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Anomalous diffusion of plasma in tokamak edge region
Seidl, Jakub ; Krlín, Ladislav (advisor) ; Hrach, Rudolf (referee) ; Rohlena, Karel (referee)
Title: Anomalous diffusion of plasma in tokamak edge region Author: Jakub Seidl Tutoring institution: Institute of Plasma Physics AS CR, v.v.i. Supervisor: Doc. Ing. Ladislav Krlín, DrSc., IPP AS CR Consultant: RNDr. Radomír Pánek, Ph.D., IPP AS CR Abstract: This work provides brief introduction to the topic of plasma turbu- lence in tokamak edge region and several aspects of anomalous plasma diffusion are discussed. We use numerical code ESEL to model interchange turbulence and investigate properties of turbulent structures in different regimes of parallel trans- port. Means of experimental verification of the results are discussed. Results of the modelling are then used to interpret unexpected results experimentally obtained by electrostatic ball-pen probes on tokamak ASDEX Upgrade, mainly appearance of a 'bump' in power spectra of measured plasma potential. Next, we explain be- haviour of cross-correlation function of density signals measured by two spatially separated Langmuir probes in the vicinity of magnetic separatrix and we point out an ambiguity in interpretation of results of vorticity measurement made by set of floating Langmuir probes. In the last part, transport of plasma impurities by electrostatic turbulent potential is modelled. We identify reversal of radial particle velocity for particles with...
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Anomalous diffusion of plasma in tokamak edge region
Seidl, Jakub ; Krlín, Ladislav (advisor) ; Hrach, Rudolf (referee) ; Rohlena, Karel (referee)
Title: Anomalous diffusion of plasma in tokamak edge region Author: Jakub Seidl Tutoring institution: Institute of Plasma Physics AS CR, v.v.i. Supervisor: Doc. Ing. Ladislav Krlín, DrSc., IPP AS CR Consultant: RNDr. Radomír Pánek, Ph.D., IPP AS CR Abstract: This work provides brief introduction to the topic of plasma turbu- lence in tokamak edge region and several aspects of anomalous plasma diffusion are discussed. We use numerical code ESEL to model interchange turbulence and investigate properties of turbulent structures in different regimes of parallel trans- port. Means of experimental verification of the results are discussed. Results of the modelling are then used to interpret unexpected results experimentally obtained by electrostatic ball-pen probes on tokamak ASDEX Upgrade, mainly appearance of a 'bump' in power spectra of measured plasma potential. Next, we explain be- haviour of cross-correlation function of density signals measured by two spatially separated Langmuir probes in the vicinity of magnetic separatrix and we point out an ambiguity in interpretation of results of vorticity measurement made by set of floating Langmuir probes. In the last part, transport of plasma impurities by electrostatic turbulent potential is modelled. We identify reversal of radial particle velocity for particles with...
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Impurity Dynamics in Turbulent Plasma in Tokamak Scrape-off Layer
Seidl, J. ; Krlín, Ladislav
We simulate behavior of plasma impurities in turbulent potential in tokamak scrape-off layer. Assuming low density of impurities we use test particle approach to investigate movement of individual particles in time evolving potential of isolated structure generated by interchange instability. Behavior of the plasma is modeled using reduced fluid model. We compare behavior of test particles under guiding center drift approximation with full-orbit 2D Hamiltonian equations of motion. While we find flow of particles governed purely by ExB drift to be incompressible, including also polarization drift results in compressibility of the flow. Particles traced along their full orbits exhibit the compressibility as well, however, larger in space and different in its amplitude. We therefore conclude that neglecting finite Larmor radius and assuming dynamics based on drift approximation may introduce significant error into simulations of impurity behavior in tokamak SOL.
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Bellanova nestabilita u nečistot zachycených v turbulentních strukturách v okrajové vrstvě tokamaku
Seidl, J. ; Krlín, Ladislav
We present description of an electrostatic turbulent model ESEL and explain interchange mechanism leading to turbulence generation in tokamak scrape-off layer. After introducing theory of Bellan instability, threshold for particle detrapping from turbulent structures (blobs) due to their finite Larmor orbits is discussed for the case of turbulence simulated by the ESEL model. Since plasma potential as well as floating potential are available from the simulation, it is possible to evaluate error made by using experimentally obtained floating potential in simulations of particle diffusion. It is shown that due to bipolar nature of blobs the outflow of particles from the blob caused by Bellan instability can be, in certain conditions, asymmetric and localized mainly into its upper and inner boundary.
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