Anomalous impurity diffusion in models of tokamak edge plasma turbulence

Krlín, L.; Pánek, R.; Pavlo, P.; Petržı́lka, V.; Ştöckel, J.; Svoboda, V.; Kühn, S.; Tskhakaya, D.; Тендлер, М.

doi:10.1007/bf03166395

Cited by 2 publications

(2 citation statements)

References 11 publications

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“…A similar behavior was observed in numerical simulations of tokamak systems (Ref. 28 and references therein). Only when time intervals with uncharged dust are longer than about ten gyration times, the free flights become long enough to provide superdiffusion.…”

Section: Resultssupporting

confidence: 84%

A gedankenexperiment for anomalous diffusion in a charge-fluctuating dusty plasma

Kopp¹,

Shchekinov²

2014

Physics of Plasmas

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Brownian motion with Gaussian-distributed step-sizes is the prototype of diffusive processes with the typical scaling of the mean-square displacement linear with time. There are, however, processes scaling slower or faster in time due to differently (e.g., power-law) distributed step-sizes, commonly referred to as sub-and superdiffusion, respectively. We address the question whether there is actually a physical reason for a discrimination between normal and anomalous diffusion or whether such processes can be regarded as a special case of normal diffusion with a complicated space-and time-dependent diffusion coefficient. In order to get to the bottom of this question, we construct a numerical gedankenexperiment, which is designed to be as simple as possible and consists of dust particles embedded as test particles into a homogeneous magnetic field that randomly changes their charge. The only parameter governing the system is the ratio of the time-scales for gyration and for recharging. By performing full-orbit simulations of such particles, we are for the first time able to (i) describe a system exhibiting sub-, normal, or superdiffusion as an asymptotic behavior, i.e., not merely as an intermediate state during the evolution of the system. We (ii) observe superdiffusion for low values of the controlling parameter, normal diffusion over a wide plateau of intermediate values, and subdiffusion for high values, i.e., we found (iii) a simple system with one single and illustrative parameter controlling whether the system exhibits super-, normal, or subdiffusion. The crucial point is (iv) a competition between ballistic (particles uncharged, extreme superdiffusion) and confined (charged, extreme subdiffusion) motions. Our system is homogeneous in space and time, so that its (v) behavior cannot be described by normal diffusion with a special diffusion coefficient, and the competition is (vi) fundamentally different from a Gaussian random walk and may be regarded as one possible prototype of anomalous diffusion. We discuss briefly possible implications to space and astrophysical dusty plasma. In particular, we show that in a plasma with polydisperse dust particles, a superposition of the three regimes of the anomalous diffusion can simultaneously come into play. V C 2014 AIP Publishing LLC. [http://dx.

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Section: Resultssupporting

confidence: 84%

A gedankenexperiment for anomalous diffusion in a charge-fluctuating dusty plasma

Kopp¹,

Shchekinov²

2014

Physics of Plasmas

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“…Parameters improvement of the applied detection systems and major advances in computer simulations permit to make comparative studies between complex theoretical models and new experimental data. However, basic questions concerning mechanisms of anomalous transport like the creation and behavior of turbulent structures [3], the role of plasma impurities [4], the influence of plasma-wall interaction on edge plasma parameters [5], and consequently on the particle confinement and tokamak performance [6] still remain open. Current experiments in many devices indicate a possibility to measure turbulent filaments in visible light emission corresponding mainly to density fluctuations at the edge [7].…”

Section: Physical Motivationmentioning

confidence: 99%

Design of multi-range tomographic system for transport studies in tokamak plasmas

Weinzettl

Naydenkova

Šesták

et al. 2010

Nuclear Instruments and Methods in Physics Research Section A:

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The integrated spectroscopic system for visible plasma radiation, soft X-ray, and bolometric measurements has been designed for the COMPASS tokamak. This diagnostic allows tomographic reconstruction at a few microseconds time base and features an improved spatial resolution about one centimeter in the pedestal region, where the highest gradient of plasma pressure drives turbulent structures and their propagation towards the wall. In combination with other developed diagnostics on COMPASS, it represents an ideal tool for a measurement and characterization of these radiating plasma structures which are responsible for an extremely high particle/energy transport across magnetic field. The design of the new integrated multichannel spectroscopic diagnostics is reviewed and corresponding technical challenges are described. Additionally, the methods, which will be used for data processing, are briefly mentioned and target physics is discussed.

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Anomalous impurity diffusion in models of tokamak edge plasma turbulence

Cited by 2 publications

References 11 publications

A gedankenexperiment for anomalous diffusion in a charge-fluctuating dusty plasma

A gedankenexperiment for anomalous diffusion in a charge-fluctuating dusty plasma

Design of multi-range tomographic system for transport studies in tokamak plasmas

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