Giorgio Giorgiani, H. Bufferand, G. Ciraolo, P. Ghendrih, Frédéric Schwander, et al.. A hybrid discontinuous Galerkin method for tokamak edge plasma simulations in global realistic geometry. Journal of Computational Physics, Elsevier, 2018, 374, pp.515-532. 〈hal-01946999〉 Plus de détails...
Progressing toward more accurate and more efficient numerical codes for the simulation of transport and turbulence in the edge plasma of tokamaks, we propose in this work a new hybrid discontinuous Galerkin solver. Based on 2D advection-diffusion conservation equations for the ion density and the particle flux in the direction parallel to the magnetic field, the code simulates plasma transport in the poloidal section of tokamaks, including the open field lines of the Scrape-off Layer (SOL) and the closed field lines of the core region. The spatial discretization is based on a high-order hybrid DG scheme on unstructured meshes, which provides an arbitrary high-order accuracy while reducing considerably the number of coupled degrees of freedom with a local condensation process. A discontinuity sensor is employed to identify critical elements and regularize the solution with the introduction of artificial diffusion. Based on a finite-element discretization, not constrained by a flux-aligned mesh, the code is able to describe plasma facing components of any complex shape using Bohm boundary conditions and to simulate the plasma in versatile magnetic equilibria, possibly extended up to the center. Numerical tests using a manufactured solution show appropriate convergence orders when varying independently the number of elements or the degree of interpolation. Validation is performed by benchmarking the code with the well-referenced edge transport code SOLEDGE2D (Bufferand et al., 2013, 2015 [1,2]) in the WEST geometry. Final numerical experiments show the capacity of the code to deal with low-diffusion solutions.
Giorgio Giorgiani, H. Bufferand, G. Ciraolo, P. Ghendrih, Frédéric Schwander, et al.. A hybrid discontinuous Galerkin method for tokamak edge plasma simulations in global realistic geometry. Journal of Computational Physics, Elsevier, 2018, 374, pp.515-532. 〈hal-01946999〉
Camille Baudoin, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, et al.. Drift driven cross-field transport and scrape-off layer width in the limit of low anomalous transport. Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (10), pp.105007. 〈hal-01947253〉 Plus de détails...
The impact of the del B-drift in the cross-field transport and its effect on the density and power scrape-off layer (SOL) width in the limit of low anomalous transport is studied with the fluid code SolEdge2D. In the first part of the work, the simulations are run with an isothermal reduced fluid model. It is found that a del B-drift dominated regime is reached in all geometries studied (JET-like, ASDEX-like and circular analytic geometries), and that the transition toward this regime comes along with the apparition of supersonic shocks, and a complex parallel equilibrium. The parametric dependencies of the SOL width in this regime are investigated, and the temperature and the poloidal magnetic field are found to be the principal parameters governing the evolution of the SOL width. In the second part of this paper, the impact of additional physics is studied (inclusion of the centrifugal drift, self-consistent variation of temperature and the treatment of the neutral species). The addition of centrifugal drift and neutral species are shown to play a role in the establishment of the parallel equilibrium, impacting the SOL's width, although the role of the centrifugal drift is limited to a low diffusion level. Finally, the numerical results are compared with the estimate of the Goldston's heuristic drift based model (HD-model), the starting point of our study, and which has shown good agreement with experimental scaling laws. We find that the particles SOL widths in the del B-drift dominated regime are at least two times smaller than the estimate of the HD-model. Moreover, in the parametric dependencies proposed by the HD-model, the dependency with B-pol is retrieved, but not the one on T.
Camille Baudoin, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, et al.. Drift driven cross-field transport and scrape-off layer width in the limit of low anomalous transport. Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (10), pp.105007. 〈hal-01947253〉
H. Bufferand, G. Ciraolo, P. Di Cintio, N. Fedorczak, Ph. Ghendrih, et al.. Non-local heat flux application for scrape-off layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.563-569. 〈hal-01947239〉 Plus de détails...
The non-local expression proposed by Luciani-Mora-Virmont is implemented in a one dimensional fluid model for the scrape-off layer. Analytical solutions for heat equation are discussed as well as the impact of sheath boundary conditions on the continuity of the temperature profile. The non-local heat flux is compared to the Spitzer-Harm heat flux for different collisionality.
H. Bufferand, G. Ciraolo, P. Di Cintio, N. Fedorczak, Ph. Ghendrih, et al.. Non-local heat flux application for scrape-off layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.563-569. 〈hal-01947239〉
L. Valade, A. Ekedahl, P. Ghendrih, Y. Sarazin, Y. Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.465-470. 〈hal-01947214〉 Plus de détails...
Hotspot generation by lower-hybrid (LH) launchers is found to be governed by a resonance in the plasma electric field response to the external drive. The kinetic analysis in 1D-1V in the parallel direction allows one to compute the amplification effect for small amplitude of the external drive. The resonant Lorentzian response distorts the distribution function. An island structure is formed in the suprathermal part at the phase velocity of the external electrostatic drive. The non-linear features enhance the plasma response, driving overlap effects between multiple waves at rather low amplitude. The onset of a plateau in the distribution function, with extent reaching one thermal velocity, is already obtained when the standard overlap condition is achieved. The sensitivity of the resonance to plasma parameters and large variation of the amplification magnitude can compensate the fast radial decay of the small-scale features generated by the LH launchers, which are responsible for the interaction with the cold electrons. This mechanism can trigger hotspot generation further in the scrape-off layer than otherwise expected.
L. Valade, A. Ekedahl, P. Ghendrih, Y. Sarazin, Y. Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.465-470. 〈hal-01947214〉
Guido Ciraolo, Hugo Bufferand, Pierfrancesco Di Cintio, Philippe Ghendrih, Stefano Lepri, et al.. Fluid and kinetic modelling for non-local heat transport in magnetic fusion devices. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.457-464. 〈hal-01947205〉 Plus de détails...
In order to improve the presently used ad hoc flux limiter treatment of parallel heat flux transport in edge plasma fluid codes, here, we consider a generalized version of the Fourier law implementing a non-local kernel for the heat flux computation. The Bohm boundary condition at the wall is recovered, introducing a volumetric loss term representing the contribution of suprathermal particles to the energy out flux. As expected, this contribution is negligible in the strongly collisional regime, while it becomes more and more dominant for marginally and low-collisional regimes. In the second part of the paper, we consider a kinetic approach where collisions are considered using the multi-particle collision algorithm. Kinetic simulation results at medium and low collisionality are also reported.
Guido Ciraolo, Hugo Bufferand, Pierfrancesco Di Cintio, Philippe Ghendrih, Stefano Lepri, et al.. Fluid and kinetic modelling for non-local heat transport in magnetic fusion devices. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.457-464. 〈hal-01947205〉
Serafina Baschetti, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Optimization of turbulence reduced model free parameters based on L-mode experiments and 2D transport simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.511-517. 〈hal-01947233〉 Plus de détails...
In this paper, a -E transport model is presented as a turbulence reduction tool for a typical ohmic L-mode discharge plasma in a divertor-configurated tokamak. Taking a Tokamak a configuration variable (TCV) study case, a feedback loop procedure is performed using the SolEdge2D code to acquire plasma diffusivity at the outer mid-plane. The -E model is calibrated through its free parameters with the aim of recovering the diffusivity calculated in the feedback procedure. Finally, it is shown that the model can self-consistently calculate diffusivity in the whole domain, recovering the poloidal asymmetries due to interchange instabilities.
Serafina Baschetti, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Optimization of turbulence reduced model free parameters based on L-mode experiments and 2D transport simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.511-517. 〈hal-01947233〉
Nicolas Nace, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Impact of safety factor and magnetic shear profiles on edge turbulence in circular limited geometry. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.497-504. 〈hal-01947228〉 Plus de détails...
The impact of magnetic configuration on edge turbulence properties in circular limiter geometry is investigated using TOKAM3X, a three-dimensional (3D), first-principle, fluid code for edge plasma. The theoretical spatial tilting of magnetic shear on turbulence fluctuations is recovered. Magnetic shear is found to generate or enhance poloidal high/low field sides (HFS/LFS) and up/down asymmetries. A simulation mimicking the impact of an X-point on circular limiter geometry leads to the formation of two transport barriers that are stable in time, thus leading to the improvement of core particle confinement and to reduction of radial turbulent transport. The magnetic shear, which also strongly enhances the E x B shear, is responsible for the barrier formation.
Nicolas Nace, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Impact of safety factor and magnetic shear profiles on edge turbulence in circular limited geometry. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.497-504. 〈hal-01947228〉
M. Valentinuzzi, Giorgio Giorgiani, Y. Marandet, H. Bufferand, G. Ciraolo, et al.. Fluid description of neutral particles in divertor regimes in WEST. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.710-717. 〈hal-01947244〉 Plus de détails...
A new neutral fluid code has been developed as a necessary step towards a hybrid fluid/kinetic neutral model, to be used in ITER or DEMO simulations, where part of the divertor will be very collisional for neutrals. The neutral fluid code, which is able to handle complex geometries in view of the coupling to Soledge2D, is tested on plasma backgrounds obtained by Soledge2D-Eirene in WEST geometry, for different divertor regimes, and is found to be in fair agreement with the kinetic Monte Carlo solver Eirene. The differences are due to the simplifications introduced in the fluid model and to the fact that a fluid description is not fully valid in these cases.
M. Valentinuzzi, Giorgio Giorgiani, Y. Marandet, H. Bufferand, G. Ciraolo, et al.. Fluid description of neutral particles in divertor regimes in WEST. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.710-717. 〈hal-01947244〉
D.-M. Fan, Y. Marandet, P. Tamain, H. Bufferand, G. Ciraolo, et al.. Self-consistent coupling of the three-dimensional fluid turbulence code TOKAM3X and the kinetic neutrals code EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.490-496. 〈hal-01947222〉 Plus de détails...
The three-dimensional (3D) turbulence code TOKAM3X-EIRENE, coupling the 3D non-isothermal version of TOKAM3X to the EIRENE Monte Carlo solver has been developed with the ability to simulate self-consistently the interactions between large-scale flows and turbulence both in limited and diverted plasmas, including recycling. This is especially important for diverted plasmas, where neutrals play a key role and where the recycling source is strongly dominant. The code package relies on the same interface as the Soledge2D-EIRENE code, which retains state-of-the-art plasma-wall interaction, as well as atomic and molecular physics. In this paper, we present the first results obtained in WEST divertor geometry, in laminar mode, with the aim of verifying the new code package. The divertor density regimes are recovered, and the code results are shown to be consistent with the results of the two-point model, thus opening the way for turbulent simulations.
D.-M. Fan, Y. Marandet, P. Tamain, H. Bufferand, G. Ciraolo, et al.. Self-consistent coupling of the three-dimensional fluid turbulence code TOKAM3X and the kinetic neutrals code EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.490-496. 〈hal-01947222〉
G Gallo, N. Fedorczak, S Elmore, M Maurizio, H Reimerdes, et al.. Impact of the plasma geometry on divertor power exhaust: experimental evidence from TCV and simulations with SolEdge2D and TOKAM3X. Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (1), pp.014007. 〈10.1088/1361-6587/aa857b〉. 〈hal-01713287〉 Plus de détails...
A deep understanding of plasma transport at the edge of magnetically confined fusion plasmas is needed for the handling and control of heat loads on the machine first wall. Experimental observations collected on a number of tokamaks over the last three decades taught us that heat flux profiles at the divertor targets of X-point configurations can be parametrized by using two scale lengths for the scrape-off layer (SOL) transport, separately characterizing the main SOL (lambda(q)) and the divertor SOL (S-q). In this work we challenge the current interpretation of these two scale lengths as well as their dependence on plasma parameters by studying the effect of divertor geometry modifications on heat exhaust in the Tokamak a Configuration Variable. In particular, a significant broadening of the heat flux profiles at the outer divertor target is diagnosed while increasing the length of the outer divertor leg in lower single null, Ohmic, L-mode discharges. Efforts to reproduce this experimental finding with both diffusive (SolEdge2D-EIRENE) and turbulent (TOKAM3X) modelling tools confirm the validity of a diffusive approach for simulating heat flux profiles in more traditional, short leg, configurations while highlighting the need of a turbulent description for modified, long leg, ones in which strongly asymmetric divertor perpendicular transport develops.
G Gallo, N. Fedorczak, S Elmore, M Maurizio, H Reimerdes, et al.. Impact of the plasma geometry on divertor power exhaust: experimental evidence from TCV and simulations with SolEdge2D and TOKAM3X. Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (1), pp.014007. 〈10.1088/1361-6587/aa857b〉. 〈hal-01713287〉
G. Ciraolo, H. Bufferand, J. Bucalossi, Ph. Ghendrih, P. Tamain, et al.. H-mode WEST tungsten divertor operation: deuterium and nitrogen seeded simulations with SOLEDGE2D-EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.187 - 192. 〈10.1016/j.nme.2016.12.025〉. 〈hal-01702237〉 Plus de détails...
Simulations of WEST H-mode divertor scenarios have been performed with SOLEDGE2D-EIRENE edge plasma transport code, both for pure deuterium and nitrogen seeded discharge. In the pure deuterium case, a target heat flux of 8 MW/m2 is reached, but misalignment between heat and the particle outflux yields 50 eV plasma temperature at the target plates. With nitrogen seeding, the heat and particle outflux are observed to be aligned so that lower plasma temperatures at the target plates are achieved together with the required high heat fluxes. This change in heat and particle outflux alignment is analysed with respect to the role of divertor geometry and the impact of vertical vs horizontal target plates on neutrals spreading.
G. Ciraolo, H. Bufferand, J. Bucalossi, Ph. Ghendrih, P. Tamain, et al.. H-mode WEST tungsten divertor operation: deuterium and nitrogen seeded simulations with SOLEDGE2D-EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.187 - 192. 〈10.1016/j.nme.2016.12.025〉. 〈hal-01702237〉
Y. Marandet, H. Bufferand, N. Nace, M. Valentinuzzi, G. Ciraolo, et al.. Towards a consistent modelling of plasma edge turbulence in mean field transport codes: Focus on sputtering and plasma fluctuations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.931 - 934. 〈10.1016/j.nme.2017.02.007〉. 〈hal-01702229〉 Plus de détails...
Transport codes are the main workhorses for global edge studies and modern divertor design. These tools do not resolve turbulent fluctuations responsible for the bulk of cross-field transport in the Scrape-off Layer (SOL), and solve mean field equations instead. Turbulent fluxes are modelled by diffusive transport along the gradients of the mean fields. Improvements of this description, on the basis of approaches developed in computational fluid dynamics are discussed, broadening the outlook given in Bufferand et al. (2016) [10]. This contribution focuses on additional closure issues related to non-linearities in sources/sinks from plasma-wall interactions, here sputtered fluxes from the plasma facing components. “Fluctuation dressed” sputtering yields Yeff are introduced and calculated from turbulence simulations. Properly taking fluctuations into account is shown to lead to higher sputtering at sub-threshold energies compared to mean field predictions. As a first step towards an implementation in a transport code, the possibility of parametrizing Yeff in terms of the mean fields is tentatively investigated.
Y. Marandet, H. Bufferand, N. Nace, M. Valentinuzzi, G. Ciraolo, et al.. Towards a consistent modelling of plasma edge turbulence in mean field transport codes: Focus on sputtering and plasma fluctuations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.931 - 934. 〈10.1016/j.nme.2017.02.007〉. 〈hal-01702229〉
P. Tamain, C. Colin, L. Colas, C. Baudoin, G. Ciraolo, et al.. Numerical analysis of the impact of an RF sheath on the Scrape-Off Layer in 2D and 3D turbulence simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.1171 - 1177. 〈10.1016/j.nme.2016.12.022〉. 〈hal-01702267〉 Plus de détails...
Motivated by Radio Frequency (RF) heating studies, the response of the plasma of tokamaks to the presence of a locally polarized limiter is studied. In a first part, we use the TOKAM3X 3D global edge turbulence code to analyse the impact of such biasing in a realistic geometry. Key features of experimental observations are qualitatively recovered, especially the extension of a potential and density perturbation on long, but finite, distances along connected field lines. The perturbation is also found to extend in the transverse direction. Both observations demonstrate the influence of perpendicular current loops on the plasma confirming the need for an accurate description in reduced models. In a second part, we use the TOKAM2D slab turbulence code to determine the validity of using a transverse Ohm's law for this purpose. Results indicate that a local Ohm's law with a constant and uniform perpendicular resistivity appears at least as an oversimplified description of perpendicular charge transport in a turbulent Scrape-Off Layer.
P. Tamain, C. Colin, L. Colas, C. Baudoin, G. Ciraolo, et al.. Numerical analysis of the impact of an RF sheath on the Scrape-Off Layer in 2D and 3D turbulence simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.1171 - 1177. 〈10.1016/j.nme.2016.12.022〉. 〈hal-01702267〉
Davide Galassi, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Flux expansion effect on turbulent transport in 3D global simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.953 - 958. 〈10.1016/j.nme.2017.01.008〉. 〈hal-01702255〉 Plus de détails...
The flux expansion effect on the Scrape-Off Layer equilibrium is inspected through TOKAM3X 3D turbulence simulations. Three magnetic equilibria with analytically controlled flux expansion are built, representing respectively a positive, a null and a negative Shafranov shift. Turbulent E × B fluxes across flux surfaces show similar amplitudes and poloidal distributions in all cases. The ballooning nature of the interchange instability is recovered, with an enhancement of turbulence in the vicinity of the limiter, probably due to a Kelvin–Helmoltz instability. Interestingly, the poloidally averaged density decay length is found to be shorter almost by a factor 2 in the case of flux surfaces compressed at the low-field side midplane, with respect to the opposite case, indicating the presence of unfavorable conditions for the turbulent transport. The difference in the magnetic field line shape is pointed out as a mechanism which affects the turbulent transport across the flux surfaces. Indeed the unstable region has a larger parallel extension when flux expansion in the low-field side is larger. Moreover, the configuration with a lower magnetic shear at the low-field side midplane shows a more unstable behavior. The role of this parameter in turbulence stabilization is qualitatively evaluated. The difference in the distribution of transport along the parallel direction is shown to affect also the parallel flows, which are analyzed for the three proposed cases.
Davide Galassi, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Flux expansion effect on turbulent transport in 3D global simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.953 - 958. 〈10.1016/j.nme.2017.01.008〉. 〈hal-01702255〉
H. Bufferand, C. Baudoin, J. Bucalossi, G. Ciraolo, J. Denis, et al.. Implementation of drift velocities and currents in SOLEDGE2D–EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.852 - 857. 〈10.1016/j.nme.2016.11.031〉. 〈hal-01702275〉 Plus de détails...
In order to improve cross-field transport description, drifts and currents have been implemented in SOLEDGE2D–EIRENE. The derivation of an equation for the electric potential is recalled. The resolution of current equation is tested in a simple slab case. WEST divertor simulations in forward-B and reverse-B fields are also discussed. A significant increase of ExB shear is observed in the forward-B configuration that could explain a favorable L-H transition in this case.
H. Bufferand, C. Baudoin, J. Bucalossi, G. Ciraolo, J. Denis, et al.. Implementation of drift velocities and currents in SOLEDGE2D–EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.852 - 857. 〈10.1016/j.nme.2016.11.031〉. 〈hal-01702275〉
Davide Galassi, P. Tamain, H. Bufferand, Guido Ciraolo, Ph. Ghendrih, et al.. Drive of parallel flows by turbulence and large-scale E × B transverse transport in divertor geometry. Nuclear Fusion, IOP Publishing, 2017, 57 (3), pp.036029. 〈10.1088/1741-4326/aa5332〉. 〈hal-01592945〉 Plus de détails...
The poloidal asymmetries of parallel flows in edge plasmas are investigated by the 3D fluid turbulence code TOKAM3X. A diverted COMPASS-like magnetic equilibrium is used for the simulations. The measurements and simulations of parallel Mach numbers are compared, and exhibit good qualitative agreement. Small-scale turbulent transport is observed to dominate near the low field side midplane, even though it co-exists with significant large-scale cross-field fluxes. Despite the turbulent nature of the plasma in the divertor region, simulations show the low effectiveness of turbulence for the cross-field transport towards the private flux region. Nevertheless, a complex pattern of fluxes associated with the average field components are found to cross the separatrix in the divertor region. Large-scale and small-scale turbulent E x B transport, along with the del B drift, drive the asymmetries in parallel flows. A semian-alytical model based on mass and parallel momentum balances allows the poloidal drift effects on the asymmetry pattern to be evaluated. As in the experiments, a reversed B-T simulation provides a way of self-consistently separating the effects of turbulent transport and large-scale flows, which must be reversed for a reversed field. The large-scale contribution is found to be responsible for typically 50% of the effect on the Mach number, evaluated at the top of the machine. The presented picture shows the complex interplay between drifts and turbulence, underlining the necessity of a global approach to edge plasma modelling, including a self-consistent description of the turbulence.
Davide Galassi, P. Tamain, H. Bufferand, Guido Ciraolo, Ph. Ghendrih, et al.. Drive of parallel flows by turbulence and large-scale E × B transverse transport in divertor geometry. Nuclear Fusion, IOP Publishing, 2017, 57 (3), pp.036029. 〈10.1088/1741-4326/aa5332〉. 〈hal-01592945〉
Hugo Bufferand, G. Ciraolo, P Di Cintio, N Fedorczak, Ph Ghendrih, et al.. Nonlocal heat flux application for Scrape-off Layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, In press. 〈hal-01655295〉 Plus de détails...
The nonlocal expression proposed by Luciani-Mora-Virmont is implemented into a 1D fluid model for the scrape-off layer. Analytic solutions for heat equation are discussed as well as the impact of sheath boundary conditions on the continuity of the temperature profile. The nonlocal heat flux is compared to Spitzer-Härm heat flux for different collisionality.
Hugo Bufferand, G. Ciraolo, P Di Cintio, N Fedorczak, Ph Ghendrih, et al.. Nonlocal heat flux application for Scrape-off Layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, In press. 〈hal-01655295〉
X. Litaudon, S. Abduallev, M. Abhangi, P. Abreu, M. Afzal, et al.. Overview of the JET results in support to ITER. Nuclear Fusion, IOP Publishing, 2017, 57 (10), pp.102001. 〈hal-01660974〉 Plus de détails...
The 2014-2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER is supported by first principle modelling. ITER relevant disruption experiments and first principle modelling are reported with a set of three disruption mitigation valves mimicking the ITER setup. Insights of the L-H power threshold in Deuterium and Hydrogen are given, stressing the importance of the magnetic configurations and the recent measurements of fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal confinement provide new information to elucidate the importance of the first wall material on the fusion performance. H-mode plasmas at ITER triangularity (H = 1 at beta(N) similar to 1.8 and n/n(GW) similar to 0.6) have been sustained at 2 MA during 5 s. The ITER neutronics codes have been validated on high performance experiments. Prospects for the coming D-T campaign and 14 MeV neutron calibration strategy are reviewed.
X. Litaudon, S. Abduallev, M. Abhangi, P. Abreu, M. Afzal, et al.. Overview of the JET results in support to ITER. Nuclear Fusion, IOP Publishing, 2017, 57 (10), pp.102001. 〈hal-01660974〉
O. Kazakov, J. Ongena, E. Lerche, M. Mantsinen, D. Van eester, et al.. Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating. Nature Physics, Nature Publishing Group, 2017, 13, pp.973-978. 〈10.1038/NPHYS4167〉. 〈cea-01898634〉 Plus de détails...
We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed ‘three-ion’ scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of $^3$He ions to high energies in dedicated hydrogen–deuterium mixtures. Simultaneously, effective plasma heating is observed, as a result of the slowing-down of the fast $^3$He ions. The developed technique is not only limited to laboratory plasmas, but can also be applied to explain observations of energetic ions in space-plasma environments, in particular, $^3$He-rich solar flares.
O. Kazakov, J. Ongena, E. Lerche, M. Mantsinen, D. Van eester, et al.. Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating. Nature Physics, Nature Publishing Group, 2017, 13, pp.973-978. 〈10.1038/NPHYS4167〉. 〈cea-01898634〉
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Davide Galassi, et al.. The TOKAM3X code for edge turbulence fluid simulations of tokamak plasmas in versatile magnetic geometries. Journal of Computational Physics, Elsevier, 2016, 321, pp.606-623. 〈10.1016/j.jcp.2016.05.038〉. 〈hal-01461797〉 Plus de détails...
The new code TOKAM3X simulates plasma turbulence in full torus geometry including the open field lines of the Scrape-off Layer (SOL) and the edge closed field lines region in the vicinity of the separatrix. Based on drift-reduced Braginskii equations, TOKAM3X is able to simulate both limited and diverted plasmas. Turbulence is flux driven by incoming particles from the core plasma and no scale separation between the equilibrium and the fluctuations is assumed so that interactions between large scale flows and turbulence are consistently treated. Based on a domain decomposition, specific numerical schemes are proposed using conservative finite-differences associated to a semi-implicit time advancement. The process computation is multi-threaded and based on MPI and OpenMP libraries. In this paper, fluid model equations are presented together with the proposed numerical methods. The code is verified using the manufactured solution technique and validated through documented simple experiments. Finally, first simulations of edge plasma turbulence in X-point geometry are also introduced in a JET geometry. (C) 2016 Elsevier Inc. All rights reserved.
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Davide Galassi, et al.. The TOKAM3X code for edge turbulence fluid simulations of tokamak plasmas in versatile magnetic geometries. Journal of Computational Physics, Elsevier, 2016, 321, pp.606-623. 〈10.1016/j.jcp.2016.05.038〉. 〈hal-01461797〉
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Yannick Marandet, J. Bucalossi, et al.. Interchange Turbulence Model for the Edge Plasma in SOLEDGE2D-EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.555-562. 〈10.1002/ctpp.201610033〉. 〈hal-01455239〉 Plus de détails...
Cross-field transport in edge tokamak plasmas is known to be dominated by turbulent transport. A dedicated effort has been made to simulate this turbulent transport from first principle models but the numerical cost to run these simulations on the ITER scale remains prohibitive. Edge plasma transport study relies mostly nowadays on so-called transport codes where the turbulent transport is taken into account using effective ad-hoc diffusion coeffecients. In this contribution, we propose to introduce a transport equation for the turbulence intensity in SOLEDGE2D-EIRENE to describe the interchange turbulence properties. Going beyond the empirical diffusive model, this system automatically generates profiles for the turbulent transport and hence reduces the number of degrees of freedom for edge plasma transport codes. We draw inspiration from the k-epsilon model widely used in the neutral fluid community. ((c) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Yannick Marandet, J. Bucalossi, et al.. Interchange Turbulence Model for the Edge Plasma in SOLEDGE2D-EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.555-562. 〈10.1002/ctpp.201610033〉. 〈hal-01455239〉
Patrick Tamain, Hugo Bufferand, L. Carbajal, Yannick Marandet, C. Baudoin, et al.. Interplay between Plasma Turbulence and Particle Injection in 3D Global Simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.569-574. 〈10.1002/ctpp.201610063〉. 〈hal-01455242〉 Plus de détails...
The impact of a 3D localized particle source on the edge plasma in 3D global turbulence simulations is investigated using the TOKAM3X fluid code. Results apply to advanced fueling methods such as Supersonic Molecular Beam Injection (SMBI) or pellets injection. The fueling source is imposed as a volumetric particle source in the simulations so that the physics leading to the ionization of particles and its localization are not taken into account. As already observed in experiments, the localized particle source strongly perturbs both turbulence and the large scale organization of the edge plasma. The localized increase of the pressure generated by the source drives sonic parallel flows in the plasma, leading to a poloidal redistribution of the particles on the time scale of the source duration. However, the particle deposition also drives localized transverse pressure gradients which impacts the stability of the plasma with respect to interchange processes. The resulting radial transport occurs on a sufficiently fast time scale to compete with the parallel redistribution of particles, leading to immediate radial losses of a significant proportion of the injected particles. Low Field Side (LFS) and High Field Side (HFS) injections exhibit different dynamics due to their interaction with curvature. In particular, HFS particle deposition drives an inward flux leading to differences in the particle deposition efficiency (higher for HFS than LFS). These results demonstrate the importance of taking into account plasma transport in a self-consistent manner when investigating fueling methods. ((c) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Patrick Tamain, Hugo Bufferand, L. Carbajal, Yannick Marandet, C. Baudoin, et al.. Interplay between Plasma Turbulence and Particle Injection in 3D Global Simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.569-574. 〈10.1002/ctpp.201610063〉. 〈hal-01455242〉
R. Futtersack, C. Colin, Patrick Tamain, Guido Ciraolo, Philippe Ghendrih, et al.. First Principle Modelling of Interplay between Langmuir Probes and Plasma Turbulence. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.575-580. 〈10.1002/ctpp.201610038〉. 〈hal-01455240〉 Plus de détails...
The interplay between Langmuir probes (LP) and Scrape-Off-Layer plasma turbulence is numerically investigated with the TOKAM2D and TOKAM3X fluid codes. The LP is modelled by biasing a part of the target plates surface; we then study its impact on the turbulent transport 1) in presence of electron temperature fluctuations and 2) with a complete description of the parallel dynamics. We find that a biased probe can disturb local plasma parameters as well as turbulent transport in its vicinity, by polarizing the connected flux tube and thus driving a strong ExB vortex. Moreover, electron temperature fluctuations are found to account significantly those of floating potential, but with a limited impact on flux measurements depending on the probe's exact geometry. The 3D study of the problem shows the attenuation, but the persistency, of these perturbations induced by the presence of the LP. ((c) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
R. Futtersack, C. Colin, Patrick Tamain, Guido Ciraolo, Philippe Ghendrih, et al.. First Principle Modelling of Interplay between Langmuir Probes and Plasma Turbulence. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.575-580. 〈10.1002/ctpp.201610038〉. 〈hal-01455240〉
Luc Di Gallo, Cédric Reux, Frédéric Imbeaux, Jean-François Artaud, Michal Owsiak, et al.. Coupling between a multi-physics workflow engine and an optimization framework. Computer Physics Communications, Elsevier, 2016, 200, pp.76-86. 〈10.1016/j.cpc.2015.11.002〉. 〈hal-01461783〉 Plus de détails...
A generic coupling method between a multi-physics workflow engine and an optimization framework is presented in this paper. The coupling architecture has been developed in order to preserve the integrity of the two frameworks. The objective is to provide the possibility to replace a framework, a workflow or an optimizer by another one without changing the whole coupling procedure or modifying the main content in each framework. The coupling is achieved by using a socket-based communication library for exchanging data between the two frameworks. Among a number of algorithms provided by optimization frameworks, Genetic Algorithms (GAs) have demonstrated their efficiency on single and multiple criteria optimization. Additionally to their robustness, GAs can handle non-valid data which may appear during the optimization. Consequently GAs work on most general cases. A parallelized framework has been developed to reduce the time spent for optimizations and evaluation of large samples. A test has shown a good scaling efficiency of this parallelized framework. This coupling method has been applied to the case of SYCOMORE (System COde for MOdeling tokamak REactor) which is a system code developed in form of a modular workflow for designing magnetic fusion reactors. The coupling of SYCOMORE with the optimization platform URANIE enables design optimization along various figures of merit and constraints. (C) 2015 EURATOM. Published by Elsevier B.V. All rights reserved.
Luc Di Gallo, Cédric Reux, Frédéric Imbeaux, Jean-François Artaud, Michal Owsiak, et al.. Coupling between a multi-physics workflow engine and an optimization framework. Computer Physics Communications, Elsevier, 2016, 200, pp.76-86. 〈10.1016/j.cpc.2015.11.002〉. 〈hal-01461783〉
J. Denis, B. Pégourié, J. Bucalossi, Hugo Bufferand, Guido Ciraolo, et al.. Wall surface temperature calculation in the SolEdge2D-EIRENE transport code. Physica Scripta, IOP Publishing, 2016, T167, 〈10.1088/0031-8949/T167/1/014073〉. 〈hal-01459103〉 Plus de détails...
A thermal wall model is developed for the SolEdge2D-EIRENE edge transport code for calculating the surface temperature of the actively-cooled vessel components in interaction with the plasma. This is a first step towards a self-consistent evaluation of the recycling of particles, which depends on the wall surface temperature. The proposed thermal model is built to match both steady-state temperature and time constant of actively-cooled plasma facing components. A benchmark between this model and the Finite Element Modelling code CAST3M is performed in the case of an ITER-like monoblock. An example of application is presented for a SolEdge2D-EIRENE simulation of a medium-power discharge in the WEST tokamak, showing the steady-state wall temperature distribution and the temperature cycling due to an imposed Edge Localised Mode-like event.
J. Denis, B. Pégourié, J. Bucalossi, Hugo Bufferand, Guido Ciraolo, et al.. Wall surface temperature calculation in the SolEdge2D-EIRENE transport code. Physica Scripta, IOP Publishing, 2016, T167, 〈10.1088/0031-8949/T167/1/014073〉. 〈hal-01459103〉
Cédric Reux, Luc Di Gallo, Frédéric Imbeaux, Jean-François Artaud, P. Bernardi, et al.. DEMO reactor design using the new modular system code SYCOMORE. Nuclear Fusion, IOP Publishing, 2015, 55 (7), 〈10.1088/0029-5515/55/7/073011〉. 〈hal-01462144〉 Plus de détails...
A demonstration power plant (DEMO) will be the next step for fusion energy following ITER. Some of the key design questions can be addressed by simulations using system codes. System codes aim to model the whole plant with all its subsystems and identify the impact of their interactions on the design choices. The SYCOMORE code is a modular system code developed to address key questions relevant to tokamak fusion reactor design. SYCOMORE is being developed within the European Integrated Tokamak Modelling framework and provides a global view (technology and physics) of the plant. It includes modules to address plasma physics, divertor physics, breeding blankets, shield design, magnet design and the power balance of plant. The code is coupled to an optimization framework which allows one to specify figures of merit and constraints to obtain optimized designs. Examples of pulsed and steady-state DEMO designs obtained using SYCOMORE are presented. Sensitivity to design assumptions is also studied, showing that the operational domain around working points can be narrow for some cases.
Cédric Reux, Luc Di Gallo, Frédéric Imbeaux, Jean-François Artaud, P. Bernardi, et al.. DEMO reactor design using the new modular system code SYCOMORE. Nuclear Fusion, IOP Publishing, 2015, 55 (7), 〈10.1088/0029-5515/55/7/073011〉. 〈hal-01462144〉
Patrick Tamain, Philippe Ghendrih, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, et al.. Multi-scale self-organisation of edge plasma turbulent transport in 3D global simulations. Plasma Physics and Controlled Fusion, IOP Publishing, 2015, 57 (5), pp.054014. 〈10.1088/0741-3335/57/5/054014〉. 〈hal-01299732〉 Plus de détails...
The 3D global edge turbulence code TOKAM3X is used to study the properties of edge particle turbulent transport in circular limited plasmas, including both closed and open flux surfaces. Turbulence is driven by an incoming particle flux from the core plasma and no scale separation between the equilibrium and the fluctuations is assumed. Simulations show the existence of a complex self-organization of turbulence transport coupling scales ranging from a few Larmor radii up to the machine scale. Particle transport is largely dominated by small scale turbulence with fluctuations forming quasi field-aligned filaments. Radial particle transport is intermittent and associated with the propagation of coherent structures on long distances via avalanches. Long range correlations are also found in the poloidal and toroidal direction. The statistical properties of fluctuations vary with the radial and poloidal directions, with larger fluctuation levels and intermittency found in the outboard scrape-off layer (SOL). Radial turbulent transport is strongly ballooned, with 90% of the flux at the separatrix flowing through the low-field side. One of the main consequences is the existence of quasi-sonic asymmetric parallel flows driving a net rotation of the plasma. Simulations also show the spontaneous onset of an intermittent E × B rotation characterized by a larger shear at the separatrix. Strong correlation is found between the turbulent particle flux and the E × B flow shear in a phenomenology reminiscent of H-mode physics. The poloidal position of the limiter is a key player in the observed dynamics.
Patrick Tamain, Philippe Ghendrih, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, et al.. Multi-scale self-organisation of edge plasma turbulent transport in 3D global simulations. Plasma Physics and Controlled Fusion, IOP Publishing, 2015, 57 (5), pp.054014. 〈10.1088/0741-3335/57/5/054014〉. 〈hal-01299732〉
Clothilde Colin, Patrick Tamain, Frederic Schwander, Eric Serre, Hugo Bufferand, et al.. Impact of the plasma-wall contact position on edge turbulent transport and poloidal asymmetries in 3D global turbulence simulations. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.654-658. 〈10.1016/j.jnucmat.2015.01.019〉. 〈hal-01225200〉 Plus de détails...
A 3D global turbulence fluid code, TOKAM3X is used to investigate the effect of the limiter position on the edge plasma parallel flows and density profiles. Six configurations with different poloidal contact points in the machine are considered. For each one, asymmetric quasi-sonic parallel flows are found, owing to the ballooning of radial turbulent transport around the LFS mid-plane. In spite of the relative simplicity of the model used (isothermal, sheat-limited, no recycling), simulations exhibit trends in-line with experimental findings. Reversal of the flows is found when the limiter is moved from −30° under to 30° above the outboard mid-plane. The SOL width varies with the poloidal location and depends notably on the poloidal position of the limiter. Turbulence itself is shown to be impacted by the position of the limiter, radial transport appearing less ballooned with a LFS limiter than with a HFS.
Clothilde Colin, Patrick Tamain, Frederic Schwander, Eric Serre, Hugo Bufferand, et al.. Impact of the plasma-wall contact position on edge turbulent transport and poloidal asymmetries in 3D global turbulence simulations. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.654-658. 〈10.1016/j.jnucmat.2015.01.019〉. 〈hal-01225200〉
Hugo Bufferand, Guido Ciraolo, Yannick Marandet, Jérome Bucalossi, Philippe Ghendrih, et al.. Numerical modelling for divertor design of the WEST device with a focus on plasma–wall interactions. Nuclear Fusion, IOP Publishing, 2015, 55 (5), pp.053025. 〈hal-01225195〉 Plus de détails...
In the perspective of operating tungsten monoblocks in WEST, the ongoing major upgrade of the Tore Supra tokamak, a dedicated modelling effort has been carried out to simulate the interaction between the edge plasma and the tungsten wall. A new transport code, SolEdge2D–EIRENE, has been developed with the ability to simulate the plasma up to the first wall. This is especially important for steady state operation, where thermal loads on all the plasma facing components, even remote from the plasma, are of interest. Moreover, main chamber tungsten sources are thought to dominate the contamination of the plasma core. We present here in particular new developments aimed at improving the description of the interface between the plasma and the wall, namely a way to treat sheath physics in a more faithful way using the output of 1D particle in cell simulations. Moreover, different models for prompt redeposition have been implemented and are compared. The latter is shown to play an important role in the balance between divertor and main chamber sources.
Hugo Bufferand, Guido Ciraolo, Yannick Marandet, Jérome Bucalossi, Philippe Ghendrih, et al.. Numerical modelling for divertor design of the WEST device with a focus on plasma–wall interactions. Nuclear Fusion, IOP Publishing, 2015, 55 (5), pp.053025. 〈hal-01225195〉
R. Leybros, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Investigation of drift velocity effects on the EDGE and SOL transport. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.489-492. 〈10.1016/j.jnucmat.2014.10.079〉. 〈hal-01225211〉 Plus de détails...
To understand the mechanisms behind poloidal asymmetries of the transport in the edge and SOL plasma, it is important to take into account drift velocity in the transport model. We investigate the effects of an imposed radial electric field on the plasma equilibrium in the transport code SOLEDGE2D. In the edge, we show an important modification of the flow pattern due to poloidal E × B drift velocity. The drift velocity generates asymmetry of the density through the Pfirsch–Schluter flows which creates an important parallel rotation through the viscous balance. In comparison to heat load imbalance studies in the SOL of divertor tokamak, a strong link between the amplitude of the radial electric field and the heat load imbalance in the SOL of limiter tokamak has been highlighted using different amplitude of the imposed radial electric field.
R. Leybros, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Investigation of drift velocity effects on the EDGE and SOL transport. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.489-492. 〈10.1016/j.jnucmat.2014.10.079〉. 〈hal-01225211〉
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, P. Genesio, et al.. Comparison on heat flux deposition between carbon and tungsten wall – Investigations on energy recycling. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.420-423. 〈10.1016/j.jnucmat.2014.09.061〉. 〈hal-01225205〉 Plus de détails...
The influence of the plasma facing components material on the scrape-off layer plasma is investigated. In particular, the energy recycling is found to be more pronounced for tungsten wall compared with carbon wall. Edge plasma simulations performed with the transport code SOLEDGE2D-EIRENE show that this enhanced energy recycling in the tungsten case leads to an increase of the scrape-off layer temperature. Moreover, the energy recycling depends on the ion angle of incidence with the wall. A PIC code has been used to model the ion acceleration in the magnetic pre-sheath and determine the later angle of incidence. These simulations show that ions mostly impact the wall with rather shallow incident angles leading to a further increase of the energy recycling.
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, P. Genesio, et al.. Comparison on heat flux deposition between carbon and tungsten wall – Investigations on energy recycling. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.420-423. 〈10.1016/j.jnucmat.2014.09.061〉. 〈hal-01225205〉
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak ă with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. 〈10.1016/j.jcp.2014.05.025〉. 〈hal-01464707〉 Plus de détails...
To properly address turbulent transport in the edge plasma region of a ă tokamak, it is mandatory to describe the particle and heat outflow on ă wall components, using an accurate representation of the wall geometry. ă This is challenging for many plasma transport codes, which use a ă structured mesh with one coordinate aligned with magnetic surfaces. We ă propose here a penalization technique that allows modeling of particle ă and heat transport using such structured mesh, while also accounting for ă geometrically complex plasma-facing components. Solid obstacles are ă considered as particle and momentum sinks whereas ionic and electronic ă temperature gradients are imposed on both sides of the obstacles along ă the magnetic field direction using delta functions (Dirac). Solutions ă exhibit plasma velocities (M = 1) and temperatures fluxes at the ă plasma-wall boundaries that match with boundary conditions usually ă implemented in fluid codes. Grid convergence and error estimates are ă found to be in agreement with theoretical results obtained for neutral ă fluid conservation equations. The capability of the penalization ă technique is illustrated by introducing the non-collisional plasma ă region expected by the kinetic theory in the immediate vicinity of the ă interface, that is impossible when considering fluid boundary ă conditions. Axisymmetric numerical simulations show the efficiency of ă the method to investigate the large-scale transport at the plasma edge ă including the separatrix and in realistic complex geometries while ă keeping a simple structured grid. (C) 2014 Elsevier Inc. All rights ă reserved.
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak ă with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. 〈10.1016/j.jcp.2014.05.025〉. 〈hal-01464707〉
Hugo Bufferand, Guido Ciraolo, Guilhem Dif-Pradalier, Philippe Ghendrih, Patrick Tamain, et al.. Magnetic geometry and particle source drive of supersonic divertor regimes. Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56 (122001), 〈10.1088/0741-3335/56/12/122001〉. 〈hal-01225185〉 Plus de détails...
We present a comprehensive picture of the mechanisms driving the transition from subsonic to supersonic flows in tokamak plasmas. We demonstrate that supersonic parallel flows into the divertor volume are ubiquitous at low density and governed by the divertor magnetic geometry. As the density is increased, subsonic divertor plasmas are recovered. On detachment, we show the change in particle source can also drive the transition to a supersonic regime. The comprehensive theoretical analysis is completed by simulations in ITER geometry. Such results are essential in assessing the divertor performance and when interpreting measurements and experimental evidence. The generation of large-scale flows in laboratory plasma is a highly non-linear problem. In a standard fashion it is considered that the flows remain subsonic away from the wall, the occurrence of supersonic flows being singular. We show here that the geometrical features of key configurations for fusion plasma can lead to supersonic flows.
Hugo Bufferand, Guido Ciraolo, Guilhem Dif-Pradalier, Philippe Ghendrih, Patrick Tamain, et al.. Magnetic geometry and particle source drive of supersonic divertor regimes. Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56 (122001), 〈10.1088/0741-3335/56/12/122001〉. 〈hal-01225185〉
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Density regimes and heat flux deposition in the WEST shallow divertor configuration. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.378-382. 〈10.1002/ctpp.201410026〉. 〈hal-01053281〉 Plus de détails...
To support ITER divertor design, the WEST project on Tore Supra aims at studying high heat fluxes on tungsten monoblock during long pulses. In that persective, a particular attention is paid to simulate the edge plasma interaction with complex PFCs using the transport code SOLEDGE2D-EIRENE. The plasma response to a heating and puffing scenario is described as well as the so-called divertor density regimes, characterizing the operational domain of the WEST divertor. These results are compared for two different magnetic configurations: a semi-open double null divertor with the X-point away from the target plates and a shallow divertor configuration with the X-point close to the targets.
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Density regimes and heat flux deposition in the WEST shallow divertor configuration. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.378-382. 〈10.1002/ctpp.201410026〉. 〈hal-01053281〉
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Philippe Ghendrih, et al.. 3D properties of edge turbulent transport in full-torus simulations and their impact on poloidal asymmetries. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.555-559. 〈10.1002/ctpp.201410017〉. 〈hal-01053290〉 Plus de détails...
The 3D fluid turbulence code TOKAM3X is used to investigate the 3D properties of edge turbulent transport and their impact on poloidal asymmetries. Simulations are run in circular limited plasmas in a domain covering both closed and open flux surfaces. Turbulence characteristics exhibit large inhomogeneities both in the radial and poloidal directions reminiscent of experimental observations. The low field side mid-plane in particular is found to be locally more fluctuating and intermittent than the rest of the Scrape-Off-Layer (SOL). As a consequence of this asymmetry, radial turbulent transport, that represents 80 to 90% of the total radial flux, is strongly ballooned, with 75% of the flux flowing through LFS. The equilibrium of the edge plasma is impacted by this asymmetry through the existence of large amplitude asymmetric parallel flows as well as through the development of poloidally asymmetric radial decay lengths making it impossible to define a single SOL width.
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Philippe Ghendrih, et al.. 3D properties of edge turbulent transport in full-torus simulations and their impact on poloidal asymmetries. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.555-559. 〈10.1002/ctpp.201410017〉. 〈hal-01053290〉
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. 〈hal-01087225〉 Plus de détails...
To properly address turbulent transport in the edge plasma region of a tokamak, it is mandatory to describe the particle and heat outflow on wall components, using an accurate representation of the wall geometry. This is challenging for many plasma transport codes, which use a structured mesh with one coordinate aligned with magnetic surfaces. We propose here a penalization technique that allows modelingof particle and heat transport using such structured mesh, while also accounting for geometrically complex plasma-facing components. Solid obstacles are considered as particle and momentum sinks whereas ionic and electronic temperature gradients are imposed on both sides of the obstacles along the magnetic field direction using delta functions (Dirac). Solutions exhibit plasma velocities (M=1) and temperatures fluxes at the plasma–wall boundaries that match with boundary conditions usually implemented in fluid codes. Grid convergence and error estimates are found to be in agreement with theoretical results obtained for neutral fluid conservation equations. The capability of the penalization technique is illustrated by introducing the non-collisional plasma region expected by the kinetic theory in the immediate vicinity of the interface, that is impossible when considering fluid boundary conditions. Axisymmetric numerical simulations show the efficiency of the method to investigate the large-scale transport at the plasma edge including the separatrix and in realistic complex geometries while keeping a simple structured grid.
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. 〈hal-01087225〉
Guido Ciraolo, Hugo Bufferand, Philippe Ghendrih, Patrick Tamain, Jérome Bucalossi, et al.. Investigation of edge and SOL particle flux patterns in high density regimes using SOLEDGE2D-EIRENE code. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.432-436. 〈10.1002/ctpp.201410018〉. 〈hal-01050505〉 Plus de détails...
We present numerical simulations of plasma transport obtained with the SOLEDGE2D code coupled to the EIRENE Montecarlo code for neutrals. We consider a double null magnetic configuration in a WEST geometry. Density and temperatures parallel profiles in the SOL domain are presented as well as Mach profile. We detail how using the penalization technique we are able to model plasma transport up to the first wall having access to energy and particle fluxes on the entire chamber wall. Moreover, we present the computed 2D contour map of the plasma mach number and of the magnitude of the ionisation source term in the whole poloidal section, emphasizing how complex and realistic geometries can be handled thanks to the penalization technique.
Guido Ciraolo, Hugo Bufferand, Philippe Ghendrih, Patrick Tamain, Jérome Bucalossi, et al.. Investigation of edge and SOL particle flux patterns in high density regimes using SOLEDGE2D-EIRENE code. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.432-436. 〈10.1002/ctpp.201410018〉. 〈hal-01050505〉
Elena Floriani, Guido Ciraolo, Philippe Ghendrih, Yanick Sarazin, Ricardo Lima. Self-regulation of turbulence bursts and transport barriers. Plasma Physics and Controlled Fusion, IOP Publishing, 2013, 55 (9), pp.095012. 〈10.1088/0741-3335/55/9/095012〉. 〈hal-00733279〉 Plus de détails...
The interplay between turbulent bursts and transport barriers is analyzed with a simplified model of interchange turbulence in the Scrape-Off Layer of magnetically confined plasmas. The turbulent bursts spread into the transport barriers, and, depending on the competing magnitude of the burst and stopping capability of the barrier can burn through. Two models of transport barriers are presented, a hard barrier where all turbulent modes are stable in a prescribed region and a soft barrier with external plasma biasing. This process can be modeled on the basis of competing stochastic processes. For classes of probability density function of these processes one can predict the heavy tail properties of the bursts downstream from the barrier, either exponential for a leaky barrier, or with power laws, for a tight barrier. The intrinsic probing of the transport barriers by the turbulent bursts thus gives access to properties of the transport barriers. The main stochastic variables of the two models addressed here are the barrier width and the spreading distance of the turbulent bursts within the barrier together with their level of correlation. One finds that in the case of a barrier located in the Scrape-Off-Layer, the stochastic model predicts a leaky barrier with an exponential probability density function of escaping turbulent bursts in agreement with the simulation data.
Elena Floriani, Guido Ciraolo, Philippe Ghendrih, Yanick Sarazin, Ricardo Lima. Self-regulation of turbulence bursts and transport barriers. Plasma Physics and Controlled Fusion, IOP Publishing, 2013, 55 (9), pp.095012. 〈10.1088/0741-3335/55/9/095012〉. 〈hal-00733279〉
Philippe Ghendrih, Thomas Auphan, B. Bensiali, Marco Bilanceri, K. Bodi, et al.. Divertor imbalance and divertor density regimes for ballooned cross-field turbulence. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.S368-S371. 〈http://www.sciencedirect.com/science/article/pii/S0022311513000780〉. 〈10.1016/j.jnucmat.2013.01.070〉. 〈hal-00920748〉 Plus de détails...
The ballooned nature of cross-field transport is shown to govern the steady state divertor imbalance of the energy flux leading to a factor 10 between the low field side and high field energy flux. An even stronger ratio is found for the divertor temperatures. Conversely the particle flux is expected to be a factor 10 larger on the high field side than on the low field side. The transition to detachment, close to divertor thermal collapse, exhibits several constraints to maintain steady state solutions. These constraints, related in particular to a large drop of the divertor density upon detachment, are shown to strongly correlate the pressure and particle flux variation along the field line and consequently the various loss channels. This delicate balance between different mechanisms is a possible understanding of the difficulty reported in detached plasma operation and simulation.
Philippe Ghendrih, Thomas Auphan, B. Bensiali, Marco Bilanceri, K. Bodi, et al.. Divertor imbalance and divertor density regimes for ballooned cross-field turbulence. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.S368-S371. 〈http://www.sciencedirect.com/science/article/pii/S0022311513000780〉. 〈10.1016/j.jnucmat.2013.01.070〉. 〈hal-00920748〉
Bouchra Bensiali, Kowsik Bodi, Guido Ciraolo, Philippe Ghendrih, Jacques Liandrat. Comparison of different interpolation operators including nonlinear ă subdivision schemes in the simulation of particle trajectories. Journal of Computational Physics, Elsevier, 2013, 236, pp.346-366. 〈10.1016/j.jcp.2012.11.025〉. 〈hal-01464719〉 Plus de détails...
In this work, we compare different interpolation operators in the ă context of particle tracking with an emphasis on situations involving ă velocity field with steep gradients. Since, in this case, most classical ă methods give rise to the Gibbs phenomenon (generation of oscillations ă near discontinuities), we present new methods for particle tracking ă based on subdivision schemes and especially on the Piecewise Parabolic ă Harmonic (PPH) scheme which has shown its advantage in image processing ă in presence of strong contrasts. First an analytic univariate case with ă a discontinuous velocity field is considered in order to highlight the ă effect of the Gibbs phenomenon on trajectory calculation. Theoretical ă results are provided. Then, we show, regardless of the interpolation ă method, the need to use a conservative approach when integrating a ă conservative problem with a velocity field deriving from a potential. ă Finally, the PPH scheme is applied in a more realistic case of a ă time-dependent potential encountered in the edge turbulence of ă magnetically confined plasmas, to compare the propagation of density ă structures (turbulence bursts) with the dynamics of test particles. This ă study highlights the difference between particle transport and density ă transport in turbulent fields. (C) 2012 Elsevier Inc. All rights ă reserved.
Bouchra Bensiali, Kowsik Bodi, Guido Ciraolo, Philippe Ghendrih, Jacques Liandrat. Comparison of different interpolation operators including nonlinear ă subdivision schemes in the simulation of particle trajectories. Journal of Computational Physics, Elsevier, 2013, 236, pp.346-366. 〈10.1016/j.jcp.2012.11.025〉. 〈hal-01464719〉
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Stefano Lepri, Roberto Livi. Particle model for nonlocal heat transport in fusion plasmas. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2013, 87 (2), 〈10.1103/PhysRevE.87.023102〉. 〈hal-01464720〉 Plus de détails...
We present a simple stochastic, one-dimensional model for heat transfer in weakly collisional media as fusion plasmas. Energies of plasma particles are treated as lattice random variables interacting with a rate inversely proportional to their energy schematizing a screened Coulomb interaction. We consider both the equilibrium (microcanonical) and nonequilibrium case in which the system is in contact with heat baths at different temperatures. The model exhibits a characteristic length of thermalization that can be associated with an interaction mean free path and one observes a transition from ballistic to diffusive regime depending on the average energy of the system. A mean-field expression for heat flux is deduced from system heat transport properties. Finally, it is shown that the nonequilibrium steady state is characterized by long-range correlations. DOI: 10.1103/PhysRevE.87.023102
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Stefano Lepri, Roberto Livi. Particle model for nonlocal heat transport in fusion plasmas. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2013, 87 (2), 〈10.1103/PhysRevE.87.023102〉. 〈hal-01464720〉
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Hugo Bufferand, B. Bensiali, J. Bucalossi, G. Ciraolo, P. Genesio, et al.. Near wall plasma simulation using penalization technique with the transport code Soledge2D-EIRENE. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.445-448. 〈10.1016/j.jnucmat.2013.01.090〉. 〈hal-01101345〉 Plus de détails...
In order to model plasma interaction with full complexity of the geometry of PFCs, an immersed method to impose boundary conditions has been implemented in the transport code SolEdge2D. This penalization technique has proven to properly recover Bohm boundary conditions, including supersonic solutions at the sheath entrance. The role of the ionization source has been taken into account by coupling SolEdge2D with the 3D kinetic neutral code Eirene. Density regimes are properly recovered and major differences between core located and divertor located ionization source regimes are emphasized. One also presents main chamber wall recycling regime simulations that can now be addressed with simulations of the entire edge plasma up to the wall.
Hugo Bufferand, B. Bensiali, J. Bucalossi, G. Ciraolo, P. Genesio, et al.. Near wall plasma simulation using penalization technique with the transport code Soledge2D-EIRENE. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.445-448. 〈10.1016/j.jnucmat.2013.01.090〉. 〈hal-01101345〉
B. Bensiali, K. Bodi, G. Ciraolo, Philippe Ghendrih, J Liandrat. Comparison of different interpolation operators including nonlinear
subdivision schemes in the simulation of particle trajectories
. Journal of Computational Physics, Elsevier, 2013, pp.346-366. 〈hal-01266305〉 Plus de détails...
In this work, we compare different interpolation operators in the context of particle track- ing with an emphasis on situations involving velocity field with steep gradients. Since, in this case, most classical methods give rise to the Gibbs phenomenon (generation of oscil- lations near discontinuities), we present new methods for particle tracking based on sub- division schemes and especially on the Piecewise Parabolic Harmonic (PPH) scheme which has shown its advantage in image processing in presence of strong contrasts. First an ana- lytic univariate case with a discontinuous velocity field is considered in order to highlight the effect of the Gibbs phenomenon on trajectory calculation. Theoretical results are pro- vided. Then, we show, regardless of the interpolation method, the need to use a conserva- tive approach when integrating a conservative problem with a velocity field deriving from a potential. Finally, the PPH scheme is applied in a more realistic case of a time-dependent potential encountered in the edge turbulence of magnetically confined plasmas, to com- pare the propagation of density structures (turbulence bursts) with the dynamics of test particles. This study highlights the difference between particle transport and density trans- port in turbulent fields.
B. Bensiali, K. Bodi, G. Ciraolo, Philippe Ghendrih, J Liandrat. Comparison of different interpolation operators including nonlinear
subdivision schemes in the simulation of particle trajectories
. Journal of Computational Physics, Elsevier, 2013, pp.346-366. 〈hal-01266305〉
A. Paredes, Hugo Bufferand, F. Schwander, G. Ciraolo, E. Serre, et al.. Penalization technique to model wall-component impact on heat and mass transport in the tokamak edge. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.625-628. 〈10.1016/j.jnucmat.2013.01.131〉. 〈hal-01101342〉 Plus de détails...
The original and computationally efficient volume penalization technique Ref. [1], proposed for an isothermal plasma to recover the Bohm boundary condition at the plasma–obstacle interface, is extended to model 3D obstacles. It is then generalized to handle electron and ion temperatures in a 1D model. Results in 3D simulations show that the geometry of secondary limiter has an influence on the density and particle flux profiles, breaking its toroidal symmetry and introducing profile gaps of magnitude of 20%. On the other hand, the generalization of the penalization scheme to the non-isothermal case demands to deal with new Neumann conditions on the heat fluxes. Those boundary conditions require the introduction of new mask functions to ensure that the Bohm boundary condition remains satisfied.
A. Paredes, Hugo Bufferand, F. Schwander, G. Ciraolo, E. Serre, et al.. Penalization technique to model wall-component impact on heat and mass transport in the tokamak edge. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.625-628. 〈10.1016/j.jnucmat.2013.01.131〉. 〈hal-01101342〉
Eric Serre, Hugo Bufferand, A. Paredes, Frédéric Schwander, Guido Ciraolo, et al.. Numerical modeling of the impact of geometry and wall components on transport in the tokamak edge. Contributions to Plasma Physics, Wiley-VCH Verlag, 2012, 52 (5-6), pp.401-405. 〈10.1002/ctpp.201210023〉. 〈hal-00848473〉 Plus de détails...
Eric Serre, Hugo Bufferand, A. Paredes, Frédéric Schwander, Guido Ciraolo, et al.. Numerical modeling of the impact of geometry and wall components on transport in the tokamak edge. Contributions to Plasma Physics, Wiley-VCH Verlag, 2012, 52 (5-6), pp.401-405. 〈10.1002/ctpp.201210023〉. 〈hal-00848473〉
Olivier Izacard, Natalia Tronko, Cristel Chandre, Guido Ciraolo, Michel Vittot, et al.. Transport barrier for the radial diffusion due to the ExB drift motion of guiding centers in cylindrical confinement geometry. Plasma Physics and Controlled Fusion, IOP Publishing, 2011, 53 (12), pp.125008. 〈10.1088/0741-3335/53/12/125008〉. 〈hal-00542733v5〉 Plus de détails...
We consider the radial transport of test particles due to the ExB drift motion in the guiding center approximation. Using an explicit expression to modify the electrostatic potential, we show that it is possible to construct a transport barrier which suppresses radial transport. We propose an algorithm for the implementation of this local modification computed from an electrostatic potential known on a spatio-temporal grid. The number of particles which escape the inner region defined by the barrier measures the efficiency of the control. We show that the control is robust by showing a significant reduction of radial transport, when applied with a reduced number of probes aligned on a circle.
Olivier Izacard, Natalia Tronko, Cristel Chandre, Guido Ciraolo, Michel Vittot, et al.. Transport barrier for the radial diffusion due to the ExB drift motion of guiding centers in cylindrical confinement geometry. Plasma Physics and Controlled Fusion, IOP Publishing, 2011, 53 (12), pp.125008. 〈10.1088/0741-3335/53/12/125008〉. 〈hal-00542733v5〉
B. Saoutic, N. Dumas, Rémi Dumont, A. Durocher, F. X. Duthoit, et al.. Contribution of Tore Supra in preparation of ITER. Nuclear Fusion, IOP Publishing, 2011, 51 (9, SI), 〈10.1088/0029-5515/51/9/094014〉. 〈hal-01460107〉 Plus de détails...
Tore Supra routinely addresses the physics and technology of very long-duration plasma discharges, thus bringing precious information on critical issues of long pulse operation of ITER. A new ITER relevant lower hybrid current drive (LHCD) launcher has allowed coupling to the plasma a power level of 2.7 MW for 78 s, corresponding to a power density close to the design value foreseen for an ITER LHCD system. In accordance with the expectations, long distance (10 cm) power coupling has been obtained. Successive stationary states of the plasma current pro le have been controlled in real-time featuring (i) control of sawteeth with varying plasma parameters, (ii) obtaining and sustaining a `hot core' plasma regime, (iii) recovery from a voluntarily triggered deleterious magnetohydrodynamic regime. The scrape-off layer (SOL) parameters and power deposition have been documented during L-mode ramp-up phase, a crucial point for ITER before the X-point formation. Disruption mitigation studies have been conducted with massive gas injection, evidencing the difference between He and Ar and the possible role of the q = 2 surface in limiting the gas penetration. ICRF assisted wall conditioning in the presence of magnetic eld has been investigated, culminating in the demonstration that this conditioning scheme allows one to recover normal operation after disruptions. The effect of the magnetic eld ripple on the intrinsic plasma rotation has been studied, showing the competition between turbulent transport processes and ripple toroidal friction. During dedicated dimensionless experiments, the effect of varying the collisionality on turbulence wavenumber spectra has been documented, giving new insight into the turbulence mechanism. Turbulence measurements have also allowed quantitatively comparing experimental results with predictions by 5D gyrokinetic codes: numerical results simultaneously match the magnitude of effective heat diffusivity, rms values of density uctuations and wavenumber spectra. A clear correlation between electron temperature gradient and impurity transport in the very core of the plasma has been observed, strongly suggesting the existence of a threshold above which transport is dominated by turbulent electron modes. Dynamics of edge turbulent uctuations has been studied by correlating data from fast imaging cameras and Langmuir probes, yielding a coherent picture of transport processes involved in the SOL.
B. Saoutic, N. Dumas, Rémi Dumont, A. Durocher, F. X. Duthoit, et al.. Contribution of Tore Supra in preparation of ITER. Nuclear Fusion, IOP Publishing, 2011, 51 (9, SI), 〈10.1088/0029-5515/51/9/094014〉. 〈hal-01460107〉
Olivier Izacard, Cristel Chandre, Emanuele Tassi, Guido Ciraolo. Gyromap for a two-dimensional Hamiltonian fluid model derived from Braginskii's closure for magnetized plasmas. Physics of Plasmas, American Institute of Physics, 2011, 18 (6), pp.062105. 〈10.1063/1.3591364〉. 〈hal-00575638v2〉 Plus de détails...
We consider a plasma described by means of a two-dimensional fluid model across a constant but non-uniform magnetic field B = B(x,y) z. The dynamical evolution of the density and the vorticity takes into account the interchange instability and magnetic field inhomogeneities. First, in order to described the Finite Larmor Radius effects we apply the gyromap to build a Hamiltonian model with ion temperature from a cold-ion model. Second, we show that the gyromap is justified using Braginskii's closure for the stress tensor as well as an apt ordering on the fluctuating quantities.
Olivier Izacard, Cristel Chandre, Emanuele Tassi, Guido Ciraolo. Gyromap for a two-dimensional Hamiltonian fluid model derived from Braginskii's closure for magnetized plasmas. Physics of Plasmas, American Institute of Physics, 2011, 18 (6), pp.062105. 〈10.1063/1.3591364〉. 〈hal-00575638v2〉
Hugo Bufferand, Guido Ciraolo, Livia Isoardi, Guillaume Chiavassa, Frédéric Schwander, et al.. Applications of SOLEDGE-2D code to complex SOL configurations and analysis of Mach probe measurements. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S589-S592. 〈10.1016/j.jnucmat.2010.11.037〉. 〈hal-00848483〉 Plus de détails...
A series of experiments dedicated to the determination of the ballooning nature of the edge and SOL transport has been achieved on Tore Supra and , proposing a quantitative characterization of the radial flux that enters the SOL. The aim of this paper is to back up the interpretation of these probe flow measurements making use of SOLEDGE-2D code. In particular, this fluid code allows one to study density and parallel momentum transport in a 2D geometry including edge and SOL region. Moreover, thanks to an appropriate numerical technique recently proposed and , SOLEDGE-2D code is also able to deal with a complex geometry of plasma facing components including main and secondary limiters.
Hugo Bufferand, Guido Ciraolo, Livia Isoardi, Guillaume Chiavassa, Frédéric Schwander, et al.. Applications of SOLEDGE-2D code to complex SOL configurations and analysis of Mach probe measurements. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S589-S592. 〈10.1016/j.jnucmat.2010.11.037〉. 〈hal-00848483〉
Philippe Ghendrih, K. Bodi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, et al.. Transition to supersonic flows in the edge plasma. Plasma Physics and Controlled Fusion, IOP Publishing, 2011, 53 (5), pp.054019. 〈10.1088/0741-3335/53/5/054019〉. 〈hal-00848545〉 Plus de détails...
With a proper choice of a single dimensionless control parameter one describes the transition between subsonic and supersonic flows as a bifurcation. The bifurcation point is characterized by specific properties of the control parameter: the control parameter has a vanishing derivative in space and takes the maximum possible value equal to 1. This method is then applied to the sheath plasma with constant temperatures, allowing one to recover the Bohm boundary condition as well as the location of the point where the bifurcation takes place. This analysis is extended to fronts, rarefaction waves and divertor plasmas. Two cases are found, those where departure from quasineutrality is mandatory to generate a maximum in the variation of the control parameter (sheath and fronts) and those where the physics of the quasineutral plasma can generate such a maximum (rarefaction waves and supersonic flow in divertors). The conditions that are required to recover the Bohm condition, when modelling the wall using the penalization technique, are also addressed and generalized.
Philippe Ghendrih, K. Bodi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, et al.. Transition to supersonic flows in the edge plasma. Plasma Physics and Controlled Fusion, IOP Publishing, 2011, 53 (5), pp.054019. 〈10.1088/0741-3335/53/5/054019〉. 〈hal-00848545〉
Nicolas Fedorczak, James Paul Gunn, Guido Ciraolo, Hugo Bufferand, Livia Isoardi, et al.. Experimental investigation on the poloidal extent of the turbulent radial flux in tokamak scrape-off layer. Journal of Nuclear Materials, Elsevier, 2011, 415 (1, Supplement 1), pp.S467-S470. 〈10.1016/j.jnucmat.2010.10.034〉. 〈hal-01024052〉 Plus de détails...
A consistent description of scrape-off layer transport is built from multi-diagnostic observations in ohmic discharges in Tore Supra. Fast imaging reveals the existence of relatively large filamentary structures on the low field side but not on the high field side of the torus. These filaments can exist either on open or closed magnetic flux surfaces and have a finite parallel extent from the outboard midplane. Probe electrostatic turbulence measured at the top of the plasma corresponds to the ExB convection of density burst, understood as the signature of filament propagation. Independent experiments on time-averaged parallel flows measured with a Mach probe lead to a poloidal mapping of the strongly asymmetric radial flux. This flux is centered at the outboard midplane and its poloidal half width is about 50°. The local turbulent flux on the top is consistent with the mapping.
Nicolas Fedorczak, James Paul Gunn, Guido Ciraolo, Hugo Bufferand, Livia Isoardi, et al.. Experimental investigation on the poloidal extent of the turbulent radial flux in tokamak scrape-off layer. Journal of Nuclear Materials, Elsevier, 2011, 415 (1, Supplement 1), pp.S467-S470. 〈10.1016/j.jnucmat.2010.10.034〉. 〈hal-01024052〉
A. Paredes, Eric Serre, Livia Isoardi, Guillaume Chiavassa, Guido Ciraolo, et al.. Boundary conditions at the limiter surface obtained in the modelling of plasma wall interaction with a penalization technique. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S579-S583. 〈10.1016/j.jnucmat.2010.12.247〉. 〈hal-00848532〉 Plus de détails...
Isoardi et al. [1] recently proposed a penalization technique to model solid plasma facing components that treats a solid obstacle as a sink region corresponding to the strong plasma recombination in the solid state material. A major advantage of this approach is that it produces a system that can be solved in an obstacle free domain, thus allowing the use of powerful numerical algorithms. Such a technique implemented in a minimal transport model for ionic density and parallel momentum appeared to exhibit a Mach-1 transition at the boundary layer between the plasma presheath and the limiter region. In this paper, we reconsider this result by analysing the physics of detached plasmas that are governed both by strong recombination and plasma pressure decrease, as imposed by the penalization technique within the limiter region. The analysis provides a unique control parameter A=Γcsmi/ΠA=Γcsmi/Π (Γ being the parallel particles flux, cs the sound speed, mi the ionic mass and Π the total plasma pressure) that allows one to understand the results of the penalization technique for the Mach-1 transition.
A. Paredes, Eric Serre, Livia Isoardi, Guillaume Chiavassa, Guido Ciraolo, et al.. Boundary conditions at the limiter surface obtained in the modelling of plasma wall interaction with a penalization technique. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S579-S583. 〈10.1016/j.jnucmat.2010.12.247〉. 〈hal-00848532〉
Guilhem Dif-Pradalier, J Gunn, Guido Ciraolo, C Chang, Guillaume Chiavassa, et al.. The Mistral base case to validate kinetic and fluid turbulence transport codes of the edge and SOL plasmas. Journal of Nuclear Materials, Elsevier, 2011, 415, 〈10.1016/j.jnucmat.2010.12.035〉. 〈cea-01468372〉 Plus de détails...
Experimental data from the Tore Supra experiments are extrapolated in the SOL and edge to investigate the Kelvin–Helmholtz instability. The linear analysis indicates that a large part of the SOL is rather unstable. The effort is part of the setup of the Mistral base case that is organised to validate the codes and address new issues on turbulent edges, including the comparison of kinetic and fluid modelling in the edge plasma.
Guilhem Dif-Pradalier, J Gunn, Guido Ciraolo, C Chang, Guillaume Chiavassa, et al.. The Mistral base case to validate kinetic and fluid turbulence transport codes of the edge and SOL plasmas. Journal of Nuclear Materials, Elsevier, 2011, 415, 〈10.1016/j.jnucmat.2010.12.035〉. 〈cea-01468372〉
Livia Isoardi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, Frédéric Schwander, et al.. 2D modelling of electron and ion temperature in the plasma edge and SOL. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S574-S578. 〈10.1016/j.jnucmat.2010.12.318〉. 〈hal-00848528〉 Plus de détails...
We are interested here in modelling the electron and ion temperature fields, Te and Ti respectively, in order to understand the main trends that govern the ratio Ti/Te that is being better documented in the SOL with RFA probes and . The experimental evidence gathered from several devices indicates that this temperature ratio significantly exceeds unity in most data sets that have been analysed, including measurements in the SOL of limiter devices like Tore Supra. Several issues of interest have been addressed with this version of the SOLEDGE-2D code. First, we have analysed the width of the SOL heat channels to the wall components and compared these values to analytical expressions. The key control mechanism of the width of the SOL heat channel is given by a balance between the sheath boundary conditions and the transverse transport. More advanced simulations address the interplay between the edge and SOL plasma allowing one to recover regimes with Ti/Te > 1.
Livia Isoardi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, Frédéric Schwander, et al.. 2D modelling of electron and ion temperature in the plasma edge and SOL. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S574-S578. 〈10.1016/j.jnucmat.2010.12.318〉. 〈hal-00848528〉
Guillaume Chiavassa, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Hervé Guillard, et al.. Parallel expansion of density bursts. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S613-S616. 〈10.1016/j.jnucmat.2010.10.086〉. 〈hal-00848522〉 Plus de détails...
Evidence of poloidally localized cross-field transport in experiments and theoretical analysis of turbulence transport governs the onset of parallel transport towards equilibrium. When cross-field transport appears in bursts, both for ELM relaxation events and microturbulence, the parallel transport of particles is shown to generate fronts that propagate with supersonic velocities. It is shown that after a short transient the density structure is no longer monotonic and that the two fronts (one co, the other counter the magnetic field) are independent. Furthermore, the time trace of the particle flux at a given location is characterized by a sharp rise followed by a longer time scale relaxation. Comparing the time delay and magnitude of the density burst at two locations allows to estimate the magnitude and the location of the generation of the front.
Guillaume Chiavassa, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Hervé Guillard, et al.. Parallel expansion of density bursts. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S613-S616. 〈10.1016/j.jnucmat.2010.10.086〉. 〈hal-00848522〉
Frédéric Schwander, Guillaume Chiavassa, Guido Ciraolo, Philippe Ghendrih, Livia Isoardi, et al.. Parallel shear flow instability in the tokamak edge. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S601-S604. 〈10.1016/j.jnucmat.2010.10.073〉. 〈hal-00848536〉 Plus de détails...
The transition between the core and scrape-off layer of a tokamak corresponds to a marked momentum shear layer, owing to sheath acceleration on limiters which drives near-sonic flows along the plasma magnetic field in the scrape-off layer, and a parallel shear flow instability can possibly be triggered. The possibility of this instability driven by the velocity gradient is investigated numerically, using a minimum model of particle and parallel momentum transport in the edge of a tokamak, in a computational domain modelling a limiter plasma with background turbulence modelled as an effective diffusion. It is found that unstable regions can exist in the vicinity of a limiter, in agreement with experimental findings, when momentum radial transport - and therefore coupling between SOL and core flows - is sufficiently weak. Instability is reinforced by core rotation, and is found to be maximum downstream of the limiter (with respect to the core plasma flow).
Frédéric Schwander, Guillaume Chiavassa, Guido Ciraolo, Philippe Ghendrih, Livia Isoardi, et al.. Parallel shear flow instability in the tokamak edge. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S601-S604. 〈10.1016/j.jnucmat.2010.10.073〉. 〈hal-00848536〉
Livia Isoardi, Guillaume Chiavassa, Guido Ciraolo, Pierre Haldenwang, Eric Serre, et al.. Penalization modeling of a limiter in the Tokamak edge plasma. Journal of Computational Physics, Elsevier, 2010, 229 (6), pp.2220-2235. 〈10.1016/j.jcp.2009.11.031〉. 〈hal-00386101v2〉 Plus de détails...
An original penalization method is applied to model the interaction of magnetically confined plasma with limiter in the frame of minimal transport model for ionic density and parallel momentum. The limiter is considered as a pure particle sink for the plasma and consequently the density and the momentum are enforced to be zero inside. Comparisons of the numerical results with one dimensional analytical solutions show a very good agreement. In particular, presented method provides a plasma velocity which is almost sonic at the boundaries obstacles as expected from the sheath conditions through the Bohm criterion. The new system being solved in an obstacle free domain, an efficient pseudo-spectral algorithm based on a Fast Fourier transform is also proposed, and associated with an exponential filtering of the unphysical oscillations due to Gibbs phenomenon. Finally, the efficiency of the method is illustrated by investigating the flow spreading from the plasma core to the Scrape Off Layer at the wall in a two-dimensional system with one then two limiters neighboring.
Livia Isoardi, Guillaume Chiavassa, Guido Ciraolo, Pierre Haldenwang, Eric Serre, et al.. Penalization modeling of a limiter in the Tokamak edge plasma. Journal of Computational Physics, Elsevier, 2010, 229 (6), pp.2220-2235. 〈10.1016/j.jcp.2009.11.031〉. 〈hal-00386101v2〉
Cristel Chandre, Guido Ciraolo, Michel Vittot. Reduction of the chaotic transport of impurities in turbulent magnetized plasmas. M.A.F. Sanjuan and C. Grebogi. Recent Progress in Controlling Chaos, World Scientific, pp.1, 2010, Stability, Vibration and Control of Systems - Series B. 〈hal-00424256〉 Plus de détails...
The chaotic transport of charged particles in a turbulent electrostatic potential sets the conditions of a severe limitation to the plasma confinement in devices such as tokamaks. In this chapter, we consider the motion of impurities driven by the ExB velocity where a strong magnetic field B (which allows for the guiding center approximation) is uniform and constant, and a turbulent electric field is obtained from models or from numerical fluid codes. Hamiltonian dynamics rule the transport properties of these impurities. Therefore a technique to reduce chaotic diffusion in Hamiltonian systems is able to address the issue of reducing the radial transport of impurities under some approximations. The general idea is to build barriers in phase space by a small and apt modification of the Hamiltonian. We show numerically that such perturbations are able to drastically reduce the diffusion of test-particles, and we discuss the robustness of such additional modifications.
Cristel Chandre, Guido Ciraolo, Michel Vittot. Reduction of the chaotic transport of impurities in turbulent magnetized plasmas. M.A.F. Sanjuan and C. Grebogi. Recent Progress in Controlling Chaos, World Scientific, pp.1, 2010, Stability, Vibration and Control of Systems - Series B. 〈hal-00424256〉
Livia Isoardi, Guido Ciraolo, Guillaume Chiavassa, Pierre Haldenwang, Eric Serre, et al.. Modelling SOL flow pattern spreading in the edge plasma. Journal of Nuclear Materials, Elsevier, 2009, 390-391, pp.388-391. 〈10.1016/j.jnucmat.2009.01.088〉. 〈hal-00848559〉 Plus de détails...
The transition region between closed and open magnetic flux surfaces plays a crucial role for tokamak performances. Appropriate understanding of the edge region remains a major challenge owing to several open issues as momentum transport, turbulence overshoot or neutral penetration. We consider here a transport model system to investigate the propagation of parallel momentum from the SOL into the core plasma and vice-versa. The numerical results show that for small values of the radial diffusion coefficient, the density profile decays exponentially from the core to the SOL as predicted by 1D analytical solution. A spreading of the parallel momentum from the SOL to the core is observed, with the presence of non-zero velocities also in the regions far from the SOL. The effect of an imposed rotation of the core plasma is investigated as well as the dynamics of an overdensity imposed in the core plasma.
Livia Isoardi, Guido Ciraolo, Guillaume Chiavassa, Pierre Haldenwang, Eric Serre, et al.. Modelling SOL flow pattern spreading in the edge plasma. Journal of Nuclear Materials, Elsevier, 2009, 390-391, pp.388-391. 〈10.1016/j.jnucmat.2009.01.088〉. 〈hal-00848559〉
Natalia Tronko, Michel Vittot, Cristel Chandre, Philippe Ghendrih, Guido Ciraolo. Barriers for the reduction of transport due to the EXB drift in magnetized plasmas. Journal of Physics A: Mathematical and Theoretical, IOP Publishing, 2009, 42 (42(2009)), pp.085501. 〈hal-00354173〉 Plus de détails...
We consider a 1 1/2degrees of freedom Hamiltonian dynamical system, which models the chaotic dynamics of charged test-particles in a turbulent electric field, across the confining magnetic field in controlled thermonuclear fusion devices. The external electric field E = −∇V is modeled by a phenomenological potential V and the magnetic field B is considered uniform. It is shown that, by introducing a small additive control term to the external electric field, it is possible to create a transport barrier for this dynamical system. The robustness of this control method is also investigated. This theoretical study indicates that alternative transport barriers can be triggered without requiring a control action on the device scale as in present Internal Transport Barriers (ITB).
Natalia Tronko, Michel Vittot, Cristel Chandre, Philippe Ghendrih, Guido Ciraolo. Barriers for the reduction of transport due to the EXB drift in magnetized plasmas. Journal of Physics A: Mathematical and Theoretical, IOP Publishing, 2009, 42 (42(2009)), pp.085501. 〈hal-00354173〉
Journal: Journal of Physics A: Mathematical and Theoretical
Guido Ciraolo, Philippe Ghendrih, Yanick Sarazin, Cristel Chandre, Ricardo Lima, et al.. Control of test particle transport in a turbulent electrostatic model of the Scrape Off Layer. Journal of Nuclear Materials, Elsevier, 2007, 363-365, pp.550-554. 〈hal-00183859〉 Plus de détails...
The ${\bm E}\times{\bm B}$ drift motion of charged test particle dynamics in the Scrape Off Layer (SOL)is analyzed to investigate a transport control strategy based on Hamiltonian dynamics. We model SOL turbulence using a 2D non-linear fluid code based on interchange instability which was found to exhibit intermittent dynamics of the particle flux. The effect of a small and appropriate modification of the turbulent electric potential is studied with respect to the chaotic diffusion of test particle dynamics. Over a significant range in the magnitude of the turbulent electrostatic field, a three-fold reduction of the test particle diffusion coefficient is achieved.
Guido Ciraolo, Philippe Ghendrih, Yanick Sarazin, Cristel Chandre, Ricardo Lima, et al.. Control of test particle transport in a turbulent electrostatic model of the Scrape Off Layer. Journal of Nuclear Materials, Elsevier, 2007, 363-365, pp.550-554. 〈hal-00183859〉