Trapping, Anomalous Transport, and Quasi-coherent Structures in Magnetically Confined Plasmas

Abstract The anomalous transport in magnetically confined plasmas is investigated by the radial fractional transport equations. It is shown that for fractional transport models, hollow density profiles are formed and uphill transports can be observed regardless of whether the fractional diffusion coefficients (FDCs) are radially dependent or not. When a radially dependent FDC Dα(r)<1 is imposed, compared with the case under Dα(r)=1.0, it is observed that the position of the peak of the density profile is closer to the core. Besides, it is found that when FDCs at the positions of source injections increase, the peak values of density profiles decrease. The non-local effect becomes significant as the order of fractional derivative α→1 and causes the uphill transport. However, as α→2, the fractional diffusion model returns to the standard model governed by Fick’s law.

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Spatial inhomogeneity effects on burst temperature estimation using a triple probe configuration in Tokamak Chauffage Alfvén Brésilien tokamak

Journal of Plasma Physics ◽

10.1017/s0022377819000503 ◽

2019 ◽

Vol 85 (4) ◽

Cited By ~ 1

Author(s):

W. A. Hernandez ◽

Z. O. Guimarães-Filho ◽

G. G. Grenfell ◽

I. C. Nascimento

Keyword(s):

Coherent Structures ◽

Plasma Sheath ◽

Spatial Inhomogeneity ◽

Langmuir Probes ◽

Temperature Estimation ◽

Probe Technique ◽

Confined Plasmas ◽

Magnetically Confined ◽

Time Trace ◽

Magnetically Confined Plasmas

The effects of coherent structures in plasma edge turbulence are an important topic in the study of plasma cross-field transport in magnetically confined plasmas. To properly characterize these structures, their temperature must be measured, which is often done by using Langmuir probes. In this work, the techniques of Langmuir sweep and triple probe are used, considering the effect of plasma sheath expansion in both methods. It is shown that if the sheath expansion is ignored, the triple probe technique gives overestimated temperature values. In addition, the conditional analysis is applied to both techniques in order to evaluate the mean temperature time trace of the coherent structures. It is shown that these time traces can be distorted in the case of the triple probe technique, due to fact that coherent structures destroy the homogeneity condition on the pins array. Therefore, the sweep technique with a conditional selection of points is more suitable than the triple probe to study coherent structures related to bursts, as it performs a local measurement.

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Negative Energy Waves in the Frame work of Vlasov -Maxwell Theory

Zeitschrift für Naturforschung A ◽

10.1515/zna-1988-0603 ◽

1988 ◽

Vol 43 (6) ◽

pp. 533-537 ◽

Cited By ~ 1

Author(s):

Dieter Pfirsch

Keyword(s):

Variational Formulation ◽

Negative Energy ◽

Anomalous Transport ◽

Magnetized Plasmas ◽

Maxwell Theory ◽

Confined Plasmas ◽

Particle Species ◽

Magnetically Confined ◽

Frame Work ◽

Magnetically Confined Plasmas

Abstract On the basis of a variational formulation of the Vlasov-Maxwell theory it was recently shown that, for instance, all magnetically confined plasmas allow the existence of negative energy waves. Such waves can become nonlinearly and dissipatively unstable and might therefore be of importance in explaining anomalous transport. The proof of this result uses infinitely strongly localized perturbations. This is, however, not necessary: in this paper it is shown by discussing general, homogeneous, magnetized plasmas that the necessary localization is related to the average gyroradius rg of the relevant particle species. For unstable plasmas the extent or wavelengths of negative energy waves can be of the order of rg, whereas for linearly stable plasmas the extent can be a small fraction of rg.

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