Special Issue "Multiscale Methods in Plasma Physics"

A special issue of Plasma (ISSN 2571-6182).

Deadline for manuscript submissions: closed (15 February 2018).

Special Issue Editors

Prof. Dr. Scott E. Parker
E-Mail Website
Guest Editor
Department of Physics, Campus Box 390, University of Colorado, Boulder, CO 80309, USA
Interests: kinetic theory and simulation of plasmas; direct numerical simulation of tokamak plasma turbulence on large massively parallel computers; implicit multiscale methods; gyrokinetic theory; kinetic closure and hybrid models
Prof. Dr. Seiji Ishiguro
E-Mail Website
Guest Editor
Department of Helical Plasma Research, National Institute for Fusion Science, 322-6 Oroshi-cho, Toki City 509-5292, Japan
Interests: simulation study of coherent structure in plasmas; imaging of fusion plasma; multi-scale plasma simulation; plasma particle simulation studies of micro-scale plasma dynamics

Special Issue Information

Dear Colleagues,

The US–Japan Joint Institute of Fusion Theory Workshop on “Multiscale Methods in Plasma Physics” was held August 22–24, 2017 at the University of Colorado, Boulder, USA.  This workshop focused on implicit methods combined with multiscale techniques for bridging fine and coarse scales in plasma physics. Topics included coupling the microturbulence scale with the transport scale in fusion plasmas, orbit-averaging, subcycling, and multiple time step techniques in particle-in-cell models and equation-free methods. International experts in this emerging field came together for a small discussion-oriented workshop. Select papers from work reported at this workshop are highlighted in this Special Issue.

Prof. Dr. Scott E. Parker
Prof. Dr. Seiji Ishiguro
Guest Editors

Manuscript Submission Information

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Keywords

  • Multi-scale
  • Plasma
  • Simulation
  • Computational
  • Magnetic fusion
  • Space plasma physics
  • Particle-in-cell methods
  • Continuum Vlasov methods
  • Transport modeling

Published Papers (7 papers)

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Research

Article
Development of a Gyrokinetic Particle-in-Cell Code for Whole-Volume Modeling of Stellarators
Plasma 2019, 2(2), 179-200; https://doi.org/10.3390/plasma2020014 - 12 May 2019
Cited by 6 | Viewed by 2050
Abstract
We present initial results in the development of a gyrokinetic particle-in-cell code for the whole-volume modeling of stellarators. This is achieved through two modifications to the X-point Gyrokinetic Code (XGC), originally developed for tokamaks. One is an extension to three-dimensional geometries with an [...] Read more.
We present initial results in the development of a gyrokinetic particle-in-cell code for the whole-volume modeling of stellarators. This is achieved through two modifications to the X-point Gyrokinetic Code (XGC), originally developed for tokamaks. One is an extension to three-dimensional geometries with an interface to Variational Moments Equilibrium Code (VMEC) data. The other is a connection between core and edge regions that have quite different field-line structures. The VMEC equilibrium is smoothly extended to the edge region by using a virtual casing method. Non-axisymmetric triangular meshes in which triangle nodes follow magnetic field lines in the toroidal direction are generated for field calculation using a finite-element method in the entire region of the extended VMEC equilibrium. These schemes are validated by basic benchmark tests relevant to each part of the calculation cycle, that is, particle push, particle-mesh interpolation, and field solver in a magnetic field equilibrium of Large Helical Device including the edge region. The developed code also demonstrates collisionless damping of geodesic acoustic modes and steady states with residual zonal flow in the core region. Full article
(This article belongs to the Special Issue Multiscale Methods in Plasma Physics)
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Article
Implicit Temporal Discretization and Exact Energy Conservation for Particle Methods Applied to the Poisson–Boltzmann Equation
Plasma 2018, 1(2), 242-258; https://doi.org/10.3390/plasma1020021 - 09 Oct 2018
Cited by 2 | Viewed by 1087
Abstract
We report on a new multiscale method approach for the study of systems with wide separation of short-range forces acting on short time scales and long-range forces acting on much slower scales. We consider the case of the Poisson–Boltzmann equation that describes the [...] Read more.
We report on a new multiscale method approach for the study of systems with wide separation of short-range forces acting on short time scales and long-range forces acting on much slower scales. We consider the case of the Poisson–Boltzmann equation that describes the long-range forces using the Boltzmann formula (i.e., we assume the medium to be in quasi local thermal equilibrium). We develop a new approach where fields and particle information (mediated by the equations for their moments) are solved self-consistently. The new approach is implicit and numerically stable, providing exact energy conservation. We test different implementations that all lead to exact energy conservation. The new method requires the solution of a large set of non-linear equations. We consider three solution strategies: Jacobian Free Newton Krylov, an alternative, called field hiding which is based on hiding part of the residual calculation and replacing them with direct solutions and a Direct Newton Schwarz solver that considers a simplified, single, particle-based Jacobian. The field hiding strategy proves to be the most efficient approach. Full article
(This article belongs to the Special Issue Multiscale Methods in Plasma Physics)
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Article
Investigation of a Multiple-Timescale Turbulence-Transport Coupling Method in the Presence of Random Fluctuations
Plasma 2018, 1(1), 126-143; https://doi.org/10.3390/plasma1010012 - 12 Jul 2018
Viewed by 1716
Abstract
One route to improved predictive modeling of magnetically confined fusion reactors is to couple transport solvers with direct numerical simulations (DNS) of turbulence, rather than with surrogate models. An additional challenge presented by coupling directly with DNS is the inherent fluctuations in the [...] Read more.
One route to improved predictive modeling of magnetically confined fusion reactors is to couple transport solvers with direct numerical simulations (DNS) of turbulence, rather than with surrogate models. An additional challenge presented by coupling directly with DNS is the inherent fluctuations in the turbulence, which limit the convergence achievable in the transport solver. In this article, we investigate the performance of one numerical coupling method in the presence of turbulent fluctuations. To test a particular numerical coupling method for the transport solver, we use an autoregressive-moving-average model to generate stochastic fluctuations efficiently with statistical properties resembling those of a gyrokinetic simulation. These fluctuations are then added to a simple, solvable problem, and we examine the behavior of the coupling method. We find that monitoring the residual as a proxy for the error can be misleading. From a pragmatic point of view, this study aids us in the full problem of transport coupled to DNS by predicting the amount of averaging required to reduce the fluctuation error and obtain a specific level of accuracy. Full article
(This article belongs to the Special Issue Multiscale Methods in Plasma Physics)
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Article
Fully Kinetic Simulation of Ion-Temperature-Gradient Instabilities in Tokamaks
Plasma 2018, 1(1), 105-118; https://doi.org/10.3390/plasma1010010 - 31 May 2018
Cited by 2 | Viewed by 2411
Abstract
The feasibility of using full ion kinetics, instead of gyrokinetics, in simulating low-frequency Ion-Temperature-Gradient (ITG) instabilities in tokamaks has recently been demonstrated. The present work extends the full ion kinetics to the nonlinear regime and investigates the nonlinear saturation of a single-n [...] Read more.
The feasibility of using full ion kinetics, instead of gyrokinetics, in simulating low-frequency Ion-Temperature-Gradient (ITG) instabilities in tokamaks has recently been demonstrated. The present work extends the full ion kinetics to the nonlinear regime and investigates the nonlinear saturation of a single-n ITG instability due to the E × B trapping mechanism (n is the toroidal mode number). The saturation amplitude predicted by the E × B trapping theory is found to agree with the saturation level observed in the simulation. In extending to the nonlinear regime, we developed a toroidal Boris full orbit integrator, which proved to be accurate in capturing both the short-time scale cyclotron motion and long time scale drift motion, with good kinetic energy conservation and toroidal angular momentum conservation in tokamak equilibrium magnetic fields. This work also extends the previous work from analytic circular magnetic equilibria to general numerical magnetic equilibria, enabling simulation of realistic equilibria reconstructed from tokamak experiments. Full article
(This article belongs to the Special Issue Multiscale Methods in Plasma Physics)
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Article
Improvement of the Multi-Hierarchy Simulation Model Based on the Real-Space Decomposition Method
Plasma 2018, 1(1), 90-104; https://doi.org/10.3390/plasma1010009 - 27 Apr 2018
Viewed by 1501
Abstract
Multi-hierarchy simulation models aimed at analysis of magnetic reconnection were developed. Based on the real-space decomposition method, the simulation domain consists of three parts: a magnetohydrodynamics (MHD) domain, a particle-in-cell (PIC) domain, and an interface domain to communicate MHD and PIC data. In [...] Read more.
Multi-hierarchy simulation models aimed at analysis of magnetic reconnection were developed. Based on the real-space decomposition method, the simulation domain consists of three parts: a magnetohydrodynamics (MHD) domain, a particle-in-cell (PIC) domain, and an interface domain to communicate MHD and PIC data. In this paper, the previous model (the 1D interlocking with the upstream condition) by the authors is improved to three types of new models, i.e., two types of the 1D interlocking with the downstream condition and one type of the 2D interlocking with the upstream condition. For their verification, simulations of plasma propagation across the multiple domains were performed in the multi-hierarchy models, and it was confirmed that the new interlocking methods are physically correct. Full article
(This article belongs to the Special Issue Multiscale Methods in Plasma Physics)
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Article
The Role of Magnetic Islands in Collisionless Driven Reconnection: A Kinetic Approach to Multi-Scale Phenomena
Plasma 2018, 1(1), 68-77; https://doi.org/10.3390/plasma1010007 - 21 Apr 2018
Cited by 2 | Viewed by 1645
Abstract
The role of magnetic islands in collisionless driven reconnection has been investigated from the standpoint of a kinetic approach to multi-scale phenomena by means of two-dimensional particle-in-cell (PIC) simulation. There are two different types of the solutions in the evolution of the reconnection [...] Read more.
The role of magnetic islands in collisionless driven reconnection has been investigated from the standpoint of a kinetic approach to multi-scale phenomena by means of two-dimensional particle-in-cell (PIC) simulation. There are two different types of the solutions in the evolution of the reconnection system. One is a steady solution in which the system relaxes into a steady state, and no island is generated (the no-island case). The other is an intermittent solution in which the system does not reach a steady state, and magnetic islands are frequently generated in the current sheet (the multi-island case). It is found that the electromagnetic energy is more effectively transferred to the particle energy in the multi-island case compared with the no-island case. The transferred energy is stored inside the magnetic island in the form of the thermal energy through compressional heating, and is carried away together with the magnetic island from the reconnection region. These results suggest that the formation of a magnetic island chain may have a potential to bridge the energy gap between macroscopic and microscopic physics by widening the dissipation region and strengthening the energy dissipation rate. Full article
(This article belongs to the Special Issue Multiscale Methods in Plasma Physics)
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Article
Microscopic Effect on Filamentary Coherent Structure Dynamics in Boundary Layer Plasmas
Plasma 2018, 1(1), 61-67; https://doi.org/10.3390/plasma1010006 - 22 Mar 2018
Cited by 2 | Viewed by 1778
Abstract
This study has demonstrated kinetic behaviors on the plasma filament propagation with the three-dimensional (3D) Particle-in-Cell (PIC) simulation. When the ion-to-electron temperature ratio Ti/Te is higher, the poloidal symmetry breaking in the filament propagation occurs. The poloidal symmetry breaking [...] Read more.
This study has demonstrated kinetic behaviors on the plasma filament propagation with the three-dimensional (3D) Particle-in-Cell (PIC) simulation. When the ion-to-electron temperature ratio T i / T e is higher, the poloidal symmetry breaking in the filament propagation occurs. The poloidal symmetry breaking is thought to be induced by the unbalanced potential structure that arises from the effect of the gyro motion of plasma particles. Full article
(This article belongs to the Special Issue Multiscale Methods in Plasma Physics)
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