Overview of quasi-single helicity experiments in reversed field pinches

Martin, P.; Marrelli, L.; Spizzo, G.; Franz, P.; Piovesan, P.; Predebon, I.; Bolzonella, T.; Cappello, S.; Cravotta, A.; Escande, Dominique; Frassinetti, L.; Ortolani, S.; Paccagnella, R.; Terranova, D.; Chapman, B.E.; Craig, D.; Prager, S. C.; Sarff, J. S.; Brunsell, Per R.; Malmberg, Jenny-Ann; Drake, James R.; Yagi, Y.; Koguchi, Haruhisa; Hirano, Y.; White, R. B.; Sovinec, C. R.; Xiao, C.; Nebel, Richard; Schnack, D. D.

doi:10.1088/0029-5515/43/12/028

Cited by 105 publications

(82 citation statements)

References 34 publications

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“…The substitutions D ¼ D eq þD and S ¼ S eq þS are made in Eqs. (1) and (2), and assumingD andS are small, the equations are linearized to obtain A ¼…”

Section: B Phase Analysismentioning

confidence: 99%

“…11 and 23 that were also used in the derivation of Eqs. (1) and (2). Thus, displacements are normalized by the minor radius a, time by s A ¼ a/V A , where V A is the Alfven velocity of an equilibrium magnetic field B 0 , w by aB 0 and / by a 2 B 0 =s A .…”

Section: Temperature Evolutionmentioning

confidence: 99%

“…1 A revealing feature of the self-organized dynamics is the quasi-single helicity (QSH) state, in which the normally broad-band magnetic fluctuation spectrum undergoes a transition to a spectrum dominated by a single helical mode. 2,3 Theoretically, QSH transitions can either be induced or occur spontaneously. Induced transitions can be triggered by reducing the Hartmann number 4 in a process that leaves a single dominant helical mode en route to a viscous laminarization of the turbulence.…”

Section: Introductionmentioning

confidence: 99%

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Thermal transport dynamics in the quasi-single helicity state

McKinney

Terry

2017

Physics of Plasmas

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A dynamical model describing oscillations between multiple and single helicity configurations in the quasi-single helicity (QSH) state of the reversed field pinch [P. W. Terry and G. G. Whelan, Plasma Phys. Controlled Fusion 56, 094003 (2014)] is extended to include electron temperature profile dynamics. It is shown that QSH dynamics is linked to the electron temperature profile because the suppression of mode coupling between tearing modes proposed to underlie QSH also suppresses magnetic-fluctuation-induced thermal transport. Above the threshold of dominant-mode shear that marks the transition to QSH, the model produces temperature-gradient steepening in the strong shear region. Oscillations of the dominant and secondary mode amplitudes give rise to oscillations of the temperature gradient. The phasing and amplitude of temperature gradient oscillations relative to those of the dominant mode are in agreement with experiment. This provides further evidence that the model, while heuristic, captures key physical aspects of the QSH state.

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“…The substitutions D ¼ D eq þD and S ¼ S eq þS are made in Eqs. (1) and (2), and assumingD andS are small, the equations are linearized to obtain A ¼…”

Section: B Phase Analysismentioning

confidence: 99%

Section: Temperature Evolutionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermal transport dynamics in the quasi-single helicity state

McKinney

Terry

2017

Physics of Plasmas

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“…The reduction of magnetic chaos is crucial in reducing D and cancelling the pinch: this happens e.g. in the RFP approaching the single-helicity condition [4,5,7].…”

Section: A Steady State Distributionsmentioning

confidence: 99%

“…For purposes of thermonuclear fusion, the reversed field pinch (RFP) [4,5] is of interest particularly because of the existence of single helicity states [6,7], which offer good confinement (for a recent review of the results on single helicity see [8]). However at low current the normal state of the RFP is the multi-helicity state, dominated by a known but large spectrum of relatively stable saturated tearing modes.…”

Section: Introductionmentioning

confidence: 99%

Nonlocal Transport in the Reversed Field Pinch

Spizzo¹,

White²,

Cappello³

et al. 2009

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Several heuristic models for nonlocal transport in plasmas have been developed, but they have had a limited possibility of detailed comparision with experimental data. Nonlocal aspects introduced by the existence of a known spectrum of relatively stable saturated tearing modes in a low current reversed field pinch offers a unique possibility for such a study. A numerical modelling of the magnetic structure and associated particle transport is carried out for the reversed-field pinch experiment at the Consorzio RFX, Padova, Italy. A reproduction of the tearing mode spectrum with a guiding center code 1 reliably reproduces the observed soft X-ray tomography. Following particle trajectories in the stochastic magnetic field shows the transport across the unperturbed flux surfaces to be due to a spectrum of Lévy flights, with the details of the spectrum position dependent. The resulting transport is subdiffusive, and cannot be described by Rechester-Rosenbluth diffusion, which depends on a random phase approximation. If one attempts to fit the local transport phenomenologically, the subdiffusion can be fit with a combination of diffusion and inward pinch 2 . It is found that whereas passing particles explore the stochastic field and hence participate in Lévy flights, the trapped particles experience normal neoclassical diffusion.A two fluid nonlocal Montroll equation is used to model this transport, with a Lévy flight defined as the motion of an ion during the period that the pitch has one sign. The necessary input to the Montroll equation consists of a time distribution for the Lévy flights, given by the pitch angle scattering operator, and a distribution of the flight distances, determined numerically using a guiding center code. Results are compared to experiment. The relation of this formulation to fractional kinetics is also described.

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