The Radial Propagation of Heat in Strongly Driven Non-Equilibrium Fusion Plasmas

Heat transport is studied in strongly heated fusion plasmas, far from thermodynamic equilibrium. The radial propagation of perturbations is studied using a technique based on the transfer entropy. Three different magnetic confinement devices are studied, and similar results are obtained. “Minor transport barriers” are detected that tend to form near rational magnetic surfaces, thought to be associated with zonal flows. Occasionally, heat transport “jumps” over these barriers, and this “jumping” behavior seems to increase in intensity when the heating power is raised, suggesting an explanation for the ubiquitous phenomenon of “power degradation” observed in magnetically confined plasmas. Reinterpreting the analysis results in terms of a continuous time random walk, “fast” and “slow” transport channels can be discerned. The cited results can partially be understood in the framework of a resistive Magneto-HydroDynamic model. The picture that emerges shows that plasma self-organization and competing transport mechanisms are essential ingredients for a fuller understanding of heat transport in fusion plasmas.

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Impurity transport and bulk ion flow in a mixed collisionality stellarator plasma

Journal of Plasma Physics ◽

10.1017/s0022377817000745 ◽

2017 ◽

Vol 83 (5) ◽

Cited By ~ 11

Author(s):

S. L. Newton ◽

P. Helander ◽

A. Mollén ◽

H. M. Smith

Keyword(s):

Fusion Energy ◽

Effect Of Temperature ◽

Fusion Plasmas ◽

Ion Flow ◽

Confined Plasmas ◽

Impurity Species ◽

Magnetically Confined ◽

Bootstrap Current ◽

Magnetically Confined Plasmas ◽

Bulk Plasma

The accumulation of impurities in the core of magnetically confined plasmas, resulting from standard collisional transport mechanisms, is a known threat to their performance as fusion energy sources. Whilst the axisymmetric tokamak systems have been shown to benefit from the effect of temperature screening, that is an outward flux of impurities driven by the temperature gradient, impurity accumulation in stellarators was thought to be inevitable, driven robustly by the inward pointing electric field characteristic of hot fusion plasmas. We have shown in Helander et al. (Phys. Rev. Lett., vol. 118, 2017a, 155002) that such screening can in principle also appear in stellarators, in the experimentally relevant mixed collisionality regime, where a highly collisional impurity species is present in a low collisionality bulk plasma. Details of the analytic calculation are presented here, along with the effect of the impurity on the bulk ion flow, which will ultimately affect the bulk contribution to the bootstrap current.

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Plasma networking in magnetically confined plasmas and diagnostics of nonlocal heat transport in tokamak filamentary plasmas

Review of Scientific Instruments ◽

10.1063/1.1149577 ◽

1999 ◽

Vol 70 (2) ◽

pp. 1392-1396 ◽

Cited By ~ 2

Author(s):

A. B. Kukushkin ◽

V. A. Rantsev-Kartinov

Keyword(s):

Heat Transport ◽

Confined Plasmas ◽

Magnetically Confined ◽

Magnetically Confined Plasmas

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Shearless transport barriers in magnetically confined plasmas

Plasma Physics and Controlled Fusion ◽

10.1088/0741-3335/54/12/124035 ◽

2012 ◽

Vol 54 (12) ◽

pp. 124035 ◽

Cited By ~ 8

Author(s):

I L Caldas ◽

R L Viana ◽

C V Abud ◽

J C D Fonseca ◽

Z O Guimarães Filho ◽

...

Keyword(s):

Confined Plasmas ◽

Magnetically Confined ◽

Transport Barriers ◽

Magnetically Confined Plasmas

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On the accuracy of the binary-collision algorithm in particle-in-cell simulations of magnetically confined fusion plasmas

Journal of Plasma Physics ◽

10.1017/s0022377821000398 ◽

2021 ◽

Vol 87 (2) ◽

Author(s):

Timo P. Kiviniemi ◽

Eero Hirvijoki ◽

Antti J. Virtanen

Keyword(s):

Finite Difference ◽

Electric Fields ◽

Finite Size ◽

Binary Collision ◽

Conserved Quantities ◽

Fusion Plasmas ◽

Fusion Plasma ◽

Particle In Cell ◽

Magnetically Confined ◽

Scale Length

Ideally, binary-collision algorithms conserve kinetic momentum and energy. In practice, the finite size of collision cells and the finite difference in the particle locations affect the conservation properties. In the present work, we investigate numerically how the accuracy of these algorithms is affected when the size of collision cells is large compared with gradient scale length of the background plasma, a parameter essential in full- $f$ fusion plasma simulations. Additionally, we discuss implications for the conserved quantities in drift-kinetic formulations when fluctuating magnetic and electric fields are present: we suggest how the accuracy of the algorithms could potentially be improved with minor modifications.

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