High density limit in reversed field pinches

Puiatti, M. E.; Scarin, P.; Spizzo, G.; Valisa, M.; Paccagnella, R.; Predebon, I.; Agostini, M.; Alfier, A.; Canton, A.; Cappello, S.; Carraro, L.; Gazza, E.; Innocente, P.; Lorenzini, R.; Marrelli, L.; Terranova, D.

doi:10.1063/1.3063060

Cited by 35 publications

(67 citation statements)

References 53 publications

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“…Analogies have already been found between the tokamak and the RFP as long as edge physics [117], the Greenwald limit [15,118], and internal transport barriers (ITB) [68] are concerned. Furthermore the RFP is an excellent test bed for the efficient control of multiple resistive wall modes [14,82].…”

Section: Resultsmentioning

confidence: 97%

What is a Reversed Field Pinch?

Escande¹

2015

Rotation and Momentum Transport in Magnetized Plasmas

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Section: Resultsmentioning

confidence: 97%

What is a Reversed Field Pinch?

Escande¹

2015

Rotation and Momentum Transport in Magnetized Plasmas

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“…Actually, the equipotential surfaces already define the shape of the convective cell measured by the GPI in RFX, and thẽ E ÂB flow can be defined as the motion of electrons and ions along the equipotential surfaces,ṽ EÂB Á rU ¼ 0, that conserves kinetic energy and can drive the macroscopic transport features which are seen near the Greenwald limit. [15][16][17] The presence of the convective cell is made evident by differentiating Eq. (3), and obtaining the map of (E f , E w p ), shown in Fig.…”

Section: The Ambipolar Modelmentioning

confidence: 99%

“…In the RFX, evidence of a causal connection between the convective cell and the MARFE (and thus, the Greenwald limit) is compelling. [15][16][17] To better understand the topology of the E r field, we can map the measured values (as a function of u) onto an edge flux surface calculated with VMEC/V3FIT: the adaptation of VMEC to the reversed field pinch is a recent addition in the framework of a collaboration between Consorzio RFX and the Auburn University. 34 The result is shown in Fig.…”

Section: The Experimental Basismentioning

confidence: 99%

“…In the RFX-mod reversed field pinch 14 (major radius R ¼ 2 m, minor radius a ¼ 0.5 m), there is a large body of evidence that the flow associated with the edge 0/1 island is ultimately responsible for an edge density peaking which drives the Greenwald limit. [15][16][17] In this paper, we will describe an analytical model of the ambipolar potential response to an edge magnetic island, Invited speaker. c) Electronic address: gianluca.spizzo@igi.cnr.it which has been introduced in test-particle simulations with the guiding-center code ORBIT.…”

Section: Introductionmentioning

confidence: 99%

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Edge ambipolar potential in toroidal fusion plasmas

Spizzo¹,

Vianello²,

White³

et al. 2014

Physics of Plasmas

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A series of issues with toroidally confined fusion plasmas are related to the generation of 3D flow patterns by means of edge magnetic islands, embedded in a chaotic field and interacting with the wall. These issues include the Greenwald limit in Tokamaks and reversed-field pinches, the collisionality window for ELM mitigation with the resonant magnetic perturbations (RMPs) in Tokamaks, and edge islands interacting with the bootstrap current in stellarators. Measurements of the 2D map of the edge electric field E r ðr ¼ a; h; /Þ in the RFX reversed-field pinch show that E r has the same helicity of the magnetic islands generated by a m/n perturbation: in fact, defining the helical angle u ¼ mh À n/ þ xt, maps show a sinusoidal dependence as a function of u, E r ¼Ẽ r sin u. The associated E Â B flow displays a huge convective cell with vðaÞ 6 ¼ 0 which, in RFX and near the Greenwald limit, determines a stagnation point for density and a reversal of the sign of E r . From a theoretical point of view, the question is how a perturbed toroidal flux of symmetry m/n gives rise to an ambipolar potential U ¼Ũsin u. On the basis of a model developed with the guiding center code ORBIT and applied to RFX and the TEXTOR tokamak, we will show that the presence of an m/n perturbation in any kind of device breaks the toroidal symmetry with a drift proportional to the gyroradius q, thus larger for ions (q i ) q e ). Immediately, an ambipolar potential arises to balance the drifts, with the same symmetry as the original perturbation.

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“…Several papers have been published to provide tentative explanations of the phenomenon. Unfortunately, to the best of the author's knowledge, none of these theories works for the RFP where the same limit is present [106,107], but this has been overlooked by tokamak experts.…”

Section: Time For Creative Thinking and Non Purpose-oriented Researchmentioning

confidence: 99%

How to Face the Complexity of Plasmas?

Escande

2013

Nonlinear Systems and Complexity

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This paper has two main parts. The first part is subjective and aims at favoring a brainstorming in the plasma community. It discusses the present theoretical description of plasmas, with a focus on hot weakly collisional plasmas. It comprises two sub-parts. The first one deals with the present status of this description. In particular, most models used in plasma physics are shown to have feet of clay, there is no strict hierarchy between them, and a principle of simplicity dominates the modeling activity. At any moment the description of plasma complexity is provisional and results from a collective and somewhat unconscious process. The second sub-part considers possible methodological improvements, some of them specific to plasma physics, some others of possible interest for other fields of science. The proposals for improving the present situation go along the following lines: improving the way papers are structured and the way scientific quality is assessed in the referral process, developing new data bases, stimulating the scientific discussion of published results, diversifying the way results are made available, assessing more quality than quantity, making available an incompressible time for creative thinking and non purpose-oriented research. Some possible improvements for teaching are also indicated. The suggested improvement of the structure of papers would be for each paper to have a "claim section" summarizing the main results and their most relevant connection to previous literature. One of the ideas put forward is that modern nonlinear dynamics and chaos might help revisiting and unifying the overall presentation of plasma physics.The second part of this chapter is devoted to one instance where this idea has been developed for three decades: the description of Langmuir wave-electron interaction in one-dimensional plasmas by a finite dimensional Hamiltonian. This part is more specialized, and is written like a classical scientific paper. This Hamiltonian approach enables recovering Vlasovian linear theory with a mechanical understanding. The quasilinear description of the weak warm beam is discussed, and it is shown that self-consistency vanishes when the plateau forms in the tail distribution function. This leads to consider the various diffusive regimes of the dynamics of particles in a frozen spectrum of waves with random phases. A recent numerical simulation showed that diffusion is quasilinear when the plateau sets in, and that the variation of the phase of a given wave with time is almost non fluctuating for random realizations of the initial wave phases. This led to new analytical calculations of the average behavior of the self-consistent dynamics when the initial wave phases are random. Using Picard iteration technique, they confirm numerical results, and exhibit a spontaneous emission of spatial inhomogeneities.Non quia difficilia sunt, non audemus, sed quia non audemus, difficilia sunt. It is not because things are difficult that we do not dare, it is because we do not dare that things a...

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High density limit in reversed field pinches

Cited by 35 publications

References 53 publications

What is a Reversed Field Pinch?

What is a Reversed Field Pinch?

Edge ambipolar potential in toroidal fusion plasmas

How to Face the Complexity of Plasmas?

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