Analytical calculations for impurity seeded partially detached divertor conditions

Kallenbach, A.; Bernert, M.; Dux, R.; Reimold, F.; Wischmeier, M.

doi:10.1088/0741-3335/58/4/045013

Cited by 61 publications

(76 citation statements)

References 36 publications

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“…[1,2] Experiments on impurity seeding using different gases (mainly N, Ne, and Ar, more rare Kr) are performed on many machines for several years, [3][4][5][6][7][8][9][10][11][12] and they are supported by analytical models and numerical modelling. [13][14][15][16][17] It is widely accepted that as the impurty seeding rate increases, target operation regime moves from the attachment (strong heat flux density peak near the strike point) through the partial detachment (notable reduction of the heat flux density in the strike point vicinity), the pronounced detachment (notable decrease of maximal heat flux density and maximal electron temperature in the far scrape-off layer [SOL]) to the full detachment (flattening of heat flux density and electron temperature along whole target with typical values below 1 MW∕m 2 and 2 eV correspondingly). [5] The disadvantage of intensive impurity seeding is the possible impurity leakage from the divertor, which leads to the impurity penetration into the confined region and to the fuel dilution.…”

Section: Introductionmentioning

confidence: 99%

Detached regime with highly radiating X‐point: Physics and modelling

Senichenkov

Rozhansky

Shtyrkhunov

et al. 2022

Contributions to Plasma Physics

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A possibility to operate with fully detached targets and highly radiating X-point was recently demonstrated on ASDEX Upgrade, JET, and DIII-D with intensive impurity seeding (N, Ne, Ar) and feedback control. Notable feature of such a regime is the radiated power fraction of up to 90% of discharge power inside the separatrix without a confinement degradation, or even with confinement improvement (in terms of H-factor), which leads to a full detachment of both targets. Therefore, this regime might be attractive for the next generation reactor scale tokamaks like DEMO or CFETR, where most of the power should be radiated. In the present report, the recent achievements in the understanding of such regime are reviewed. The effectiveness of divertor target shielding by different impurity gases is discussed, paying attention to its first ionization potential. SOLPS-ITER modelling results illustrating the impurity flow pattern are presented, and the importance of drift flows is demonstrated. The effect of the machine size on the effectiveness of the divertor shielding by impurity radiation is discussed. It is demonstrated that in bigger machines impurity radiation is better kept in the divertor and divertor asymmetry is less pronounced. As the seeding rate increases, both targets fully detach, and neutrals start to penetrate inside the separatrix above the X-point, leading to the plasma cooling there and to the formation of an observable localized radiation spot in the X-point vicinity.The cold zone above the X-point thus behaves as an energy sink like a divertor in conventional regime, so that the perpendicular decay length of perpendicular turbulent energy flow appears to be of the order of 𝜆 q of conventional divertor.During the formation of the radiating X-point a potential hill/well (depending on the direction of B × ∇B drift) is formed on perturbed closed flux surfaces, and the corresponding E × B drift vortex fluxes appear to give major contribution to the particle balance. SOLPS-ITER simulations show that the radial electric field significantly deviates from neoclassical formula and may even change sign (become positive). Thus, the zone of maximal poloidal rotation shear may shift inwards, which might be responsible for the inward shift of the transport barrier and for the confinement improvement. This effect is different to the discussed extension of peeling-ballooning stability boundary by intensive impurity injection, which

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Section: Introductionmentioning

confidence: 99%

Detached regime with highly radiating X‐point: Physics and modelling

Senichenkov

Rozhansky

Shtyrkhunov

et al. 2022

Contributions to Plasma Physics

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“…While SOLPS-ITER simulations provide state-of-the-art predictions for the exhaust performances of the various divertor configurations, the predictions are sufficiently non-linear that is typically challenging to infer unambiguous causalities, dependencies, and conclusions about the obtained solutions. To address the need for a tractable and easily inferable model, several reduced models have been developed for predicting and analyzing the scrape-off layer (SOL) and divertor performance [11,12,13,14,15,16,17,18]. Most of these follow the Lengyel model [11], which uses simplifying assumptions about SOL transport to relate the SOL impurity density, upstream electron density, and the upstream SOL heat flux to the dissipated power and onset of detached conditions.…”

Section: Introductionmentioning

confidence: 99%

Parametric scaling of power exhaust in EU-DEMO alternative divertor simulations

Järvinen¹,

Aho-Mantila²,

Lunt³

et al. 2022

Preprint

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Investigations of parametric scaling of power exhaust in the alternative divertor configuration (ADC) SOLPS-ITER simulation database of the EU-DEMO are conducted and compared to predictions based on the Lengyel model. The Lengyel model overpredicts the necessary argon concentrations for LFS divertor detachment by about a factor of 5 -10 relative to the SOLPS-ITER simulations. Therefore, while the Lengyel model predicts that plasmas with accetable divertor heat loads in EU-DEMO would exceed the tolerable upstream impurity concentrations by a large margin, there are several SOLPS-ITER solutions within an acceptable operational space. The SOLPS-ITER simulations indicate that, unlike assumed by the standard Lengyel model, there are significant heat dissipation mechanisms other than argon radiation, such as cross-field transport, that reduce the role of argon radiation by a factor of 2 to 3. Furthermore, the Lengyel model assumes that the radiation front is powered by parallel heat conduction only, which tends to lead to a narrow radiation front as the radiative efficiency increases strongly with reducing thermal conductivity. As a result, the radiative volume and total impurity radiation are suppressed for a given impurity concentration. However, the SOLPS-ITER simulations indicate that other mechanisms, such as cross-field transport, can compete with parallel heat conduction within the radiative front and increase the radiative volume. Due to these findings, usage of the standard Lengyel model for analyzing scaling between divertor conditions and configurations for devices such as EU-DEMO is strongly discouraged.

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“…Therefore, it is necessary to reveal a scenario with the reasonable heat-flux on the target plates. The plasma detachment state is considered to be an efficient way to control the heat load on the target plate [1][2][3][4][5]. As a consequence, it is also necessary to understand fully the processes of plasma detachment in fusion devices.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation Study of the Magnetic Flux Tube Expansion on the Divertor Plasma Parameters by the LINDA Code

Islam

Nakashima

Ishiguro

et al. 2021

Plasma and Fusion Research

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In this research, we investigate the effect of magnetic flux tube expansion on the divertor plasma parameters by using the fluid code "LINDA". A comparison between the cylindrical flux tube (without the magnetic flux expansion) and the expansion magnetic flux tube has been undertaken. The aim of the study is to understand the impact of magnetic field expansion on the divertor physics by using the LINDA fluid code. The plasma density (n i ) is decreased and parallel velocity is increased (u i|| ) toward the target plate with the expansion of magnetic field lines near the target plate. The heat and particle fluxes are reduced significantly on the target plate in the case of the expansion mesh configuration. For the case of cylindrical mesh, advection becomes stronger with the decreasing distance from the target plate. In the case of expansion mesh, diffusion is stronger with the decreasing distance from the target plate. These outcomes clearly indicate the effect of the magnetic field structure on the divertor plasma parameters.

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Analytical calculations for impurity seeded partially detached divertor conditions

Cited by 61 publications

References 36 publications

Detached regime with highly radiating X‐point: Physics and modelling

Detached regime with highly radiating X‐point: Physics and modelling

Parametric scaling of power exhaust in EU-DEMO alternative divertor simulations

Numerical Simulation Study of the Magnetic Flux Tube Expansion on the Divertor Plasma Parameters by the LINDA Code

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