability at Arbitrary Collisionality. PHYSICAL REVIEW LETTERS 2018; 121:165001. [PMID: 30387626 DOI: 10.1103/physrevlett.121.165001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Revised: 09/07/2018] [Indexed: 06/08/2023]
Abstract
A numerically efficient framework that takes into account the effect of the Coulomb collision operator at arbitrary collisionalities is introduced. Such a model is based on the expansion of the distribution function on a Hermite-Laguerre polynomial basis to study the effects of collisions on magnetized plasma instabilities at arbitrary mean-free path. Focusing on the drift-wave instability, we show that our framework allows retrieving established collisional and collisionless limits. At the intermediate collisionalities relevant for present and future magnetic nuclear fusion devices, deviations with respect to collision operators used in state-of-the-art turbulence simulation codes show the need for retaining the full Coulomb operator in order to obtain both the correct instability growth rate and eigenmode spectrum, which, for example, may significantly impact quantitative predictions of transport. The exponential convergence of the spectral representation that we propose makes the representation of the velocity space dependence, including the full collision operator, more efficient than standard finite difference methods.
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Affiliation(s)
- R Jorge
- École Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland
- Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
| | - P Ricci
- École Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland
| | - N F Loureiro
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Whelan GG, Pueschel MJ, Terry PW. Nonlinear Electromagnetic Stabilization of Plasma Microturbulence. PHYSICAL REVIEW LETTERS 2018; 120:175002. [PMID: 29756837 DOI: 10.1103/physrevlett.120.175002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Revised: 02/26/2018] [Indexed: 06/08/2023]
Abstract
The physical causes for the strong stabilizing effect of finite plasma β on ion-temperature-gradient-driven turbulence, which far exceeds quasilinear estimates, are identified from nonlinear gyrokinetic simulations. The primary contribution stems from a resonance of frequencies in the dominant nonlinear interaction between the unstable mode, the stable mode, and zonal flows, which maximizes the triplet correlation time and therefore the energy transfer efficiency. A modification to mixing-length transport estimates is constructed, which reproduces nonlinear heat fluxes throughout the examined β range.
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Affiliation(s)
- G G Whelan
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - M J Pueschel
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
- Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712, USA
| | - P W Terry
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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Howes GG. A prospectus on kinetic heliophysics. PHYSICS OF PLASMAS 2017; 24:055907. [PMID: 29104421 PMCID: PMC5648573 DOI: 10.1063/1.4983993] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2017] [Accepted: 05/01/2017] [Indexed: 05/29/2023]
Abstract
Under the low density and high temperature conditions typical of heliospheric plasmas, the macroscopic evolution of the heliosphere is strongly affected by the kinetic plasma physics governing fundamental microphysical mechanisms. Kinetic turbulence, collisionless magnetic reconnection, particle acceleration, and kinetic instabilities are four poorly understood, grand-challenge problems that lie at the new frontier of kinetic heliophysics. The increasing availability of high cadence and high phase-space resolution measurements of particle velocity distributions by current and upcoming spacecraft missions and of massively parallel nonlinear kinetic simulations of weakly collisional heliospheric plasmas provides the opportunity to transform our understanding of these kinetic mechanisms through the full utilization of the information contained in the particle velocity distributions. Several major considerations for future investigations of kinetic heliophysics are examined. Turbulent dissipation followed by particle heating is highlighted as an inherently two-step process in weakly collisional plasmas, distinct from the more familiar case in fluid theory. Concerted efforts must be made to tackle the big-data challenge of visualizing the high-dimensional (3D-3V) phase space of kinetic plasma theory through physics-based reductions. Furthermore, the development of innovative analysis methods that utilize full velocity-space measurements, such as the field-particle correlation technique, will enable us to gain deeper insight into these four grand-challenge problems of kinetic heliophysics. A systems approach to tackle the multi-scale problem of heliophysics through a rigorous connection between the kinetic physics at microscales and the self-consistent evolution of the heliosphere at macroscales will propel the field of kinetic heliophysics into the future.
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Affiliation(s)
- Gregory G Howes
- Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
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