A model for electron transport barriers in tokamaks, tested against experimental data from RTP

Hogeweij, G. M. D.; Cardozo, N.J. Lopes; Baar, M.R. de; Schilham, Arnold M. R.

doi:10.1088/0029-5515/38/12/312

Cited by 76 publications

(115 citation statements)

References 32 publications

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“…This finding can in turn be helpful to build transport models like the q-comb model [23], [24]. From experimental considerations, such models define indeed barriers are localized around main rational q-values, but the width if the barriers has still to be defined.…”

Section: Experimental Localization Of Barriers In the Tokamak Q -Profilementioning

confidence: 99%

Noble internal transport barriers and radial subdiffusion of toroidal magnetic lines

et al. 2003

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Keywords : Tokamak, dynamical system, transport barrier, symplectic mappings, Hamiltonian systems, toroidal magnetic field, subdiffusion, Cantori, noble numbers, plasma confinement, scaling laws Internal transport barriers (ITB's) observed in tokamaks are described by a purely magnetic approach. Magnetic line motion in toroidal geometry with broken magnetic surfaces is studied from a previously derived Hamiltonian map in situation of incomplete chaos. This appears to reproduce in a realistic way the main features of a tokamak, for a given safety factor profile and in terms of a single parameter L representing the amplitude of the magnetic perturbation. New results are given concerning the Shafranov shift as function of L. The phase space (ψ, θ) of the "tokamap" describes the poloidal section of the line trajectories, where ψ is the toroidal flux labelling the surfaces. For small values of L, closed magnetic surfaces exist (KAM tori) and island chains begin to appear on rational surfaces for higher values of L, with chaotic zones around hyperbolic points, as expected. Island remnants persist in the chaotic domain for all relevant values of L at the main rational q-values.Single trajectories of magnetic line motion indicate the persistence of a central protected plasma core, surrounded by a chaotic shell enclosed in a double-sided transport barrier : the latter is identified as being composed of two Cantori located on two successive "most-noble" numbers values of the perturbed safety factor, and forming an internal transport barrier (ITB). Magnetic lines which succeed to escape across this barrier begin to wander in a wide chaotic sea extending up to a very robust barrier (as long as L 1) which is identified mathematically as a robust KAM surface at the plasma edge. In this case the motion is shown to be intermittent, with long stages of pseudo-trapping in the chaotic shell, or of sticking around island remnants, as expected for a continuous time random walk.For values of L 1, above the escape threshold, most magnetic lines succeed to escape out of the external barrier which has become a permeable Cantorus. Statistical analysis of a large number of trajectories, representing the evolution of a bunch of magnetic lines, indicate that the flux variable ψ asymptotically grows in a diffusive * E-mail : j.misguich@cea.fr 1 manner as (L 2 t) with a L 2 scaling as expected, but that the average radial position rm(t) asymptotically grows as (L 2 t) 1/4 while the mean square displacement around this average radius asymptotically grows in a subdiffusive manner as (L 2 t) 1/2 . This result shows the slower dispersion in the present incomplete chaotic regime, which is different from the usual quasilinear diffusion in completely chaotic situations. For physical times tϕ of the order of the escape time defined by xm(tϕ) ∼ 1, the motion appears to be superdiffusive, however, but less dangerous than the generally admitted quasi-linear diffusion. The orders of magnitude of the relevant times in Tore Supra are finally discus...

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Section: Experimental Localization Of Barriers In the Tokamak Q -Profilementioning

confidence: 99%

Noble internal transport barriers and radial subdiffusion of toroidal magnetic lines

et al. 2003

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“…Those sharp transitions corresponded to changes in the q profile, where q min jumped across a low-order rational value, eg 1, 4/3, 3/2, 2, 5/2, and 3. This indicated that χ e was a direct function of q, with transport barriers occurring near low-order rational values of q and with high values of χ e elsewhere [96,97]. Five medium density discharges representative of the main T e profile levels, from q min < 1 to q min > 3, are included in PR08 (shots #97052248, #97052263, #97052261, #97053056 and #97052270).…”

Section: Rtpmentioning

confidence: 99%

The 2008 Public Release of the International Multi-tokamak Confinement Profile Database

et al. 2008

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Abstract. This paper documents the public release PR08 of the International Tokamak Physics Activity (ITPA) profile database, which should be of particular interest to the magnetic confinement fusion community. Data from a wide variety of interesting discharges from many of the world's leading tokamak experiments are now made available in PR08, which also includes predictive simulations of an initial set of operating scenarios

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“…At present several possible mechanisms, like an ExB flow shear, a zonal flow, or a magnetic shear, have been proposed. One of these issues is the role of low-order magnetic surfaces in the formation transport barriers which have been discussed in a number of works [12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Chaotic transport in Hamiltonian systems perturbed by a weak turbulent wave field

Abdullaev

2011

Phys. Rev. E

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Chaotic transport in a Hamiltonian system perturbed by a weak turbulent wave field is studied. It is assumed that a turbulent wave field has a wide spectrum containing up to thousands of modes whose phases are fluctuating in time with a finite correlation time. To integrate the Hamiltonian equations a fast symplectic mapping is derived. It has a large time-step equal to one full turn in angle variable. It is found that the chaotic transport across tori caused by the interactions of small-scale resonances have a fractal-like structure with the reduced or zero values of diffusion coefficients near low-order rational tori thereby forming transport barriers there. The density of rational tori is numerically calculated and its properties are investigated. It is shown that the transport barriers are formed in the gaps of the density of rational tori near the low-order rational tori. The dependencies of the depth and width of transport barriers on the wave field spectrum and the correlation time of fluctuating turbulent field (or the Kubo number) are studied. These numerical findings may have importance in understanding the mechanisms of transport barrier formation in fusion plasmas.

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A model for electron transport barriers in tokamaks, tested against experimental data from RTP

Cited by 76 publications

References 32 publications

Noble internal transport barriers and radial subdiffusion of toroidal magnetic lines

Noble internal transport barriers and radial subdiffusion of toroidal magnetic lines

The 2008 Public Release of the International Multi-tokamak Confinement Profile Database

Chaotic transport in Hamiltonian systems perturbed by a weak turbulent wave field

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