Sheath heat transmission factors on TCV

Márki, J.; Pitts, R.A.; Eich, T.; Herrmann, A.; Horáček, J.; Sánchez, F.; Veres, G. I.

doi:10.1016/j.jnucmat.2007.01.197

Cited by 30 publications

(19 citation statements)

References 16 publications

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“…Additionally, we assume the ELM-averaged electron temperature, T e,ELM = 15 eV from earlier LP measurements in AUG [1]. As can be seen from figure 10, RFA and thermographic measurements of q // are in a fairly good agreement given the number of uncertainties in a probe-thermography comparison [43] and in calculating q // from probe data [44]. Moreover, T i,ELM from figure 9 agrees with earlier estimates of T i,ELM in the AUG SOL, obtained from the first RFA measurements in AUG and from 2-d IR thermography [24,35].…”

Section: Far Sol Elm Ion Energiesmentioning

confidence: 83%

Intermittent transport across the scrape-off layer: latest results from ASDEX Upgrade

et al. 2013

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Abstract.We report the latest results of turbulence and transport studies in the ASDEX Upgrade scrapeoff layer (SOL). Dissimilarity between the plasma and the floating potential fluctuations is studied experimentally and by gyrofluid simulations. Measurements by a retarding field analyzer reveal that both, ELM and turbulent filaments convey hot ions over large radial distances in the SOL. The measured far SOL ELM ion temperature increases with the ELM energy, consistent with earlier observations that large ELMs deposit a large fraction of their energy outside the divertor. In the SOL, the ELM suppression by magnetic perturbations (MPs) results into lower ELM ion energy in the far SOL. At the same time, large filaments of ion saturation current are replaced by more continuous bursts. Splitting of the divertor strike zones observed by the infrared imaging in H-mode with MPs agree with predictions from the EMC3-Eirene simulations. This suggests that the 'lobe' structures due to perturbation fields observed near the X-point are not significantly affected by plasma screening, and can be described by a vacuum approach, as in the EMC3-Eirene. Finally, some effects of the MPs on the L-mode SOL are addressed.

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Section: Far Sol Elm Ion Energiesmentioning

confidence: 83%

Intermittent transport across the scrape-off layer: latest results from ASDEX Upgrade

et al. 2013

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“…This is based on observations that the probe heat flux is larger than theory would suggest during a death-ray. The sheath heat flux anomaly has been seen elsewhere [6], yet this was the first time it was connected to the death-ray overpressure. This phenomenon is the main subject of numerical simulations described in this paper.…”

Section: Introductionmentioning

confidence: 79%

Modeling of Local Edge Plasma Perturbations Induced by a Biased Probe

Umansky

Brunner

LaBombard

et al. 2012

Contrib. Plasma Phys.

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The Langmuir probe is a standard diagnostic tool for laboratory plasmas, routinely used for edge plasmas in magnetic fusion devices. However, recent studies on the Alcator C-Mod tokamak indicate the possibility of a substantial local plasma perturbation by a negatively biased divertor plate target probe under high recycling conditions when the electron temperature is under ∼10 eV. The effects of the probe perturbation of the plasma are studied using the tokamak edge plasma code UEDGE for parameters relevant to Alcator C-Mod edge. It is found that at sufficiently negative bias voltage, the probe substantially modifies the local plasma characteristics. In particular, this is relevant to the experimentally known "death-ray" phenomenon, where the plasma pressure near the probe strongly exceeds the upstream value. Certain features of the "death-ray" phenomenon are reproduced in the modeling, pointing to interplay of plasma and neutrals transport, atomic physics, and sheath heat-flux boundary conditions.

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“…According to the Bohm condition, the Mach number should be at least unity at the sheath edge. The heat transmission coefficients should fall within the range γ i = 2 ∼ 3 and γ e = 4.5 ∼ 5.5 as given by [22], although experiments show that this range is too restricted [32]. Since the plasma is magnetized, it has two degrees of freedom, and therefore the adiabatic index should be approximately 2.…”

Section: Summary Of Kinetic Factorsmentioning

confidence: 96%

Kinetic Particle Simulation Study of Parallel Heat Transport in Scrape-off Layer Plasmas over a Wide Range of Collisionalities

Froese

Takizuka

Yagi

2010

Plasma and Fusion Research

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Fluid models are not generally applicable to fusion edge plasmas without external provision of kinetic factors: closure parameters and boundary conditions inside the sheath region. We explain the PARASOL-1D simulation, a particle-in-cell code with a binary collision Monte-Carlo model, and use it to determine four kinetic factors commonly needed in fluid codes. These are the electron and ion heat flux limiting factors, α e and α i , the ion adiabatic index, γ A , and the electron and ion temperature anisotropy, T || /T ⊥ . We survey these factors over a wide range of collisionalities and find that, as predicted, the conductive heat flux is accurately described by the Spitzer-Härm expression in the collisional limit and asymptotes to a constant value in the collisionless limit. However, unique behavior occurs in the weakly collisional regime when the ratio of the mean free path to connection length is 0.1 < λ mfp /L || < 10, when the SOL is between the conduction-and sheath-limited regimes. We find that α e can peak, becoming larger than the collisionless limit, γ A is less than unity, and only the ions are anisotropic. The effects of electron energy radiation and Langevin heating are explored. Finally, the strong deviations of the energy distribution function from Maxwellian in the weakly collisional and collisionless regimes are explained.

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Sheath heat transmission factors on TCV

Cited by 30 publications

References 16 publications

Intermittent transport across the scrape-off layer: latest results from ASDEX Upgrade

Intermittent transport across the scrape-off layer: latest results from ASDEX Upgrade

Modeling of Local Edge Plasma Perturbations Induced by a Biased Probe

Kinetic Particle Simulation Study of Parallel Heat Transport in Scrape-off Layer Plasmas over a Wide Range of Collisionalities

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