Towards a quantitative prediction of the blob detection rate

Fuchert, G.; Carralero, D.; Mänz, P.; Stroth, U.; Wolfrum, E.

doi:10.1088/0741-3335/58/5/054006

Cited by 8 publications

(6 citation statements)

References 49 publications

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“…This would be consistent with initial modelling of JET density shoulders based on the statistical nature of filaments discussed above [42]. A second shoulder formation mechanism consistent with changes in divertor recycling would be through changes in divertor and SOL E r [57,71]. More modeling of such effects could help guide experiments.…”

Section: Implications Of This Worksupporting

confidence: 70%

“…Given that separatrix densities & temperatures and core conditions were equivalent for each divertor target configuration and n e , potential shoulder mechanism a) is also unlikely to be a determining factor in shoulder formation unless SOL radial transport is affected by the change in divertor configuration; For example, later in this paper we show that changes in divertor recycling accompany changes in divertor configuration. Changes in the divertor recycling pattern could lead to changes in radial electric field which has been postulated to change turbulent filament birthrates [57].…”

Section: Main Chamber Sol Ionizationmentioning

confidence: 99%

“…Chankin et al suggest that the enhanced E r leads to turbulence shearing and easier access to H-mode [71]. Fuchert et al, although not addressing divertor effects, argue that the magnitude of E r (in the region of the separatrix) may play an important role in determining the filament birth rate and hence transport [57]. Such ideas may explain the difference between HT and VT achievement of SOL density shoulders but might not for the case of strike point sweeping effects on the upstream density shoulder.…”

Section: Divertor Neutral Processesmentioning

confidence: 99%

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Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas

et al. 2018

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The low temperature boundary layer plasma (Scrape-Off-Layer or SOL) between the hot core and the surrounding vessel determines the level of power-loading, erosion and implantation of material surfaces, and thus the viability of tokamak-based fusion as an energy source. This study explores mechanisms affecting the formation of flattened density profiles, socalled Ôdensity shouldersÕ, in the low-field side (LFS) SOL, which modify ion and neutral fluxes to surfaces Ð and subsequent erosion. We find that increases in SOL parallel resistivity, Λ div (=[L || ν ei Ω i ]/c s Ω e ), postulated to lead to shoulder growth through changes in SOL turbulence characteristics, correlates with increases in SOL shoulder amplitude, A s , only under a subset of conditions (D 2 -fuelled L-mode density scans with outer strike point on the horizontal target). Λ div fails to correlate with A s for cases of N 2 seeding or during sweeping of the strike point across the horizontal target. The limited correlation of Λ div and A s is also found for H-mode discharges.Thus, while Λ div above a threshold of ~1 may be necessary for shoulder formation and/or growth, another mechanism is required. More significantly we find that in contrast to parallel resistivity, outer divertor recycling, as quantified by the total outer divertor Balmer D α emission, I-D!, does scale with A s where Λ div does and even where Λ div fails. Divertor recycling could lead to SOL density shoulder formation through: a) reducing the parallel to the field flow (loss) of ions out of the SOL to the divertor; and b) changes in radial electric fields which lead to ExB poloidal flows

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Section: Implications Of This Worksupporting

confidence: 70%

Section: Main Chamber Sol Ionizationmentioning

confidence: 99%

Section: Divertor Neutral Processesmentioning

confidence: 99%

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Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas

et al. 2018

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“…Since blobs are generated from instabilities of wavelength 2π/k y , we expect the generation rate to be proportional to L y k y /(2π). The generation time scale has previously been proposed as determined by poloidal flow shear (Furno et al 2008b) or a combination of flow shear and mode phase velocity (D' Ippolito et al 2011;Fuchert et al 2016). In the presence of hot ions, strong E × B flow shear may be present Paruta et al 2018).…”

mentioning

confidence: 99%

Understanding the turbulent mechanisms setting the density decay length in the tokamak scrape-off layer

Beadle

Ricci

2020

J. Plasma Phys.

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Mechanisms setting the density decay in the scrape-off layer (SOL) at the outer midplane of a tokamak plasma are disentangled using two-fluid numerical simulations in a double-null magnetic configuration and analytical estimates. Typical experimental observations are retrieved, in particular increasing intermittency of the turbulence going from the near to the far SOL, which is reflected in two different density decay lengths. The decay length of the near SOL is well described as the result of transport driven by a nonlinearly saturated ballooning instability, while in the far SOL, the density decay length is described using a model of intermittent transport mediated by blobs. The analytical estimates of the decay lengths agree well with the simulation results and typical experimental values and can therefore be used to guide tokamak design and operation.

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“…Theoretical predictions of this scaling have been made 13 , 14 , 25 , 26 , 27 and tested against experimental 28 , 29 , 30 , 31 , 32 and computational results. 33 , 34 , 35 , 36 Less well understood, but under active investigation are the formation mechanisms of blobs 37 , 38 , their generation rates 39 , 40 and their size distributions. 41 Once these quantities are determined and understood, the SOL fluxes and profiles may be modeled using statistical methods.…”

Section: Introductionmentioning

confidence: 99%

Comparison of edge turbulence characteristics between DIII-D and C-Mod simulations with XGC1

Charidakos

Myra

et al. 2020

Physics of Plasmas

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The physical processes taking place at the separatrix and scrape-off layer regions are crucial for the operation of tokamaks as they govern the interaction of hot plasma with the vessel walls. Numerical modeling of the edge with state-of-the-art codes attempts to elucidate the complex interactions between neoclassical drifts, turbulence, poloidal and parallel flows that control the physical set-up of the SOL region. Here, we present post-processing analysis of simulation results from the gyrokinetic code XGC1, comparing and contrasting edge turbulence characteristics from a simulation of the DIII-D tokamak against a simulation of the Alcator C-Mod tokamak. We find that the equilibrium E × B flux across the separatrix has a similar poloidal pattern in both discharges which can be explained by ∇B-drifts and trapped ion excursions. However, collisionality is noted to play a major role in the way that it prevents local charge accumulations from having more global effects in the C-Mod case. In both cases, turbulent electron heat flux is observed to be higher than the ion one. This seems to be a universal characteristic of the tokamak edge, possibly related to the need of electrons to maintain quasineutrality through the only channel available to them for exiting the confinement. By Fourier analysis, we identify turbulent frequencies and growth rates of the dominant mode in both simulations. In the case of C-Mod, these numbers point to the presence of a drift wave. In the DIII-D case, further linear simulations with the Gene code reveal a trapped electron mode. Furthermore, using a blob detection and tracking tool, we present the amplitude and size distributions of the blobs from both simulations. The amplitude distributions are in qualitative agreement with experimental observations while the size distributions are consistent with the fact that most of the blobs are not connecting to the divertor plates and suggest that they are generated by the shearing of the turbulent modes.

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Towards a quantitative prediction of the blob detection rate

Cited by 8 publications

References 49 publications

Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas

Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas

Understanding the turbulent mechanisms setting the density decay length in the tokamak scrape-off layer

Comparison of edge turbulence characteristics between DIII-D and C-Mod simulations with XGC1

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