Impact des ions rapides sur la microturbulence dans les plasmas de fusion

The exploitation of magnetically confined fusion plasmas as a sustainable and clean energy source is limited by the radially outward turbulent transport. Such transport is mainly induced by microinstabilities. Next-generation fusion devices will be mainly heated by the alpha particles born from the nuclear fusion reactions. Alpha particles must be well confined in order to transfer their energy to the bulk ions. However, very little knowledge is available regarding the interaction between alpha particles and microturbulence. Thus, unexpected turbulence and transport regimes may lead to further detrimental effects on the performance of future alpha-heated devices. The study of a tokamak scenario which can mimic the experimental conditions expected in future devices is hence crucial. Numerical investigations on the impact of fast ions on the turbulent transport driven by Ion Temperature Gradient and Trapped Electron Mode instabilities in real experiments have been carried out. It is shown that a suppression of the ion-scale turbulent transport may be achieved. Alfvén Eigenmodes (AEs) destabilized by the highly energetic ions through a wave-particle interaction play an essential role in the multi-scale mechanism leading to the turbulence suppression. Deep analyses further highlight the possibility to recognize hallmarks of the ion-scale transport reduction, regardless the dominant turbulent regime.L'exploitation des plasmas de fusion magnétiquement confinés en tant que source d'énergie durable et propre est limitée par le transport turbulent radial vers l'extérieur. Ce transport est principalement induit par les micro-instabilités. Les dispositifs de fusion de la prochaine génération seront principalement chauffés par les particules alpha produites par les réactions de fusion nucléaire. Les particules alpha doivent être bien confinées afin de transférer leur énergie aux ions thermique. Cependant, on dispose de très peu de connaissances sur l'interaction entre les particules alpha et les micro-turbulences. Ainsi, des régimes de turbulence et de transport inattendus peuvent avoir des effets néfastes sur les performances des futurs réacteurs chauffés par les particules alpha. L'étude d'un scénario de tokamak qui peut imiter les conditions expérimentales attendues dans les futurs réacteurs est donc cruciale. Des études numériques sur l'impact des ions rapides sur le transport turbulent induit par le gradient de température des ions et les instabilités du mode des électrons piégés dans des expériences réelles ont été réalisées. Il est démontré qu'une suppression du transport turbulent à l'échelle des ions peut être obtenue. Les modes d'Alfvén déstabilisés par les ions hautement énergétiques, à travers une interaction onde-particule, jouent un rôle essentiel dans le mécanisme multi-échelle qui conduit à la suppression de la turbulence. Des analyses approfondies soulignent en outre la possibilité de reconnaître les caractéristiques de la réduction du transport à l'échelle des ions, quel que soit le régime turbulent dominant

Impact des ions rapides sur la microturbulence dans les plasmas de fusion

L'exploitation des plasmas de fusion magnétiquement confinés en tant que source d'énergie durable et propre est limitée par le transport turbulent radial vers l'extérieur. Ce transport est principalement induit par les micro-instabilités. Les future réacteurs seront principalement chauffés par les particules alpha produites par les réactions de fusion nucléaire. Les particules alpha doivent être bien confinées afin de transférer leur énergie aux ions thermiques. Cependant, on a aujourd'hui très peu de connaissances sur l'interaction entre les particules alpha et la microturbulence. Ainsi, des régimes de turbulence et de transport inattendus peuvent avoir des effets néfastes sur les performances des futurs réacteurs chauffés par les particules alpha. L'étude d'un scénario de tokamak qui peut imiter les conditions expérimentales attendues dans les futurs réacteurs est donc cruciale. Des études numériques sur l'impact des ions rapides hautement énergétiques, imitant la dynamique des particules alpha, sur le transport turbulent provoqué par le gradient de température des ions et les instabilités du mode des électrons piégés ont été réalisées. Il est démontré qu'une suppression du transport turbulent à l'échelle ionique peut être obtenue en présence de tels ions hautement énergétiques. Les modes d'Alfvén (AEs), déstabilisés par les ions hautement énergétiques à travers une interaction onde-particule, jouent un rôle essentiel dans le mécanisme multi-échelle menant à la suppression de la turbulence. Des analyses approfondies soulignent en outre la possibilité de reconnaître les caractéristiques de la réduction du transport à l'échelle des ionsThe exploitation of magnetically confined fusion plasmas as a sustainable and clean energy source is limited by the radially outward turbulent transport. Such transport is mainly induced by microinstabilities. Next-generation fusion devices will be mainly heated by the alpha particles born from the nuclear fusion reactions. Alpha particles must be well confined in order to transfer their energy to the bulk ions. However, very little knowledge is available regarding the interaction between alpha particles and microturbulence. Thus, unexpected turbulence and transport regimes may lead to further detrimental effects on the performance of future alpha-heated devices. The study of a tokamak scenario which can mimic the experimental conditions expected in future devices is hence crucial. Numerical investigations on the impact of highly energetic fast ions, mimicking the alpha particle dynamics, on the turbulent transport driven by Ion Temperature Gradient and Trapped Electron Mode instabilities have been carried out in a validated framework. It is shown that a suppression of the ion-scale turbulent transport may be achieved in the presence of such highly energetic ions. Alfvén Eigenmodes (AEs), destabilized by the highly energetic ions through a wave-particle interaction, play an essential role in the multi-scale mechanism leading to the turbulence suppression. Deep analyses further highlight the possibility to recognize hallmarks of the ion-scale transport reduction, regardless the dominant turbulent regim

Impact des ions rapides sur la microturbulence dans les plasmas de fusion

The exploitation of magnetically confined fusion plasmas as a sustainable and clean energy source is limited by the radially outward turbulent transport. Such transport is mainly induced by microinstabilities. Next-generation fusion devices will be mainly heated by the alpha particles born from the nuclear fusion reactions. Alpha particles must be well confined in order to transfer their energy to the bulk ions. However, very little knowledge is available regarding the interaction between alpha particles and microturbulence. Thus, unexpected turbulence and transport regimes may lead to further detrimental effects on the performance of future alpha-heated devices. The study of a tokamak scenario which can mimic the experimental conditions expected in future devices is hence crucial. Numerical investigations on the impact of fast ions on the turbulent transport driven by Ion Temperature Gradient and Trapped Electron Mode instabilities in real experiments have been carried out. It is shown that a suppression of the ion-scale turbulent transport may be achieved. Alfvén Eigenmodes (AEs) destabilized by the highly energetic ions through a wave-particle interaction play an essential role in the multi-scale mechanism leading to the turbulence suppression. Deep analyses further highlight the possibility to recognize hallmarks of the ion-scale transport reduction, regardless the dominant turbulent regime.L'exploitation des plasmas de fusion magnétiquement confinés en tant que source d'énergie durable et propre est limitée par le transport turbulent radial vers l'extérieur. Ce transport est principalement induit par les micro-instabilités. Les dispositifs de fusion de la prochaine génération seront principalement chauffés par les particules alpha produites par les réactions de fusion nucléaire. Les particules alpha doivent être bien confinées afin de transférer leur énergie aux ions thermique. Cependant, on dispose de très peu de connaissances sur l'interaction entre les particules alpha et les micro-turbulences. Ainsi, des régimes de turbulence et de transport inattendus peuvent avoir des effets néfastes sur les performances des futurs réacteurs chauffés par les particules alpha. L'étude d'un scénario de tokamak qui peut imiter les conditions expérimentales attendues dans les futurs réacteurs est donc cruciale. Des études numériques sur l'impact des ions rapides sur le transport turbulent induit par le gradient de température des ions et les instabilités du mode des électrons piégés dans des expériences réelles ont été réalisées. Il est démontré qu'une suppression du transport turbulent à l'échelle des ions peut être obtenue. Les modes d'Alfvén déstabilisés par les ions hautement énergétiques, à travers une interaction onde-particule, jouent un rôle essentiel dans le mécanisme multi-échelle qui conduit à la suppression de la turbulence. Des analyses approfondies soulignent en outre la possibilité de reconnaître les caractéristiques de la réduction du transport à l'échelle des ions, quel que soit le régime turbulent dominant

Parametric Validation of the Reservoir-Computing-Based Machine Learning Algorithm Applied to Lorenz System Reconstructed Dynamics

International audienceA detailed parametric analysis is presented, where the recent method based on the Reservoir Computing paradigm, including its statistical robustness, is studied. It is observed that the prediction capabilities of the Reservoir Computing approach strongly depend on the random initialisation of both the input and the reservoir layers. Special emphasis is put on finding the region in the hyperparameter space where the ensemble-averaged training and generalization errors together with their variance are minimized. The statistical analysis presented here is based on the Projection on Proper Elements (PoPe) method [T. Cartier-Michaud et al., Phys. Plasmas 23, 020702 (2016)]

Parametric Validation of the Reservoir Computing–Based Machine Learning Algorithm Applied to Lorenz System Reconstructed Dynamics

International audienceA detailed parametric analysis is presented, where the recent method based on the reservoir computing paradigm, including its statistical robustness, is studied. It is observed that the prediction capabilities of the reservoir computing approach strongly depend on the random initialization of both the input and the reservoir layers. Special emphasis is put on finding the region in the hyperparameter space where the ensemble-averaged training and generalization errors together with their variance are minimized. The statistical analysis presented here is based on the projection on proper elements method

Improvement of the clinical-care pathway of inguinal hernia surgery: a mathematical model for implementing a feasibility study

The best public sector performance has long been a topic at the core of political, social and economic debate. Public management policies and the growing adoption of corporate governance principles support the transition towards models capable of guaranteeing greater control of results in terms of efficiency, effectiveness, and outcome. Healthcare systems are an example of public service. Due to their high management costs, healthcare systems are often under pressure, especially when there is a need to widen access, to improve their efficiency and their care quality and to reduce inequalities. Operations Management (OM) approaches actively support this path. This article describes a retrospective analysis, in which a surgical rescheduling plan of a hospital in northern Italy (consisting of 6 structures distributed throughout wide provincial area serving over 530,000 inhabitants) has been produced, with particular reference to inguinal hernia surgery as health service subject to optimization. The current situation ("as is" scenario) is characterized by a strong concentration of complex and urgent surgical interventions in two hospital facilities of the hospital network, which are further burdened by less complex planned interventions. A linear integer model has been developed, to determine a possible optimized scenario for the redistribution of surgical interventions, trying to leave complex and urgent cases in the two reference structures, but relieving them of the other cases through a better distribution in the other structures of the network. The costs were the driver used for the scheduling, which resulted to be considerably reduced in the new proposed configuration

Effects of the parallel flow shear on the ITG-driven turbulent transport in tokamak plasmas

International audienceAbstract The impact of the parallel flow shear on the tokamak plasma stability and turbulent transport driven by the ion temperature gradient (ITG) modes is analyzed by means of local gyrokinetic numerical analyses. It is shown that the parallel flow shear increases the ITG growth rate in the linear regime, and induces a broadening and shift of the radial spectrum. Then, the different effects of the finite parallel shear on the ITG turbulence characteristics are deeply analyzed in the nonlinear regime. These studies highlight that a reduction of the thermal-ion turbulent heat flux is induced by a complex mechanism involving the nonlinear generation of an enhanced zonal flow activity. Indeed, the turbulent sources of the zonal flows are increased by the introduction of the finite parallel flow shear in the system, beneficially acting on the saturation level of the ITG turbulence. The study has been carried out for the Waltz standard case below the critical threshold of the destabilization of the parallel velocity gradient instability, and then generalized to a selected pulse of a recent JET scenario with substantial toroidal rotation in the edge plasma region. It is, thus, suggested that the investigated complex mechanism triggered by the finite parallel flow shear reducing the ITG turbulent heat fluxes could be complementary to the well-established perpendicular flow shear in a region with sufficiently large plasma toroidal rotation

Exploring New Frontiers of the Ion-Scale Turbulence Suppression by Fast Ions

Understanding and controlling the turbulent transport developing at the ion-scale, which strongly limits the thermal confinement in tokamaks, is crucial in view of the steady-state ITER operations. As ITER will be mainly heated by the fusion-born alpha particles, the development of ITER-relevant scenarios, together with complex numerical analyses, is crucial in order to study the possible effects of the alpha particles on turbulence regimes to date not explored in detail. Therefore, the present work aims at unveiling further steps towards the complete understanding of the impact of fast ions on the microturbulence, by extending the frontiers of our knowledge towards MeV-range of fast ion energy and turbulence patterns different to the well-established ITG, by means of very demanding gyrokinetic numerical analyses.5th Asia Pacific Conference on Plasma Physic