Identification of the primary processes that lead to the drop in divertor target ion current at detachment in TCV

Fil, A.; Dudson, B.; Lipschultz, B.; Moulton, D.; Verhaegh, K.; Février, O.; Wensing, M.

doi:10.1002/ctpp.201700171

Cited by 26 publications

(99 citation statements)

References 11 publications

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“…This makes sense because target T e 1.2eV at this higher upstream density, whereas at target flux rollover target T e 3.2eV. This is in contrast to some previous results [33] in which flux rollover occurred at lower temperatures, but in agreement with recent experiments [34,18] and simulations [35] of TCV. There are several ways in which target flux can be reduced, recombination being one of them, so discrepancies may be seen between studies in different regimes.…”

Section: The Role Of Particle and Energy Losssupporting

confidence: 85%

The role of particle, energy and momentum losses in 1D simulations of divertor detachment

Dudson

Allen

Body

et al. 2019

Plasma Phys. Control. Fusion

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A new 1D divertor plasma code, SD1D, has been used to examine the role of recombination, radiation, and momentum exchange in detachment. Neither momentum or power losses by themselves are found to be sufficient to produce a reduction in target ion flux in detachment (flux rollover); radiative power losses are required to a) limit and reduce the ionization source and b) access low-target temperature, T target , conditions for volumetric momentum losses. Recombination is found to play little role at flux rollover, but as T target drops to temperatures around 1eV, it becomes a strong ion sink. In the case where radiative losses are dominated by hydrogen, the detachment threshold is identified as a minimum gradient of the energy cost per ionisation with respect to T target . This is also linked to thresholds in T target and in the ratio of upstream pressure to power flux.A system of determining the detached condition is developed such that the divertor solution at a given T target (or lack of one) is determined by the simultaneous solution of two equations for target ion current one dependent on power losses and the other on momentum. Depending on the detailed momentum and power loss dependence on temperature there are regions of T target where there is no solution and the plasma jumps from high to low T target states. The novel analysis methods developed here provide an intuitive way to understand complex detachment phenomena, and can potentially be used to predict how changes in the seeding impurity used or recycling aspects of the divertor can be utilised to modify the development of detachment.

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Section: The Role Of Particle and Energy Losssupporting

confidence: 85%

The role of particle, energy and momentum losses in 1D simulations of divertor detachment

Dudson

Allen

Body

et al. 2019

Plasma Phys. Control. Fusion

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“…The mechanism is explained as follows: (a) the polarization electric field E p is produced as a result of the charge separation of ions and electrons by the curvature drifts (see the potential profile in Figure 2e); (b) then, the resultant E p × B drift of ions and electrons takes place in the same direction; and (c) next, the blob shape starts deforming into a mushroom shape as seen from Figure 2b and c. This may be mainly due to the Kelvin-Helmholtz instability. [22] These properties of the plasma blob are in agreement with those from other studies. [19][20][21] It should be noted that a pair of low-density and high-density region of impurity test particles has been left in the region where the blob has been formed.…”

Section: Resultssupporting

confidence: 91%

Analysis of the plasma blob formation/transport and its effects on impurity transport in the scrape‐off layer regions

Maeda

Tominaga

Yamoto

et al. 2018

Contributions to Plasma Physics

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The purpose of this study was to clarify the effects of a plasma blob on the impurity transport in the scrape‐off layer (SOL) and divertor region of fusion devices. As a first step, plasma blob formation and transport were simulated by a two‐dimensional interchange turbulence model. Its effects on impurity transport were studied by the impurity equations of motion in the trace impurity limit. The results show that a blob is produced by the interchange instability and transported radially towards the wall by the E × B drift due to the polarization electric field by the charge separation between ions and electrons inside the blob due to their magnetic drifts. The polarization electric field also induces the impurity radial E × B drift and the resultant impurity radial transport at least for impurities with a small Larmor radius in comparison with the blob size. These first results provide us with a robust basis for a more systematic study (e.g., dependence of impurity mass and charge state) and for a more quantitative evaluation of the effects of the blob on the impurity transport in the SOL and divertor region.

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“…Hence, this mechanism is not the one setting the density SOL width, which in turn limits the power SOL width as proposed by the model proposed by Goldston. [17] In consequence, it seems to point out that it is not the mechanism responsible for the q narrow feature as suggested by Kočan et al [18] In Figure 3a, the value of each temporal and toroidal point is reported as small scatter, which also permits us to remark that the heat flux profile in the SOL is highly intermittent. In particular, the maximum value of the heat flux is about 3 times the mean values at the separatrix, but this ratio goes up to more than 5 in the far SOL, thus the temporal variation of heat flux is not to be neglected.…”

Section: Power Sol Width and Narrow Feature In Anisothermal Simulationsmentioning

confidence: 50%

Turbulent heat transport in TOKAM3X edge plasma simulations

Baudoin

Tamain

Bufferand

et al. 2018

Contributions to Plasma Physics

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The recent version of the 3D fluid code TOKAM3X, including self‐consistent variation of both electron and ion temperature, is used to investigate the properties of energy turbulent structures and heat transport. We also make a comparison with the results of the isothermal equivalent simulation. The studied regime is an L‐mode‐like regime where both particle and heat transport are dominated by turbulence with Γturb/Γtot > 80% and the turbulence features are found to be similar in isothermal and anisothermal models. However, the presence of a significant shear at the separatrix in the anisothermal version modifies the penetration length of turbulent structures into the scrape‐off layer, and seems to trigger the appearance of a sharper gradient at the separatrix, reminiscent of the narrow feature observed in the experiment.

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Identification of the primary processes that lead to the drop in divertor target ion current at detachment in TCV

Cited by 26 publications

References 11 publications

The role of particle, energy and momentum losses in 1D simulations of divertor detachment

The role of particle, energy and momentum losses in 1D simulations of divertor detachment

Analysis of the plasma blob formation/transport and its effects on impurity transport in the scrape‐off layer regions

Turbulent heat transport in TOKAM3X edge plasma simulations

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