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Plasma
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Magnetic Confinement Fusion
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Magnetic Confinement Fusion

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

Deadline for manuscript submissions: closed (15 March 2019) | Viewed by 18576

Special Issue Editor

Dr. Eun-jin Kim

E-Mail Website
Guest Editor
School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH, UK
Interests: fluid dynamics; magnetohydrodynamics (MHD); plasma physics; self-organisation; non-equilibrium statistical mechanics; turbulence; solar/stellar physics; magnetic fusion; information theory; homeostasis in biosystems
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Magnetic fusion utilises nuclear energy released when lighter atoms combine to form heavier ones in hot, ionised gas (plasmas). While it has been a power engine of the universe, its commercialisation for power plants for carbon free-energy has been hampered by the lack of control of laboratory plasmas, which are extremely volatile, with temperatures of several million degrees Celsius (hotter than the centre of the Sun). Excited on a broad range of scales, numerous instabilities cause anomalous transport, significantly degrading the confinement. Understanding and controlling anomalous transport is a key challenge to the success of fusion reactors (e.g., International Thermonuclear Experimental Reactor). Fusion plasmas, in fact, constitute an example of non-equilibrium systems where multiple scales are excited and interact with each other in a complex way, a proper description of which has always been a major challenge in many disciplines.

This Special Issue aims to present different approaches to this challenging problem in fusion plasmas. Submissions reporting recent developments in theory, numerical simulations and experiments are especially welcome.

Prof. Dr. Eun-jin Kim
Guest Editor

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Keywords

  • Magnetic fusion
  • Plasma physics
  • Tokamak
  • ITER
  • Multiscale modelling
  • Plasmas transport
  • Plasma turbulence
  • Anomalous transport
  • Transport barrier
  • Plasma confinement
  • Plasma bifurcation
  • Gyro-kinetic theory
  • L-H transition
  • Plasma simulations

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Published Papers (4 papers)

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Research

11 pages, 2856 KiB  
Article
H-Mode Power Threshold Studies on MAST
by Yasmin Andrew, Jan-Peter Bähner, Ronan Battle and Tomas Jirman
Plasma 2019, 2(3), 328-338; https://doi.org/10.3390/plasma2030024 - 19 Jul 2019
Cited by 9 | Viewed by 5791
Abstract
Analysis of the L–H and H–L transition power thresholds (Pth) and pedestal parameters are presented for the mega ampere spherical tokamak (MAST). The dependencies of Pth on the average, core plasma electron density, X-point height, and plasma current are [...] Read more.
Analysis of the L–H and H–L transition power thresholds (Pth) and pedestal parameters are presented for the mega ampere spherical tokamak (MAST). The dependencies of Pth on the average, core plasma electron density, X-point height, and plasma current are described. Increasing X-point distance from the divertor floor over 10–12 cm is found to increase Pth by a factor of three, while X-point heights greater than this have no further influence. The X-point height dependence of Pth is also observed to be sensitive to the plasma current. An Ip decrease from 0.77 MA to 0.65 MA, is observed to lower Pth by a factor of three across the X-point height scan and increases the maximum X-point height at which Pth stops increasing by 3 cm. Finally, a comparison of the experimental results with the predictions by the finite beta drift wave model is made, which provides a reasonable condition for the transition into and out of the H-mode. Full article
(This article belongs to the Special Issue Magnetic Confinement Fusion)
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29 pages, 4220 KiB  
Article
Transport Barrier Triggered by Resonant Three-Wave Processes Between Trapped-Particle-Modes and Zonal Flow
by Alain Ghizzo and Daniele Del Sarto
Plasma 2019, 2(2), 229-257; https://doi.org/10.3390/plasma2020017 - 2 Jun 2019
Cited by 3 | Viewed by 4048
Abstract
We address the mechanisms underlying low-frequency zonal flow generation in a turbulent system through the parametric decay of collisionless trapped particle modes and its feedback on the stabilization of the system. This model is in connection with the observation of barrier transport in [...] Read more.
We address the mechanisms underlying low-frequency zonal flow generation in a turbulent system through the parametric decay of collisionless trapped particle modes and its feedback on the stabilization of the system. This model is in connection with the observation of barrier transport in reduced gyrokinetic simulations (A. Ghizzo et al., Euro. Phys. Lett. 119(1), 15003 (2017)). Here the analysis is extended with a detailed description of the resonant mechanism. A key role is also played by an initial polarisation source that allows the emergence of strong initial shear flow. The parametric decay leads to the growth of a zonal flow which differs from the standard zero frequency zonal flow usually triggered by the Reynolds stress in fluid drift-wave turbulence. The resulting zonal flow can oscillate at low frequency close to the ion precession frequency, making it sensitive to strong amplification by resonant kinetic processes. The system becomes then intermittent. These new findings, obtained from numerical experiments based on reduced semi-Lagrangian gyrokinetic simulations, shed light on the underlying physics coming from resonant wave-particle interactions for the formation of transport barriers. Numerical simulations are based on a Hamiltonian reduction technique, including magnetic curvature and interchange turbulence, where both fastest scales (cyclotron and bounce motions) are gyro-averaged. Full article
(This article belongs to the Special Issue Magnetic Confinement Fusion)
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11 pages, 1143 KiB  
Article
Amplitude Modulation And Nonlinear Self-Interactions of the Geodesic Acoustic Mode at the Edge of MAST
by Bogdan Hnat, Nicholas Walkden and The MAST Team
Plasma 2019, 2(2), 168-178; https://doi.org/10.3390/plasma2020013 - 8 May 2019
Cited by 1 | Viewed by 3301
Abstract
We studied the amplitude modulation of the radial electric field constructed from the Langmuir probe plasma potential measurements at the edge of the mega-ampere spherical tokamak (MAST). The Empirical Mode Decomposition (EMD) technique was applied, which allowed us to extract fluctuations on temporal [...] Read more.
We studied the amplitude modulation of the radial electric field constructed from the Langmuir probe plasma potential measurements at the edge of the mega-ampere spherical tokamak (MAST). The Empirical Mode Decomposition (EMD) technique was applied, which allowed us to extract fluctuations on temporal scales of plasma turbulence, the Geodesic Acoustic Mode (GAM), and those associated with the residual poloidal flows. This decomposition preserved the nonlinear character of the signal. Hilbert transform (HT) was then used to obtain the amplitude modulation envelope of fluctuations associated with turbulence and with the GAM. We found significant spectral coherence at frequencies between 1–5 kHz, in the turbulence and the GAM envelopes and for the signal representing the low frequency zonal flows (LFZFs). We present the evidence of local and nonlocal, in frequency space, three wave interactions leading to coupling between the GAM and the low frequency (LF) part of the spectrum. Full article
(This article belongs to the Special Issue Magnetic Confinement Fusion)
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36 pages, 1726 KiB  
Article
Computing the Double-Gyroaverage Term Incorporating Short-Scale Perturbation and Steep Equilibrium Profile by the Interpolation Algorithm
by Shuangxi Zhang, Michel Mehrenberger and Christophe Steiner
Plasma 2019, 2(2), 91-126; https://doi.org/10.3390/plasma2020009 - 9 Apr 2019
Viewed by 4431
Abstract
In the gyrokinetic model and simulations, when the double-gyroaverage term incorporates the combining effect contributed by the finite Larmor radius, short scales of the perturbation, and steep gradient of the equilibrium profile, the low-order approximation of this term could generate unignorable error. This [...] Read more.
In the gyrokinetic model and simulations, when the double-gyroaverage term incorporates the combining effect contributed by the finite Larmor radius, short scales of the perturbation, and steep gradient of the equilibrium profile, the low-order approximation of this term could generate unignorable error. This paper implements an interpolation algorithm to compute the double-gyroaverage term without low-order approximation to avoid this error. For a steep equilibrium density, the obvious difference between the density on the gyrocenter coordinate frame and the one on the particle coordinate frame should be accounted for in the quasi-neutrality equation. A Euler–Maclaurin-based quadrature integrating algorithm is developed to compute the quadrature integral for the distribution of the magnetic moment. The application of the interpolation algorithm to computing the double-gyroaverage term and to solving the quasi-neutrality equation is benchmarked by comparing the numerical results with the known analytical solutions. Finally, to take advantage of the interpolation solver clearer, the numerical comparison between the interpolation solver and a classical second order solver is carried out in a constant theta-pinch magnetic field configuration using SELALIB code. When the equilibrium profile is not steep and the perturbation only has the non-zero mode number along the parallel spatial dimension, the results computed by the two solvers match each other well. When the gradient of the equilibrium profile is steep, the interpolation solver provides a bigger driving effect for the ion-temperature-gradient modes, which possess large polar mode numbers. Full article
(This article belongs to the Special Issue Magnetic Confinement Fusion)
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