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N. Fedorczak, C. Arnas, L. Cappelli, L. Colas, Y. Corre, et al.. Survey of tungsten gross erosion from main plasma facing components in WEST during a L-mode high fluence campaign. Nuclear Materials and Energy, 2024, 41 (4), pp.101758. ⟨10.1016/j.nme.2024.101758⟩. ⟨cea-04816563⟩ Plus de détails...
An initial high fluence campaign was performed in WEST, in 2023, on the newly installed actively cooled tungsten divertor composed of ITER-grade monoblocks. The campaign consisted in the repetition of a 60 s long Deuterium L-mode pulse in attached divertor conditions, cumulating over 10000s of plasma exposure. A maximum deuterium fluence of approximately 5 ⋅ 10 26 m -2 was reached in the outer strike point region, representative of a few high performance ITER pulses. Gross tungsten erosion inferred from visible spectroscopy shows that the most eroded plasma facing component is the inner divertor target with rates ten times larger than on the outer divertor target. The outer midplane tungsten bumpers, located a few centimeters from the plasma, show gross erosion rates two times lower than at the outer divertor. We conclude that the outer midplane bumpers have a negligible contribution to the long range tungsten migration and deposition onto the lower divertor. The cumulated gross erosion rate on the inner divertor translates in an effective gross erosion thickness of about 20 μm, while it is about 2 μm for the outer divertor. Strikingly, these orderings coincide with the thickness of deposits found locally on the divertor: the exposed surfaces of high field side monoblocks are covered with several tens of μm tungsten deposits, while on the lower field side, few μm thin tungsten deposits are only found on the magnetically shadowed parts of monoblocks. The strong impact of those deposits on WEST operation, namely perturbation of surface temperature measurement with infra-red thermography, and the emission of flakes causing radiative perturbation of the confined plasma, calls for anticipating similar issues in ITER. In particular, the start of research operation shall consider the definition of a divertor erosion budget in order to anticipate the formation of deleterious deposits.
N. Fedorczak, C. Arnas, L. Cappelli, L. Colas, Y. Corre, et al.. Survey of tungsten gross erosion from main plasma facing components in WEST during a L-mode high fluence campaign. Nuclear Materials and Energy, 2024, 41 (4), pp.101758. ⟨10.1016/j.nme.2024.101758⟩. ⟨cea-04816563⟩
Enrique de Dios Zapata Cornejo, David Zarzoso, S.D. Pinches, Andres Bustos, Alvaro Cappa, et al.. A novel unsupervised machine learning algorithm for automatic Alfvénic activity detection in the TJ-II stellarator. Nuclear Fusion, 2024, 64 (12), pp.126057. ⟨10.1088/1741-4326/ad85f4⟩. ⟨hal-04540368⟩ Plus de détails...
A novel sparse encoding algorithm is developed to detect and study plasma instabilities automatically. This algorithm, called Elastic Random Mode Decomposition, is applied to the Mirnov coil signals of a dataset of 1291 discharges of the TJ-II stellarator, enabling the identification of the Alfvénic activity. In the presented approach, each signal is encoded as a collection of basic waveforms called atoms, drawn from a signal’s dictionary. Then the modes are identified using clustering and correlations with other plasma signals. The performance of the proposed algorithm is dramatically increased by using elastic net regularization and taking advantage of GPU architectures, hence the signal size and the number of dictionary elements are no longer limiting factors for encoding complex signals. Once the modes are retrieved from the shots, they can be easily analyzed with standard clustering techniques, thereby describing the physical mode characteristics of this subset of TJ-II shots. The clustering features consider the relationship with the plasma current Ip, the diamagnetic energy W, and inverse squared root electronic density 1/√n, profiling different subtypes of Alfvénic activity. The proposed algorithm can potentially create large databases of labeled modes with unprecedented detail.
Enrique de Dios Zapata Cornejo, David Zarzoso, S.D. Pinches, Andres Bustos, Alvaro Cappa, et al.. A novel unsupervised machine learning algorithm for automatic Alfvénic activity detection in the TJ-II stellarator. Nuclear Fusion, 2024, 64 (12), pp.126057. ⟨10.1088/1741-4326/ad85f4⟩. ⟨hal-04540368⟩
Julian Wailliez, Paul Regazzi, Anniina Salonen, Paul G Chen, Marc Jaeger, et al.. Drop deformation in a planar elongational flow: impact of surfactant dynamics. Soft Matter, 2024, GDR MFA, 20 (44), pp.8793-8803. ⟨10.1039/D4SM00642A⟩. ⟨hal-04740537v2⟩ Plus de détails...
Drops in extensional flow undergo a deformation, which is primarily fixed by a balance between their surface tension and the viscous stress. This deformation, predicted and measured by Taylor on millimetric drops, is expected to be affected by the presence of surfactants but has never been measured systematically. We provide a controlled experiment allowing to measure this deformation as a function of the drop size and of the shear stress for different surfactants at varying concentrations. Our observation is that the deformation predicted by Taylor is recovered at zero and high surfactant concentration, whereas it is smaller at concentrations close to the critical micellar concentration. This is in contradiction with the existing analytical models. We develop a new analytical model, taking into account the surfactant dynamics. The model predicts a transition between a deformation similar to the one of a pure liquid and a smaller one. We show that the transition is driven by a parameter K_L , which compares adsorption and desorption dynamics. Finally, the concentration C* , at which we observe this transition in the extensional flow is in good agreement with the one predicted by independent measurement of K_L .
Julian Wailliez, Paul Regazzi, Anniina Salonen, Paul G Chen, Marc Jaeger, et al.. Drop deformation in a planar elongational flow: impact of surfactant dynamics. Soft Matter, 2024, GDR MFA, 20 (44), pp.8793-8803. ⟨10.1039/D4SM00642A⟩. ⟨hal-04740537v2⟩
Stefano Di Genova, Alberto Gallo, Luca Cappelli, Nicolas Fedorczak, Hugo Bufferand, et al.. Global analysis of tungsten migration in WEST discharges using numerical modelling. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad82f9⟩. ⟨hal-04739577⟩ Plus de détails...
Plasma discharges in the tungsten (W) Environment Steady-state Tokamak (WEST) are strongly impacted by W contamination. In WEST experiments, due to W contamination, the power radiated in the plasma (PRad) is on average, around 50% of the total power injected into the plasma (PTOT). Furthermore, this radiated power fraction (fRad) is almost insensitive to plasma conditions. The causes behind this experimental trend are not fully understood. In this contribution, a 3D numerical model is used to analyze the W migration in the WEST boundary plasma in different plasma scenarios. The WEST experimental database is sampled to obtain a scan of simulation input parameters. These parameters mimic the WEST plasma conditions over a chosen experimental campaign. The simulation results are compared to WEST diagnostics measurements (reflectometry, Langmuir probes, and visible spectroscopy) to verify that the simulated plasma conditions are representative of the WEST database. The W contamination trend is analysed: the W density (nW) strongly decreases when the radial distance between the separatrix and WEST antennas (Radial Outer Gap, ROG) increases. On the other hand, at a given ROG, nW increases proportionally with the power entering the scrape-off layer (PSOL). PRad is estimated with a simple 0D model. For a fixed ROG, fRad is not sensitive to plasma conditions. These trends are qualitatively and, at times, quantitatively comparable to what is observed in WEST experiments: the simulated trends are related to the poorly screened W influx caused by the erosion of the main chamber Plasma-Facing Components (PFCs). Thus, this numerical analysis suggests a possible interpretation of WEST experimental trends.
Stefano Di Genova, Alberto Gallo, Luca Cappelli, Nicolas Fedorczak, Hugo Bufferand, et al.. Global analysis of tungsten migration in WEST discharges using numerical modelling. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad82f9⟩. ⟨hal-04739577⟩
M. Scotto D’abusco, I. Kudashev, G. Giorgiani, Anna Glasser, F. Schwander, et al.. First integrated core-edge fluid simulation of ITER’s Limiter-Divertor transition with SolEdge-HDG. Nuclear Materials and Energy, 2024, pp.101750. ⟨10.1016/j.nme.2024.101750⟩. ⟨hal-04720290⟩ Plus de détails...
This work explores the Limiter-Divertor transition (L-D) during the current ramp-up of ITER's Q=10 baseline plasma scenario at various central line-integrated density n_(li) values. The analysis, based on transport simulations performed with the latest version of SoleEdge-HDG, focuses on the time evolution of heat and ion particle fluxes, revealing regions of elevated temperature on the inner wall and plasma-facing components (PFCs) despite moderate loads.The investigation also delves into the effects of perpendicular convection flux terms on density build-up, comparing different formulations and their interplay with auxiliary heating sources. Furthermore, the paper shows the impact of taking into account the evolution of the parallel neutral momentum on plasma and neutral density at the targets in the context of an ITER steady-state scenario.
M. Scotto D’abusco, I. Kudashev, G. Giorgiani, Anna Glasser, F. Schwander, et al.. First integrated core-edge fluid simulation of ITER’s Limiter-Divertor transition with SolEdge-HDG. Nuclear Materials and Energy, 2024, pp.101750. ⟨10.1016/j.nme.2024.101750⟩. ⟨hal-04720290⟩
H Betar, David Zarzoso, Jacobo Varela, Diego Del-Castillo-Negrete, Luis Garcia, et al.. Transport and losses of energetic particles in tokamaks in the presence of Alfvén activity using the new full orbit TAPaS code coupled to FAR3d. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad7c66⟩. ⟨hal-04541528v2⟩ Plus de détails...
Recent developments and tools integrated into the TAPaS code are presented, enabling realistic scenario simulations of particle dynamics within experimental tokamak magnetic equilibria. In particular, the enhanced capabilities of TAPaS enable seamless coupling with external simulations, provided the metric and equilibrium magnetic field of the external code are known. Coupling TAPaS with the gyro-fluid code FAR3d, the transport and losses of energetic particles in the presence Alfvén eigenmodes (AEs) in DIII-D plasma discharge #159243 were investigated. Detailed analyses of prompt losses with and without collisions were performed. Then, further analysis was performed in the presence of electromagnetic perturbations resulting from AEs activity. The results indicate that, for the energies and the initial conditions considered here, the presence of AEs enhances the particle losses.
H Betar, David Zarzoso, Jacobo Varela, Diego Del-Castillo-Negrete, Luis Garcia, et al.. Transport and losses of energetic particles in tokamaks in the presence of Alfvén activity using the new full orbit TAPaS code coupled to FAR3d. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad7c66⟩. ⟨hal-04541528v2⟩
Q. Mao, Umberto d'Ortona, J. Favier. Hydrodynamic coupling of a cilia–mucus system in Herschel–Bulkley flows. Journal of Fluid Mechanics, 2024, 994, pp.A8. ⟨10.1017/jfm.2024.600⟩. ⟨hal-04735292⟩ Plus de détails...
The yield stress and shear thinning properties of mucus are identified as critical for ciliary coordination and mucus transport in human airways. We use here numerical simulations to explore the hydrodynamic coupling of cilia and mucus with these two properties using the Herschel–Bulkley model, in a lattice Boltzmann solver for the fluid flow. Three mucus flow regimes, i.e. a poorly organized regime, a swirly regime, and a fully unidirectional regime, are observed and analysed by parametric studies. We systematically investigate the effects of ciliary density, interaction length, Bingham number and flow index on the mucus flow regime formation. The underlying mechanism of the regime formation is analysed in detail by examining the variation of two physical quantities (polarization and integral length) and the evolution of the flow velocity, viscosity and shear-rate fields. Mucus viscosity is found to be the dominant parameter influencing the regime formation when enhancing the yield stress and shear thinning properties. The present model is able to reproduce the solid body rotation observed in experiments (Loiseau et al. , Nat. Phys. , vol. 16, 2020, pp. 1158–1164). A more precise prediction can be achieved by incorporating non-Newtonian properties into the modelling of mucus as proposed by Gsell et al. ( Sci. Rep. , vol. 10, 2020, 8405).
Q. Mao, Umberto d'Ortona, J. Favier. Hydrodynamic coupling of a cilia–mucus system in Herschel–Bulkley flows. Journal of Fluid Mechanics, 2024, 994, pp.A8. ⟨10.1017/jfm.2024.600⟩. ⟨hal-04735292⟩
Adil Mouahid, Magalie Claeys-Bruno, Sébastien Clercq. A New Methodology Based on Experimental Design and Sovová’s Broken and Intact Cells Model for the Prediction of Supercritical CO2 Extraction Kinetics. Processes, 2024, 12 (9), pp.1865. ⟨10.3390/pr12091865⟩. ⟨hal-04791947⟩ Plus de détails...
Nowadays, supercritical CO2 extraction is highly regarded in industry, and several studies dealing with scale-up calculations aim to facilitate the transition from small scale to large scale. To complete this transition, it would be interesting to be able to predict supercritical CO2 extraction kinetics, which is the aim of this work. A new methodology based on the association of Sovová’s broken and intact cell model and response surface methodology was developed to predict SC-CO2 extraction kinetics from different biomass (Argan kernels, evening primrose, Punica granatum, Camellia sinensis, and dry paprika) at different operating conditions (200–700 bar, 40–60 °C, 0.14–10 kg/h) inside an operating domain. The absolute average relative deviations between the experimental and predicted data ranged from 1.86 to 29.03%, showing satisfactory reliability of this new methodology.
Adil Mouahid, Magalie Claeys-Bruno, Sébastien Clercq. A New Methodology Based on Experimental Design and Sovová’s Broken and Intact Cells Model for the Prediction of Supercritical CO2 Extraction Kinetics. Processes, 2024, 12 (9), pp.1865. ⟨10.3390/pr12091865⟩. ⟨hal-04791947⟩
L Cappelli, N Fedorczak, E Serre. Semi-analytical modelling of prompt redeposition in a steady-state plasma. Nuclear Fusion, 2024, 64 (10), pp.106028. ⟨10.1088/1741-4326/ad6c5e⟩. ⟨hal-04685227⟩ Plus de détails...
A steady-state, 1D semi-analytical model for prompt redeposition based on the separation between redeposition caused by the electric field in the sheath and redeposition related to gyromotion is here described. The model allows for the estimation of not only the fraction of promptly redeposited flux but also the energy and angular distribution of the non-promptly redeposited population, along with their average charge state. Thus, the temperature and mean parallel-to-B velocity of the non-promptly redeposited flux are also available. The semi-analytical model was validated against equivalent Monte Carlo simulations across a broad range of input parameters. In this paper the eroded material under exam was tungsten (W) for which the code demonstrated consistent agreement with respect to numerical results, within its defined validity limits. The model can theoretically provide a solution for any material, temperature and electron density profile in the sheath, monotonic potential drop profile, and sputtered particles energy and angular distribution at the wall. As such, this code emerges as a potential tool for addressing the boundary redeposition phenomenon in fluid impurity transport simulations.
L Cappelli, N Fedorczak, E Serre. Semi-analytical modelling of prompt redeposition in a steady-state plasma. Nuclear Fusion, 2024, 64 (10), pp.106028. ⟨10.1088/1741-4326/ad6c5e⟩. ⟨hal-04685227⟩
R Varennes, Guilhem Dif-Pradalier, P Ghendrih, V Grandgirard, O Panico, et al.. Synergy of turbulent momentum drive and magnetic braking. Plasma Physics and Controlled Fusion, 2024, 66 (10), pp.105008. ⟨10.1088/1361-6587/ad705c⟩. ⟨hal-03631224⟩ Plus de détails...
Abstract Relaxations of localized over-density in a plane transverse to the magnetic field are numerically investigated under the effect of drift-wave and interchange drives in SOL conditions. Such a controlled departure from thermodynamic equilibrium allows the investigation of fundamental processes at play in cross-field transport. Interchange instabilities generate ballistic outward radial flux with low amplitude zonal flow patterns, whereas drift-wave instabilities result in symmetric radial flux with large amplitude zonal flow patterns. When both instabilities are considered, the combined effects tend to favor drift-waves, leading to a weaker outward flux with larger zonal flow patterns.
R Varennes, Guilhem Dif-Pradalier, P Ghendrih, V Grandgirard, O Panico, et al.. Synergy of turbulent momentum drive and magnetic braking. Plasma Physics and Controlled Fusion, 2024, 66 (10), pp.105008. ⟨10.1088/1361-6587/ad705c⟩. ⟨hal-03631224⟩
