Stochastic (E×B) diffusion of ions in a spatially periodical potential field

Krlín, L.; Ştöckel, J.; Svoboda, V.

doi:10.1088/0741-3335/41/3/002

Cited by 10 publications

(13 citation statements)

References 13 publications

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“…Considering a particle travelling on the hill, there appear, namely, two regimes of its motion. According to paper of Bellan [11] and of our paper [1], there appears an instability for the case with R ≥ 0.25. A particle with this parameter spirals downhill until it enters the separatrix region.…”

Section: Introductionmentioning

confidence: 68%

“…To understand more properly to the effect of anomalous diffusion of ions, found in the regime of edge tokamak plasma turbulence, we have recently [1,2] started with very simple model of the turbulent potential. Instead of obviously time and spatially uncorrelated dependencies, we use the spatially periodical model shown in Figs.…”

Section: Introductionmentioning

confidence: 99%

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confidence: 97%

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Anomalous impurity diffusion in models of tokamak edge plasma turbulence

et al. 2004

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Using a simple spatially periodical and stationary potential as a model of electrostatic tokamak edge plasma turbulence, we have found recently [1,2] an anomalous impurity diffusion in this regime. In this contribution, we estimate this diffusion for a more general and realistic form of the potential, which is close to the Hasegawa-Wakatani (HW) potential. As an interesting consequence of the discussed dynamics, we present possibility of radial electric field generation in the edge turbulence regime. This effect might play a role in tokamak scenarios with transport barriers.PACS : 52.25.Fi

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Section: Introductionmentioning

confidence: 68%

Section: Introductionmentioning

confidence: 99%

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Anomalous impurity diffusion in models of tokamak edge plasma turbulence

et al. 2004

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“…Some examples of this kind of studies are [2][3][4][5][6][7][8][9][10][11][12][13][14]. However, in principle other forms for Λ are possible.…”

Section: Introductionmentioning

confidence: 99%

Signatures of non-Markovian turbulent transport in reversed field pinch plasmas

Sattin

Paccagnella

D’Angelo

2005

Physica A: Statistical Mechanics and its Applications

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“…There we used a very simplified model of the turbulent potential structures, namely a spatially periodic and time-independent potential. Using a Hamiltonian approach (which takes into account the cyclotron motion), we have found, for impurity ions C + and usual potential amplitudes, a substantial increase in the diffusion of these ions (both of the Gaussian and Lévy-walk forms) [4], resulting in the generation of a radial electric field [3]. Using a drift approximation for this case, no diffusion and no electric field is observed.…”

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confidence: 99%

Anomalous diffusion and radial electric field generation due to edge plasma turbulence

Pánek¹,

Krlín

Tskhakaya

et al. 2004

Contrib. Plasma Phys.

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It is generally accepted that tokamak edge plasma turbulence causes anomalous diffusion. Theoretical studies addressing the anomalous diffusion in these potential structures are usually based on the test-particle drift approximation and on the electrostatic field resulting from the Hasegawa-Mima model (see, e.g. [1]) or the Hasegawa-Wakatani model [2].In our preceding papers (e.g.[3]), we discussed the effect of the anomalous ion diffusion in question on radial electric field generation. There we used a very simplified model of the turbulent potential structures, namely a spatially periodic and time-independent potential. Using a Hamiltonian approach (which takes into account the cyclotron motion), we have found, for impurity ions C + and usual potential amplitudes, a substantial increase in the diffusion of these ions (both of the Gaussian and Lévy-walk forms) [4], resulting in the generation of a radial electric field [3]. Using a drift approximation for this case, no diffusion and no electric field is observed. Radial electric fields play an important role in the formation of transport barriers in tokamaks. It seems that our mechanism, resulting from anomalous diffusion of impurities can play an interesting role.Recently, a more realistic form of this potential, namely the Hasegawa-Wakatani potential (HW), was considered. The HW model [5] is based on the numerical solution of mode-coupling equations for the resistive drift-wave instability, modelling in this way the turbulent processes in the edge plasma. We have followed their approach, using the parameters of the Czech CASTOR tokamak [6] for the numerical simulation. A typical instantaneous potential relief inside a space sample with dimensions 4 cm radially 8 cm poloidally is presented in Fig. 1. We use the 2-dimensional Particle-in-Cell (PIC) code BIT2 to follow C + ions. These particles are initially distributed uniformly over the whole sample. We assume periodic boundary conditions in the poloidal direction. In the radial direction, the boundary conditions are periodic for the calculation of the variance and diffusion coefficient and non-periodic for the self-consistent calculation of the radial electric field generation. The electrons and plasma ions are treated as a fixed background and the HW potential is taken from a fluid simulation.We calculate the time histories of the average variance X 2 (t) and the running diffusion coefficient(and similarly for the y direction), where x j , y j are the radial and poloidal co-ordinates of the jth particle, respectively, t is time, and N is the number of particles. In Fig. 3 we see that the diffusion is larger in the poloidal direction than in the radial. Contrary to the results presented in [4], the diffusion in the radial direction is rather Gaussian, and only the diffusion in the poloidal direction has a parabolic-type variance time trace (Fig. 2) indicating Lévy-walk dynamics. As already proposed in our recent papers ([3], [7]), this anomalous diffusion must necessarily results in a positive-charge deficit....

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Stochastic (E×B) diffusion of ions in a spatially periodical potential field

Cited by 10 publications

References 13 publications

Anomalous impurity diffusion in models of tokamak edge plasma turbulence

Anomalous impurity diffusion in models of tokamak edge plasma turbulence

Signatures of non-Markovian turbulent transport in reversed field pinch plasmas

Anomalous diffusion and radial electric field generation due to edge plasma turbulence

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