Haut PDF ELMs in High Recycling ITER Plasmas

ELMs in High Recycling ITER Plasmas

ELMs in High Recycling ITER Plasmas

Non-linear MHD code JOREK (www.jorek.eu) • JOREK code solves the (extended) MHD equations in 3D general tokamak geometry –Closed and open field lines, plasma wall interaction, conducting structures –Main applications: ELMs and disruptions

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Non-linear MHD Simulations of ELMs in a High Recycling Divertor

Non-linear MHD Simulations of ELMs in a High Recycling Divertor

The ITER H-mode equilibrium at 5.3T/15MA is characterized by a pedestal pressure of 126 kPa and a separatrix density of 0.32x10 20 m -3 (from IMAS #131025, [4]). A set of quasi-stationary states have been created with a varying gas injection rate. Fig.2 compares the ion and neutral density profiles and temperature profiles along the separatrix at the outer divertor. Included is a low recycling case with a zero reflection coefficient. With increasing gas injection, the density (and neutral density) at the divertor strongly increases, forming a thin layer with a width of about 3 cm. At the highest gas injection (C), the target temperature reduces to 6 eV compared to a temperature of 220 eV in the case (0) without recycling neutrals. In the high recycling cases (A-C) a constant background density of Neon at 5x10 17 m -3 is included. At the highest gas injection, Neon radiates 42 MW, the total radiation amounts to 70 MW with a total heating power of 110MW. In this case (C), the peak heat flux to the outer target is ~6 MW/m 2 .
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Cross-field plasma transport and main chamber recycling in diverted plasmas on Alcator C-Mod

Cross-field plasma transport and main chamber recycling in diverted plasmas on Alcator C-Mod

∇⋅ Γ + Γ ( 0 ) = 0 (3) where Γ and Γ 0 are the plasma and atomic neutral fluxes, n and n 0 are the corresponding densities and k ion is the ionization rate coefficient. Here, we assume that contributions from molecular species and volume recombination can be neglected in the region of interest. The SOL plasma can be decomposed into a series of adjacent flux tubes, each with length 2L , extending from one axisymmetric divertor surface to the other. For the purpose of illustration and the desire of simplicity, we consider the case when electron temperatures and densities are nearly constant along the flux tubes and the divertor surfaces are locally perpendicular to poloidal flux surfaces. Given that the main-chamber recycling condition is seen to persist in both sheath-limited and high recycling divertor regimes, the former restriction apparently does not exclude the essential physics. As a consequence of the orthogonal flux surface/wall geometry, the divertor plate becomes a flat, horizontal surface with no baffle structure. We may consider it as approximating a ‘virtual divertor surface’ formed by the divertor throat plus the baffle structure in the actual geometry of C-Mod.
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MHD-calibrated ELM model in simulations of ITER

MHD-calibrated ELM model in simulations of ITER

Self-consistent simulations of ITER are carried out using the JETTO predictive integrated modeling code [1] in which theory motivated models are used for the H-mode pedestal and for the stability conditions that lead to the ELM crashes. Each ELM crash results in a rapid loss of particles and energy from the edge of the plasma, which can reduce the average global energy content by 10-20%. In addition, ELMs play an essen- tial role in the control of the height of the pedestal in H-mode plasmas. A stability analysis is carried out using the stability analysis codes, HELENA and MISHKA, to confirm the stability criterion used to trigger ELM crashes in the JETTO code. Possible access to second stability of the ballooning mode is investigated using the HELENA and MISHKA stability analyses. With access to second stability, the edge pressure gradient can in- crease to a higher level, which results in a higher temperature at the top of the pedestal and, consequently, bet- ter plasma performance. The issue of ELM behavior and access to second stability is important for the success of ITER.
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Constraining the divertor heat width in ITER

Constraining the divertor heat width in ITER

5. Conclusions A model independent of measuring power widths λ r is developed which constrains ITER λ r based on global power balance, momentum conservation and recent improvements in understanding pedestal stability and sheath heat transmission. Experimental measurements suggest a separatrix to pedestal pressure ratio ~5% for ITER. Applying the simple model indicates a constraint that the allowed λ r ~ 10-30 mm for ITER if the divertor is in the high-recycling regime as expected (divertor T~5-20 eV). With a high-recycling divertor, a λ r ~1 mm would require a separatrix pressure approximately equal to the pressure at the top of the pedestal clearly in violation of the concept of a pedestal. A weaker constraint is also applied in the model that upstream separatrix pressure and T must simultaneously satisfy power balance. Even assuming large uncertainties in the model, it is not possible to satisfy power balance with a λ r < 4 mm even in the extreme case of divertor T > 100 eV.
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A coupling between cross-field density and temperature gradient scale lengths in high-recycling scrape-off layers

A coupling between cross-field density and temperature gradient scale lengths in high-recycling scrape-off layers

If one were allowed free choice of the energy and particle source distributions and the transport coefficients in numerical simulations of SOL plasmas then one could produce cross- field density and temperature profiles of arbitrary shape. However, in many SOL plasmas of interest, volumetric heat sources/sinks are small and the heat transport is dominated by a balance between anomalous cross-field transport and classical parallel electron conduction to the divertor target. This regime often exists in "high-recycling divertors" in which the electron- ion mean free path is much shorter than the distance between divertor surfaces along magnetic field lines.
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Radiation driven bifurcations in fusion plasmas

Radiation driven bifurcations in fusion plasmas

With respect to earlier papers on the radiative divertor, the present analytical work extends the results in two directions, first the location of the radiative front is introduced since the analytical work is complete and the profiles can be determined, second one can investigate the role of the upstream temperature and therefore introduce the cold SOL regime. Both aspects are shown to reduce the operating window and increase the con- straints on radiative divertor operation. An illustration of these features is obtained in the modified density regimes. Depending on the peak temperature of the impurity cool- ing rate, one finds that radiation either occurs in the linear (or sheath limited regime), terminating this regime at lower density, or in the high recycling regime where it favours a rapid drop of the divertor temperature but tends to govern a loss of the solution at large enough heat flux in the system. Analysing the benefit of radiation then crucially depends on the physics that take place when the solution is lost. The alternative could be either a transition of the form of a radiative density limit triggered by divertor conditions or a transition to plasma detachment and the continuation of divertor operation with completely modified particle recirculation. The investigation of plasma detachment thus appears as crucial in determining the benefit of impurity seeding and radiative divertor operation. This analysis is also most important to determine if the two terms of the al- ternative are effectively independent, or two successive steps of a single transient leading to plasma termination by a radiative collapse.
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Alcator C-Mod: research in support of ITER and steps beyond

Alcator C-Mod: research in support of ITER and steps beyond

2 I-mode, a naturally ELM-suppressed enhanced energy confinement regime, has been extended both to lower and higher magnetic fields. The window for entering and remaining in I-mode (between L- and H-mode) clearly widens at high field, important for consideration of extrapolation to ITER and high field reactors. Lower Hybrid frequency range microwaves have been used to modify the edge plasma, leading to increased pedestal pressure and improved confinement in H-modes. Studies of inter-ELM pedestal stability and fluctuations reveal an edge mode with many of the characteristics of Kinetic Ballooning, and direct correlation with pedestal saturation is directly observed. New tools are applied to yield detailed characterization of edge/SOL fluctuations: the mirror Langmuir probe, gives local measurements of Te, ne, p and their fluctuations, from a single probe, with msec time resolution, revealing unprecedented detail of the Quasi-Coherent Mode responsible for particle transport regulation in the EDA H-mode pedestal. Active MHD probing of the QCM, using a dedicated antenna (“shoelace”), shows that the mode can also be driven during ELM-free H-mode, where the QCM is not driven naturally by the free-energy in the plasma edge. Gyrokinetic simulations, which for the first time combine ion and electron scale turbulence, with realistic mass ratio, indicate that electron scale turbulence plays an important, even dominant role, in the core electron heat flux for L-mode plasmas, and may explain the under-prediction of experimentally observed e seen in the more standard, ion- scale simulations. A detailed series of studies of the phenomena across the change from Linear Ohmic Confinement (LOC, tEn) and Saturated Ohmic Confinement (SOC) reveals strong correlations between the LOC-SOC transition and changes in core intrinsic rotation, core temperature response to edge cooling perturbations, and up-down asymmetries in impurity densities at the edge plasma. Many
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Impact of divertor configuration on recycling neutral fluxes for ITER-like wall H-mode plasmas

Impact of divertor configuration on recycling neutral fluxes for ITER-like wall H-mode plasmas

Tiles 0 and 1 (see figure 1). The intensity increases during the configuration change by a factor of ten. 23 Below is a zoom of the blue frame of the upper figure. It can be seen that in-between ELMs the D  - 24

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Non-linear MHD simulations of QH-mode DIII-D plasmas and implications for ITER high Q scenarios

Non-linear MHD simulations of QH-mode DIII-D plasmas and implications for ITER high Q scenarios

[17] it was found that the resistive wall is not an essential ingredient to obtain a saturated kink-peeling mode (EHO). Kink-peeling modes which are unstable in the presence of an ideally conducting wall do saturate at a level consistent with experimentally observed amplitudes of the EHO. This indicates that the explanation proposed in [30], that the EHO is a saturated resistive wall mode at marginal stability, is not the only option to explain the occurrence of the EHO. The resistive wall is applied in one of the ITER simulations (see section 5) where the initial equilibrium is close to marginal stability. The time stepping is performed using the fully implicit Crank-Nicolson or Gear’s scheme, so that the size of time steps depends only on the time scale of the instabilities that are simulated. The implicit scheme results in a sparse system of equations, which is iteratively solved with the GMRES method. The diagonal block matrices corresponding to the individual toroidal harmonics are applied as an effective preconditioner, which are solved independently using the direct parallel sparse matrix solver PaStiX [23].
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Recycling and endogenous cycles

Recycling and endogenous cycles

Waste recycling activities concern growing industries for a large number of raw materials and these activities involve many kind of waste. For instance, European countries achieve record numbers in the recycling rate of glass (80%), of paper-cardboard (60%) and aluminium (75%). Nowadays, the world production of recycled aluminium is greater than the production of virgin aluminium. Economic literature analyses recycling from three theoretical points of view. First, recycling is integrated into the analysis of industrial organization; following the Alcoa case, studies have analyzed the erosion of monopoly power by competitive firms of recycled products (Grant, 1999). Second, natural resource economics studies point out the usefulness of recycling for economies facing a decrease in the availability of resources; recycling postpones the extraction of mining resources and reduces the intensity of forest exploitation (Dasgupta and Heal, 1979). Third, environmental economics analyses recycling as an instrument to reduce environmental externalities (Lusky, 1976). Yet, these studies do not analyze the consequences in terms of economic stability of the life cycle of the goods allowed by the recovery waste activity. This lacking literature justifies therefore our paper, which focuses on the consequence in terms of economic stability and of the occurrence of deterministic cycles of the recycling activity.
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Interactions plasmas-acier

Interactions plasmas-acier

III.3.3. Dépôt de couche mince organosiliciée par plasma basse pression Les couches minces, organiques ou inorganiques, obtenues par voie chimique en phase vapeur assistée par plasma (PECVD) à partir de précurseurs organosiliciés utilisés seuls ou en mélange avec de l'argon ou de l'oxygène, ont fait l'objet de multiples études depuis une trentaine d'années [58,62,64,72]. Les polymères déposés par cette technique (appelés polymères plasma) ont suscité un grand intérêt et conduit à de nombreux développements durant ces deux dernières décennies, dans des domaines aussi variés que l’optique [73-76], l'effet barrière au gaz [77,78], [79] les membranes, les couches de protection contre la corrosion [72,80]. Elles sont aussi intéressantes pour leur excellente résistance thermique [81,82] et leurs propriétés diélectriques et mécaniques [83,84]. La sureté, le coût relativement bas et les propriétés physique et chimique font partie des avantages des organosiloxanes par rapport aux autres monomères contenant du Si. Le tétraméthyledisiloxane est un des organosiloxanes les plus utilisés avec l'hexaméyhyldiloxane (HMDSO). Les dépôts par procédés plasmas à base de TMDSO font l’objet de nombreuses études incluant le diagnostic de la phase gaz qui permet de comprendre les mécanismes réactionnels impliqués plasma et la caractérisation du film [62,66].
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Dynamics of runaway electrons in tokamak plasmas

Dynamics of runaway electrons in tokamak plasmas

Abstract Runaway electrons can be generated in tokamak plasmas if the accelerating force from the toroidal electric field exceeds the collisional drag force owing to Coulomb collisions with the background plasma. In ITER, disruptions are expected to generate runaway electrons mainly through knock-on collisions (Hender et al 2007 Nucl. Fusion 47 S128 –202), where enough momentum can be transferred from existing runaways to slow electrons to transport the latter beyond a critical momentum, setting off an avalanche of runaway electrons. Since knock-on runaways are usually scattered off with a significant perpendicular component of the momentum with respect to the local magnetic field direction, these particles are highly magnetized. Consequently, the momentum dynamics require a full 3D kinetic description, since these electrons are highly sensitive to the magnetic non-uniformity of a toroidal configuration. For this purpose, a bounce-averaged knock-on source term is derived. The generation of runaway electrons from the combined effect of Dreicer mechanism and knock-on collision process is studied with the code LUKE, a solver of the 3D linearized bounce-averaged relativistic electron Fokker –Planck equation (Decker and Peysson 2004 DKE: a fast numerical solver for the 3D drift kinetic equation Report EUR-CEA-FC-1736, Euratom-CEA), through the calculation of the response of the electron distribution function to a constant parallel electric field. The model, which has been successfully benchmarked against the standard Dreicer runaway theory now describes the runaway generation by knock-on collisions as proposed by Rosenbluth (Rosenbluth and Putvinski 1997 Nucl. Fusion 37 1355 –62). This paper shows that the avalanche effect can be important even in non-disruptive scenarios. Runaway formation through knock-on collisions is found to be strongly reduced when taking place off the magnetic axis, since trapped electrons can not contribute to the runaway electron population. Finally, the relative importance of the avalanche mechanism is investigated as a function of the key parameters for runaway electron formation, namely the plasma temperature and the electric field strength. In agreement with theoretical predictions, the LUKE simulations show that in low temperature and electric field the knock-on collisions becomes the dominant source of runaway electrons and can play a significant role for runaway electron generation, including in non-disruptive tokamak scenarios.
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Plasmas dans l’eau et aux interfaces

Plasmas dans l’eau et aux interfaces

72 4.1.5 Initiation mechanisms of three modes 4.1.5.1 Mechanism of bubble formation As we have seen above in all three liquids with highly different dielectric permittivity, below the threshold voltage for discharge initiation a spherical low density cavity of 5 – 10 µm in size could be formed. As one can see in Figure 4.13 the maximal radius of the bubble varied between 13 µm for n-pentane at 10 kV and 30 µm for carbonated water at 3.5 kV. In all tested liquids formation of a gaseous cavity or a bubble was observed after the first incident HV pulse of positive polarity. However, as was already mentioned Section 3.5, the reflections from open end on the electrode side of the coaxial cable and from the zero output impedance of generator (output resistance of pulse generator is zero when HV diode is closed) produced a series of pulses of alternate polarity split by 260 ns. The typical voltage signal of 3.5 kV maximal amplitude obtained with the help of back current shunt (BCS) is shown in Figure 4.13. The dynamics of the bubble expansion shows that the bubble radius before arriving of the first reflected pulse varied between 9 µm and 13 µm depending on liquid (Figure 4.13). As one can see a spike-like increase in bubble radius occurred during the negative pulse in deionized water at 4 kV. The third pulse that had positive polarity and amplitude about 25% smaller comparing to initial pulse did not seem to produce strong effect on bubble size at 3.5 kV in deionized water, while at 4 kV the dynamics of bubble expansion was affected as can be seen from linear increase of the radius after the third pulse. In the case of ethanol at 4.5 kV and carbonated water at 3.5 kV the radius of the bubble has significantly increased likewise after the second and third pulses. In n-pentane the bubble expansion phase appeared to be about 4 times shorter than the collapse phase suggesting that reflected pulses possibly affected bubble dynamics.
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Self-organized turbulent transport in fusion plasmas

Self-organized turbulent transport in fusion plasmas

Dans le Chapitre 1, nous introduisons les ´el´ements de base des dispositifs de fu- sion magn´etique et le rˆ ole du transport turbulent dans l’op´eration et les performances des exp´eriences en cours ainsi que projet´ees dans ITER. Dans le Chapitre 2, les deux outils num´eriques, GYSELA et TOKAM2D, sont pr´esent´es. Les principaux choix pr´esidant aux diff´erences entre ces deux approches de la mod´elisation des plasmas sont mis en avant. Les forces et faiblesses de chacune des ap- proches sont analys´ees. Le mod`ele utilis´e dans le code cin´etique GYSELA est l’approche la plus directe. Elle est bas´ee sur un minimum d’hypoth`ese et vise ` a r´eduire au maxi- mum les param`etres libres pour se rapprocher des conditions de simulations ab-initio. Les limites de cette approche sont le coˆ ut de ces simulations, qui limitent en cons´equence les domaines ´etudi´es. Par ailleurs, l’identification et l’analyse des dynamiques non-lin´eaires qui conduisent ` a l’auto-organisation est particuli`erement difficile, rejoignant par certains aspects les conditions exp´erimentales o` u seule une information parcellaire est r´eellement accessible. Dans le cas de TOKAM2D, les attendus sont invers´es. Le mod`ele ne vise pas une simulation compl`ete, potentiellement r´ealiste du transport plasma dans les tokamaks. Au contraire, nous avons recherch´e la simplification maximale qui contienne encore les ´el´ements cruciaux de l’auto-organisation de la turbulence. Cette d´emarche nous permet d’aborder le probl`eme dans une plus grande g´en´eralit´e et de retrouver des probl`emes et des comportements g´en´eriques ` a d’autres champs de la physique comme l’oc´eanographie ou la physique des atmosph`eres.
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Recycling and sustainable development

Recycling and sustainable development

Evaluation environnementale des matériaux et des procédés de construction : application de l’analyse de cycle de vie à la construction d’un hall industriel.. Application: industrial hal[r]

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Study and modeling of the deuterium trapping in ITER relevant materials

Study and modeling of the deuterium trapping in ITER relevant materials

As explain before, MRE is used to determine detrapping energies from TDS measurements. However, it does not give any indication on the nature of the defects involved. A way to overpass this difficutly is to run the simulation with the DFT detrapping energies as Ahlgren et al. did for their model [136] using the DFT data from Heinola et al. [115] as inputs. The main issue is that the detrapping energies for any kind of defects are very close to each other which leads to broad experimental TDS spectra especially for PCW samples. So, MRE simulations used to determine detrapping energies will give the “mean” detrapping energies of all the defects that trap HIs. Looking at these “mean” detrapping energies recorded in table 2.3 , 3 values can be determined in case of undamaged W which are around 1.45 eV, 1.1 eV and 0.9 eV. If we compare these values to DFT values, it can be said that the 1.45 eV traps correspond to detrapping from vacancies type defect filled with 1 or 2 HIs (VH, VCH or VOH) or grain boundaries (if the migration depth is deeper than the typical grain size i.e. for high fluence). The detrapping energies 0.9 eV and the 1.1 eV could correspond to detrapping from vacancy with higher filling level (3-6), heavy impurities, grain boundaries or dislocation lines without kink/jog. According to DFT, the jogged dislocations and the dislocation loops have higher detrapping energies that range between 1.6 eV to 1.9 eV. No such detrapping energies are reported by MRE simulations for undamaged tungsten but they do in case of self-damaged damaged W: dislocation loops and jogged dislocations seem to trap D in the self-damaged W. Other traps with a detrapping energy around 2.1 eV can be determined in case of implantation of D at 500 K in SCW [43] or in any heavy ions or neutron damaged W. According to Ogorodnikova et al. [20], this detrapping energy is related to D trapped into void. To reach this conclusion, the adsorption model exposed by Gorodetsky et al. [139] has been used. This model considered that the detrapping energy of D with W in voids is the energy needed for an adsorbed D on W surface to go from the surface to the bulk.
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Contribution of kinetic electrons in Tokamak plasmas

Contribution of kinetic electrons in Tokamak plasmas

Résumé Les plasmas de fusion par connement magnétique sont le siège d'instabilités qui dévelop- pent des structures turbulentes d'échelles milli- à centi-métriques. Le transport qui en résulte contrôle le temps de connement de l'énergie et, in ne, les performances énergé- tiques. Dans les régimes de connement non améliorés, c'est une turbulence à l'échelle ionique qui domine ce transport. Cette turbulence est portée par les ions, mais également par une certaine classe d'électrons, ceux qui sont piégés dans les miroirs locaux du champ magnétique. Il est de fait important de prendre en compte leur dynamique, d'autant plus qu'ils sont également responsables du transport de matière. L'objectif de la thèse consiste à étudier l'impact des électrons d'une part, sur l'amortissement des "Geodesic Acoustic Modes" (GAM) d'une part, et sur la croissance linéaire des modes de turbulence "Ion Temperature Gradients" (ITG) et "Trapped Electron Modes" (TEM) d'autre part. Les GAMs sont des oscillations à la fréquence acoustique du potentiel électrique moyen sur les surfaces magnétiques. Ils interagissent de façon critique avec la micro-turbulence au travers notamment de leur couplage au mouvement des particules énergétiques du plasma. Les ITG et TEM représentent les 2 classes d'instabilités électrostatiques dom- inantes dans le c÷ur des plasmas de tokamak. Elles sont à ce titre supposées contrôler le transport turbulent de c÷ur. Cette étude est donc une étape préliminaire pour la prédiction du transport turbulent en prenant en compte l'inuence des électrons. Le cadre approprié pour décrire cette turbulence est la théorie dite "gyrocinétique", qui procède d'une réduction de l'espace des phases de 6 dimensions (6D) à 4D + 1 invariant par une moyenne sur le mouvement rapide cyclotronique. Le problème auto-consistant couple l'équation gyrocinétique pour chaque espèce (ions et électrons) aux équations de Maxwell. Le développement de ce modèle cinétique, construit comme une extension au- tonome du code Gysela dont la version de base donne une réponse adiabatique aux électrons, consiste à ajouter le traitement de la fonction de distribution des électrons. Leur prise en compte est coûteuse du point de vue des ressources numériques. Trois stratégies sont envisagées pour réduire ce coût: (i) considérer des "électrons lourds", (ii) ltrer les électrons et ne retenir que ceux qui sont piégés, et (iii) adapter les coordon- nées pour découpler les dynamiques parallèle (rapide) et transverse (lente) au champ magnétique.
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Considerations in the recycling of urban parking garages

Considerations in the recycling of urban parking garages

Because of the decreasing use of private automobiles in city centers and because of usual development pressures, some urban parking garages will become available fo[r]

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Multidimensional, multi-material and multiphysics modelling of Hydrogen transport in ITER

Multidimensional, multi-material and multiphysics modelling of Hydrogen transport in ITER

Rémi Delaporte-Mathurin, Jonathan Mougenot, Etienne Hodille, Y. Charles, Christian Grisolia. Mul- tidimensional, multi-material and multiphysics modelling of Hydrogen transport in ITER. [r]

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