The impact of edge radial electric fields on edge–scrape-off layer coupling in the TJ-II stellarator

Grenfell, G.; Losada, U.; Estrada, T.; Liu, B.; Silva, Carlos; Spolaore, M.; Hidalgo, C.

doi:10.1088/1741-4326/ab538c

Cited by 19 publications

(25 citation statements)

References 25 publications

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“…The drop of λ Is (which is closed related to the density decay length around the the LCFS, λ n ) indicates that the profile becomes steeper during biasing (H-mode), and it follows the trend of L * r , in qualitative agreement with the mixing length hypothesis ñ/ n ∼ L * r /λ n , since ñ/ n ∼ Ĩs / I s ∼ 0.2 around the LCFS before and during biasing. The disagreement in the absolute value is partially due to the definition of the mixing length here, i.e., from the maximum of the correlation instead of at zero delay that naturally gives larger values [23]. Nevertheless, this result shows that the relaxation of the I s profile is related to wider penetration of turbulence in the SOL, leading to a larger mixing length.…”

Section: E × B Background Flowmentioning

confidence: 81%

Turbulent filament properties in L and H-mode regime in the RFX-mod operating as a tokamak

et al. 2020

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The dynamics of turbulent filaments in L and ELM-free H-mode in the RFX-mod device operating as a tokamak is discussed in the present work. L-H transition and sustained H-mode have been achieved in the RFX-mod with the aid of an external electrode biasing (M. Spolaore et al. 2017 Nucl. Fusion 57 116039). Through advanced statistical techniques, turbulent filaments are detected and tracked from the edge to the Scrape-Off Layer (SOL) in a two-dimension floating potential map (measured with a 2D array of Langmuir probes) related with extreme events of a fixed ion saturation current signal in the SOL. While in L-mode filaments travel almost freely, their motion becomes restricted to the near SOL during the induced biasing H-mode. In this region, the background shear decorrelation time becomes shorter than the convective filament time, favouring its suppression. However, the experimental observation of a nearly 'trapped' monopole potential points out the possible role of the vortex selection mechanism. The sign and magnitude of the turbulent parallel vorticity are consistent with the E × B background vorticity in the SOL in this regime, while in L-mode, the inferred turbulent vorticity is always above the background one. The sparse filamentary transport in the far SOL during H-mode is further confirmed from the measurements of a poloidally symmetric array of electrostatic sensors on the wall. Lastly, the radial velocity of filaments in both regimes was discussed in the framework of analytical scalings. Filaments in L-mode exhibit a reasonable agreement with the sheath-limited regime in the cold ion approximation, with a non-negligible associated parallel current density measured with a set of 3-axial pickup coils installed in the probe head. In H-mode, the collisionality increases near the separatrix while filaments seem to follow the inertial regime before becoming trapped.

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Section: E × B Background Flowmentioning

confidence: 81%

Turbulent filament properties in L and H-mode regime in the RFX-mod operating as a tokamak

et al. 2020

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“…Turbulence spreading 36 – 38 is expected to play an important role for the evolution of an MI 39 , since the accompanying heat or particle flux can change the pressure and current profile inside the MI. Detailed observation of the dynamics of turbulence spreading would be helpful to understand its effect on the MI evolution.…”

Section: Resultsmentioning

confidence: 99%

Effects of plasma turbulence on the nonlinear evolution of magnetic island in tokamak

et al. 2021

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Magnetic islands (MIs), resulting from a magnetic field reconnection, are ubiquitous structures in magnetized plasmas. In tokamak plasmas, recent researches suggested that the interaction between an MI and ambient turbulence can be important for the nonlinear MI evolution, but a lack of detailed experimental observations and analyses has prevented further understanding. Here, we provide comprehensive observations such as turbulence spreading into an MI and turbulence enhancement at the reconnection site, elucidating intricate effects of plasma turbulence on the nonlinear MI evolution.

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“…2017; Grenfell et al. 2019), which is difficult to properly model with a simulation domain that does not include all of them. As a consequence, we perform turbulence simulations of the whole tokamak in order to approach this interplay.…”

Section: Introductionmentioning

confidence: 99%

“…a lower single-null configuration, while retaining the coupling between the edge and both the core and the scrape-off layer (SOL), as a crucial element in determining the plasma dynamics at the tokamak edge. In fact, the transport mechanisms occurring in the tokamak periphery are expected to result from a complex interplay among core, edge and SOL physics (Fichtmüller, Corrigan & Simonini 1998;Dif-pradalier et al 2017;Grenfell et al 2019), which is difficult to properly model with a simulation domain that does not include all of them. As a consequence, we perform turbulence simulations of the whole tokamak in order to approach this interplay.…”

Section: Introductionmentioning

confidence: 99%

Investigation of turbulent transport regimes in the tokamak edge by using two-fluid simulations

Giacomin

Ricci

2020

J. Plasma Phys.

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The results of flux-driven, two-fluid simulations in single-null configurations are used to investigate the processes determining the turbulent transport in the tokamak edge. Three turbulent transport regimes are identified: (i) a developed transport regime with turbulence driven by an interchange instability, which shares a number of features with the standard L-mode of tokamak operation; (ii) a suppressed transport regime, characterized by a higher value of the energy confinement time, low-amplitude relative fluctuations driven by a Kelvin–Helmholtz instability, a strong $\boldsymbol {E}\times \boldsymbol {B}$ sheared flow and the formation of a transport barrier, which recalls the H-mode; and (iii) a degraded confinement regime, characterized by a catastrophically large interchange-driven turbulent transport, which recalls the crossing of the Greenwald density limit. We derive an analytical expression of the pressure gradient length in the three regimes. The transition from the developed transport regime to the suppressed transport regime is obtained by increasing the heat source or decreasing the collisionality and vice versa for the transition from the developed transport regime to the degraded confinement regime. An analytical expression of the power threshold to access the suppressed transport regime, linked to the power threshold for H-mode access, as well as the maximum density achievable before entering the degraded confinement regime, related to the Greenwald density, are also derived. The experimental dependencies of the power threshold for H-mode access on density, tokamak major radius and isotope mass are retrieved. The analytical estimate of the density limit contains the correct dependence on the plasma current and on the tokamak minor radius.

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The impact of edge radial electric fields on edge–scrape-off layer coupling in the TJ-II stellarator

Cited by 19 publications

References 25 publications

Turbulent filament properties in L and H-mode regime in the RFX-mod operating as a tokamak

Turbulent filament properties in L and H-mode regime in the RFX-mod operating as a tokamak

Effects of plasma turbulence on the nonlinear evolution of magnetic island in tokamak

Investigation of turbulent transport regimes in the tokamak edge by using two-fluid simulations

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