Periodic Reporting for period 4 - 3D-FIREFLUC (Taming the particle transport in magnetized plasmas via perturbative fields)
Periodo di rendicontazione: 2023-11-01 al 2024-04-30
Wave-particle interactions are ubiquitous in nature and play a fundamental role in astrophysical and fusion plasmas. In solar plasmas, magnetohydrodynamic (MHD) fluctuations are thought to be responsible for the heating of the solar corona and the generation of the solar wind. In magnetically confined fusion (MCF) devices, enhanced particle transport induced by MHD fluctuations can deteriorate the plasma confinement, and also endanger the device integrity. MCF devices are an ideal testbed to verify current models and develop mitigation / protection techniques.
In this project we aim to provide a solid understanding of the interaction between particles and MHD instabilities in the presence of electric fields and plasma currents with the ultimate goal to provide control techniques to tame the MHD induced particle transport in a fusion plasma. To this end, we have developed innovative diagnostic techniques which will soon be exploited scientifically as we achieve the first measurements. Combined with state-of-the-art hybrid MHD codes, a deep insight into the underlying physics mechanism of wave-particle interactions will be gained.
We have successfully developed, commissioned and operated two innovative scintillation imaging diagnostics at the ASDEX Upgrade tokamak. The diagnostics provide, for the first time, unprecedented spatio-temporal measurements of the confined energetic ion population and edge current density and filamentary transport of electron density fluctuations. We were able to decipher important wave-particle interactions between several magnetohydrodynamic fluctuations and the ion species (both thermal and supra-thermal) by combining both experiment and theory. Non-linear hybrid kinetic-MHD simulations of our experiments reveal that the kinetic treatment of energetic ions is key in understanding their effects on the spatio-temporal structure of ELMs in tokamaks. The resonant interaction between the drift orbits of the edge fast-ion population and the ELM electromagnetic perturbations results in a net exchange of energy and momentum between the wave and particles, which ultimately determines the spatio-temporal structure of the ELMs. We revelead that the ion and electron energy transport recover on different timescales, with the electrons recovering on a slower timescale. Combining the measurements with modelling, we were able to identify that the dominant mechanism for the additional energy transport in the electron channel, that could cause the delay in the electron temperature gradient recovery, is due to the depletion of energy caused by the ELM itself.
In this project we aim to provide a solid understanding of the interaction between particles and MHD instabilities in the presence of electric fields and plasma currents with the ultimate goal to provide control techniques to tame the MHD induced particle transport in a fusion plasma. To this end, we have developed innovative diagnostic techniques which will soon be exploited scientifically as we achieve the first measurements. Combined with state-of-the-art hybrid MHD codes, a deep insight into the underlying physics mechanism of wave-particle interactions will be gained.
We have successfully developed, commissioned and operated two innovative scintillation imaging diagnostics at the ASDEX Upgrade tokamak. The diagnostics provide, for the first time, unprecedented spatio-temporal measurements of the confined energetic ion population and edge current density and filamentary transport of electron density fluctuations. We were able to decipher important wave-particle interactions between several magnetohydrodynamic fluctuations and the ion species (both thermal and supra-thermal) by combining both experiment and theory. Non-linear hybrid kinetic-MHD simulations of our experiments reveal that the kinetic treatment of energetic ions is key in understanding their effects on the spatio-temporal structure of ELMs in tokamaks. The resonant interaction between the drift orbits of the edge fast-ion population and the ELM electromagnetic perturbations results in a net exchange of energy and momentum between the wave and particles, which ultimately determines the spatio-temporal structure of the ELMs. We revelead that the ion and electron energy transport recover on different timescales, with the electrons recovering on a slower timescale. Combining the measurements with modelling, we were able to identify that the dominant mechanism for the additional energy transport in the electron channel, that could cause the delay in the electron temperature gradient recovery, is due to the depletion of energy caused by the ELM itself.
We have successfully installed and commissioned the imaging diagnostics at the ASDEX Upgrade (AUG) tokamak in collaboration with the AUG team at the Max Planck Institute for Plasma Physics (IPP) in Garching, Germany. We have measured the confined energetic ions, edge currenty densisty and filamentary transport of electron density fluctuations in several plasma scenarios and carried out the data analysis and modelling. The results were published in several peer-review papers in Nuclear Fusion, Nuclear Materials and Energy, Plasma Physics and Controlled Fusion and Review of Scientific Instruments (see also list of publications). We have developed new deposition techniques of the scintillator screens and characterized the screens at the Centro Nacional de Aceleradores and the Materials Engineering Department in Seville and at IPP Garching. For the first time we have used these "in-house" scintillator screens in the plasma environment and they demonstrated their capability to deliver good signals and to endure the hostile environment. The first results on this milestone were published in Review of Scientific Instruments and Fusion Engineering and Design. The results were so successful that we were contacted by other groups to provide scintillation screens for their diagnostics. We also launched a new research line on improving the efficiency of the scintillating material.
Besides the installation and commissioning of the new diagnostics, we have also carried out first experiments on the wave-particle interaction of MHD instabilities on the ASDEX Upgrade tokamak. In particular, Edge Localized Modes (ELMs), Edge Harmonic Oscillations (EHO), plasma response due to externally applied 3D magnetic perturbations (MPs) as well as Alfvén eigenmodes driven unstable by NBI and ICRH ions were studied. The modelling on the interaction of ELMs with energetic ions was presented by one of my PhD students in an invited talk at the IAEA Technical Meeting 2022. His manuscript is currently under revision in Nature Physics. The transport analysis for the ELM cycles were presented in an invited talk at the European Physical Society Conference on Plasma Physics in Milan in 2019 and were published in Plasma Physics Controlled Fusion in 2020. In addition, we presented part of the results in a plenary talk on ELM-free confinement regimes at the 25th EU-US Transport Taskforce Meeting in 2021.
We have extended the 3D nonlinear hybrid kinetic MHD code MEGA with a realistic tokamak geometry model and a 3D wall for AUG. This was complemented by the implementation of synthetic diagnostics to diagnose the wave-particle interaction in modelling. This enables for the first time a detailed comparison to the experiment. In addition, we have carried out simple equilibrium calculations for a test case (published in Plasma Research Express and Fusion Engineering Design) and the plasma response has been implemented in MEGA for the ASDEX Upgrade tokamak. The wave-particle interactions arising due to externally applied magnetic perturbations have been simulated for ITER and published in Nuclear Fusion in 2021.
During 2021 we have also started a collaboration with the ERC group led by Prof. Katharina Schratz (ERC Starting Grant 2019 LAHACODE) on the implementation of advanced numerical schemes in MEGA and we have implemented an upgraded Runge-Kutta method in MEGA.
We developed a linear gyrokinetic theory for the wave and stability properties of low-frequency electromagnetic fluctuations in finite-beta anisotropic uniform plasmas. Unlike most of previous studies, the present theoretical framework includes full finite Larmor radius effect and wave-particle resonance, while the resultant model is still analytical tractable and offers a useful tool for gaining insights into the underlying physics. This result was published in Physical Review Letters and Physics of Plasmas.
Besides the installation and commissioning of the new diagnostics, we have also carried out first experiments on the wave-particle interaction of MHD instabilities on the ASDEX Upgrade tokamak. In particular, Edge Localized Modes (ELMs), Edge Harmonic Oscillations (EHO), plasma response due to externally applied 3D magnetic perturbations (MPs) as well as Alfvén eigenmodes driven unstable by NBI and ICRH ions were studied. The modelling on the interaction of ELMs with energetic ions was presented by one of my PhD students in an invited talk at the IAEA Technical Meeting 2022. His manuscript is currently under revision in Nature Physics. The transport analysis for the ELM cycles were presented in an invited talk at the European Physical Society Conference on Plasma Physics in Milan in 2019 and were published in Plasma Physics Controlled Fusion in 2020. In addition, we presented part of the results in a plenary talk on ELM-free confinement regimes at the 25th EU-US Transport Taskforce Meeting in 2021.
We have extended the 3D nonlinear hybrid kinetic MHD code MEGA with a realistic tokamak geometry model and a 3D wall for AUG. This was complemented by the implementation of synthetic diagnostics to diagnose the wave-particle interaction in modelling. This enables for the first time a detailed comparison to the experiment. In addition, we have carried out simple equilibrium calculations for a test case (published in Plasma Research Express and Fusion Engineering Design) and the plasma response has been implemented in MEGA for the ASDEX Upgrade tokamak. The wave-particle interactions arising due to externally applied magnetic perturbations have been simulated for ITER and published in Nuclear Fusion in 2021.
During 2021 we have also started a collaboration with the ERC group led by Prof. Katharina Schratz (ERC Starting Grant 2019 LAHACODE) on the implementation of advanced numerical schemes in MEGA and we have implemented an upgraded Runge-Kutta method in MEGA.
We developed a linear gyrokinetic theory for the wave and stability properties of low-frequency electromagnetic fluctuations in finite-beta anisotropic uniform plasmas. Unlike most of previous studies, the present theoretical framework includes full finite Larmor radius effect and wave-particle resonance, while the resultant model is still analytical tractable and offers a useful tool for gaining insights into the underlying physics. This result was published in Physical Review Letters and Physics of Plasmas.
The new imaging diagnostics developed and implemented in this project, combined with state-of-the-art hybrid-kinetic magnetohydrodynamic simulations, enable tracking the footprint of the interactions between magnetohydrodynamic waves and particles in a plasma and to investigate plasma physics phenomena that were previously inacessible. We have advanced our understanding of wave-particle interactions in magnetized plasmas and developed active control techniques to mitigate the particle transport and acceleration induced by magnetohydrodynamic fluctuations.