| 1. |
- Anderson, Johan, 1973, et al.
(författare)
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A fractional Fokker-Planck model for anomalous diffusion
- 2014
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 21:12, s. aricle no: 122109-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a study of anomalous diffusion using a Fokker-Planck description withfractional velocity derivatives. The distribution functions are found using numerical means forvarying degree of fractionality of the stable Lévy distribution. The statistical properties of thedistribution functions are assessed by a generalized normalized expectation measure and entropyin terms of Tsallis statistical mechanics. We find that the ratio of the generalized entropy andexpectation is increasing with decreasing fractionality towards the well known so-called sub-diffusivedomain, indicating a self-organising behavior.
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| 2. |
- Anderson, Johan, 1973, et al.
(författare)
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Elucidating plasma dynamics in Hasegawa-Wakatani turbulence by information geometry
- 2020
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 27:2
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Tidskriftsartikel (refereegranskat)abstract
- The impact of adiabatic electrons on drift-wave turbulence, modeled by the Hasegawa-Wakatani equations, is studied using information length. Information length is a novel theoretical method for measuring distances between statistical states represented by different probability distribution functions (PDFs) along the path of a system and represents the total number of statistically different states that a system evolves through in time. Specifically, the time-dependent PDFs of turbulent fluctuations for a given adiabatic index A are computed. The changes in fluctuation statistics are then quantified in time by using information length. The numerical results provide time traces exhibiting intermittent plasma dynamics, and such behavior is identified by a rapid change in the information length. The effects of A are discussed.
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| 3. |
- Papadopoulos, Aristeides D., et al.
(författare)
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Statistical Analysis of Plasma Dynamics in Gyrokinetic Simulations of Stellarator Turbulence
- 2023
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Ingår i: Entropy. - 1099-4300. ; 25:6
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Tidskriftsartikel (refereegranskat)abstract
- A geometrical method for assessing stochastic processes in plasma turbulence is investigated in this study. The thermodynamic length methodology allows using a Riemannian metric on the phase space; thus, distances between thermodynamic states can be computed. It constitutes a geometric methodology to understand stochastic processes involved in, e.g., order–disorder transitions, where a sudden increase in distance is expected. We consider gyrokinetic simulations of ion-temperature-gradient (ITG)-mode-driven turbulence in the core region of the stellarator W7-X with realistic quasi-isodynamic topologies. In gyrokinetic plasma turbulence simulations, avalanches, e.g., of heat and particles, are often found, and in this work, a novel method for detection is investigated. This new method combines the singular spectrum analysis algorithm with a hierarchical clustering method such that the time series is decomposed into two parts: useful physical information and noise. The informative component of the time series is used for the calculation of the Hurst exponent, the information length, and the dynamic time. Based on these measures, the physical properties of the time series are revealed.
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