Periodic Reporting for period 4 - PI2FA (Partial Ionisation: Two-Fluid Approach)
Okres sprawozdawczy: 2023-03-01 do 2024-02-29
The PI2FA project aims to advance our understanding of the magnetized solar chromosphere using a novel multi-fluid plasma theory framework. Understanding the processes that produce non-thermal heat in the solar upper atmosphere and trigger energy eruptions is crucial for human civilization. Although direct spatially resolved measurements of magnetic energy release processes are challenging due to small scales, advances in 4-m class solar telescopes like DKIST and EST offer hope. However, sophisticated theories are essential for interpreting solar data accurately.
The solar atmosphere, spanning from the photosphere to the corona, exhibits significant structural and dynamic changes. The decrease in collisional coupling with height contributes to the complexity of the solar chromosphere, which acts as a boundary layer between the Sun's interior and the corona. Partially ionized conditions in the chromosphere have been underappreciated in solar physics, but recent advancements in computing enable the simulation of partial ionization effects and their consequences. Non-ideal plasma behavior due to neutrals may hold the key to solving chromospheric heating and dynamics puzzles, requiring a multi-fluid treatment for accurate description.
The PI2FA project focuses on creating and applying tools for multi-dimensional modeling of partially ionized chromospheric plasma based on the two-fluid multi-species formalism. Scientific questions include determining chromospheric heating mechanisms, creating multi-dimensional realistic models of the solar chromosphere incorporating ion-neutral effects, and understanding neutrals' role in prominence dynamics. By addressing fundamental mechanisms of energy propagation and exchange in complex plasmas, such as waves, instabilities, and plasma-radiation interactions, the project seeks to consolidate theoretical and numerical computational research in the field. Transitioning from one-dimensional idealized models to multi-dimensional simulations represents a crucial advancement, aligning with the evolving capabilities of solar observation technology.
By the project's conclusion, we significantly advanced our understanding of the processes energizing the partially ionized solar atmosphere. On one hand, we created extensions of multi-fluid theory for arbitrary collisional regimes and developed various computational-numerical tools for realistic modeling of partially ionized plasmas. On the other hand, through the application of these tools, we attained several significant scientific outcomes, detailed below.
The solar atmosphere, spanning from the photosphere to the corona, exhibits significant structural and dynamic changes. The decrease in collisional coupling with height contributes to the complexity of the solar chromosphere, which acts as a boundary layer between the Sun's interior and the corona. Partially ionized conditions in the chromosphere have been underappreciated in solar physics, but recent advancements in computing enable the simulation of partial ionization effects and their consequences. Non-ideal plasma behavior due to neutrals may hold the key to solving chromospheric heating and dynamics puzzles, requiring a multi-fluid treatment for accurate description.
The PI2FA project focuses on creating and applying tools for multi-dimensional modeling of partially ionized chromospheric plasma based on the two-fluid multi-species formalism. Scientific questions include determining chromospheric heating mechanisms, creating multi-dimensional realistic models of the solar chromosphere incorporating ion-neutral effects, and understanding neutrals' role in prominence dynamics. By addressing fundamental mechanisms of energy propagation and exchange in complex plasmas, such as waves, instabilities, and plasma-radiation interactions, the project seeks to consolidate theoretical and numerical computational research in the field. Transitioning from one-dimensional idealized models to multi-dimensional simulations represents a crucial advancement, aligning with the evolving capabilities of solar observation technology.
By the project's conclusion, we significantly advanced our understanding of the processes energizing the partially ionized solar atmosphere. On one hand, we created extensions of multi-fluid theory for arbitrary collisional regimes and developed various computational-numerical tools for realistic modeling of partially ionized plasmas. On the other hand, through the application of these tools, we attained several significant scientific outcomes, detailed below.
We report development of two codes: Mancha3D (single-fluid) and Mancha-2F (two-fluid). Mancha3D features modules for plasma partial ionization, realistic radiative transfer, equation of state, heat conduction, and corona radiative losses, now publicly available. Mancha-2F solves coupled equations for charged and neutral plasma components, with flexible equation sets, elastic and inelastic collisions, viscosity & conductivity.
We made a significant theoretical contribution summarizing the current knowledge of the collisionless fluid models. These models bridge the gap between traditional (MHD) fluid simulations and fully kinetic numerical simulations of the Vlasov equation. We offered a generalization of a highly-collisional Braginskii model. In our formulation, the model is expressed fully analytically through two coupled stress-tensors and two coupled heat fluxes evolution equations for multi-fluid partially ionized plasmas.
We formulated a mode conversion theory for waves in a partially ionized atmosphere. The modified Hall effect provides a new mechanism to couple fast magneto-acoustic and Alfvén waves. Along with the horizontal structuring of the solar atmosphere, this allows for the energy flux of Alfvén waves sufficient for both quiet and active region heating. Magnetic waves are efficiently dissipated through the ambipolar diffusion mechanism or frictional heating, and produce significant plasma-neutral decoupling. Gravitational stratification makes multi-fluid effects influence waves at much low frequencies.
We conducted the first-ever 3D realistic simulations of small-scale dynamo (SSD) and magneto-convection, incorporating partial ionization effects. More intricate SSD fields have a more substantial impact on chromospheric heating through the action of ambipolar and Hall mechanisms than vertically implanted fields. At characteristic times of ~10 minutes for the plasma to become ~500 K hotter at chromospheric locations where ambipolar diffusion is fully resolved in the simulations, with no signs of saturation at our best resolution of 3.5 km. Realistic 3D models of SSD in G, K, and M cool stars demonstrate inherent magnetization of their convection at ~100 G.
We carried out extremely high-resolution multi-fluid simulations of instabilities in cool coronal structures (prominences and coronal rain), fully resolving numerically the physical scales. While we observe a rich variety of multi-fluid effects in these simulations, they become especially prominent at the cool-to-hot plasma transition layers. There, ionization/recombination imbalances create overionized layers with large plasma-neutral drifts (10-20% of the flow speeds), and frictional heating of up to several thousand K, which could potentially be detected in observations.
We participated in defining science cases and instrumentation for the future 4-m EST and first light observing campaigns for DKIST telescopes. High-resolution Mancha3D simulations were used for Adaptive Optics development, and for testing inversion techniques. We undertook a challenging direct detection of plasma-neutral decoupling effects in solar prominences, revealing a slight excess in ion velocities over neutrals.
The knowledge transfer was done by means of communicating our results at multiple conferences and seminars, through collaborations, by organizing the Winter School for the PhD students and young postdocs, by with a series of dedicated workshops on Partially Ionized Plasmas in Astrophysics (PIPA), by mentoring PhD students in our group and those in collaborations.
We made a significant theoretical contribution summarizing the current knowledge of the collisionless fluid models. These models bridge the gap between traditional (MHD) fluid simulations and fully kinetic numerical simulations of the Vlasov equation. We offered a generalization of a highly-collisional Braginskii model. In our formulation, the model is expressed fully analytically through two coupled stress-tensors and two coupled heat fluxes evolution equations for multi-fluid partially ionized plasmas.
We formulated a mode conversion theory for waves in a partially ionized atmosphere. The modified Hall effect provides a new mechanism to couple fast magneto-acoustic and Alfvén waves. Along with the horizontal structuring of the solar atmosphere, this allows for the energy flux of Alfvén waves sufficient for both quiet and active region heating. Magnetic waves are efficiently dissipated through the ambipolar diffusion mechanism or frictional heating, and produce significant plasma-neutral decoupling. Gravitational stratification makes multi-fluid effects influence waves at much low frequencies.
We conducted the first-ever 3D realistic simulations of small-scale dynamo (SSD) and magneto-convection, incorporating partial ionization effects. More intricate SSD fields have a more substantial impact on chromospheric heating through the action of ambipolar and Hall mechanisms than vertically implanted fields. At characteristic times of ~10 minutes for the plasma to become ~500 K hotter at chromospheric locations where ambipolar diffusion is fully resolved in the simulations, with no signs of saturation at our best resolution of 3.5 km. Realistic 3D models of SSD in G, K, and M cool stars demonstrate inherent magnetization of their convection at ~100 G.
We carried out extremely high-resolution multi-fluid simulations of instabilities in cool coronal structures (prominences and coronal rain), fully resolving numerically the physical scales. While we observe a rich variety of multi-fluid effects in these simulations, they become especially prominent at the cool-to-hot plasma transition layers. There, ionization/recombination imbalances create overionized layers with large plasma-neutral drifts (10-20% of the flow speeds), and frictional heating of up to several thousand K, which could potentially be detected in observations.
We participated in defining science cases and instrumentation for the future 4-m EST and first light observing campaigns for DKIST telescopes. High-resolution Mancha3D simulations were used for Adaptive Optics development, and for testing inversion techniques. We undertook a challenging direct detection of plasma-neutral decoupling effects in solar prominences, revealing a slight excess in ion velocities over neutrals.
The knowledge transfer was done by means of communicating our results at multiple conferences and seminars, through collaborations, by organizing the Winter School for the PhD students and young postdocs, by with a series of dedicated workshops on Partially Ionized Plasmas in Astrophysics (PIPA), by mentoring PhD students in our group and those in collaborations.
Our extension of Braginskii models goes significantly beyond the state of the art. Originally from the 1960s, this model represented a cornerstone in plasma transport theory.
Our research unveiled that multi-fluid effects become crucial for waves with frequencies lower than typical interparticle collisional frequencies, unlike suggested by theory of waves in homogeneous plasmas. This discovery carries profound implications, as substantially more energy is available for dissipation at low frequencies.
We showed that ambipolar heating is most significant in the quietest regions, characterized by small-scale dynamo fields. Such a discovery holds profound implications for our comprehension of the formation of the hot chromospheres of the Sun and stars.
We found that multi-fluid effects hold great importance within transition layers between cool and hot materials, such as the solar transition region and prominence-corona interface. Further exploration of these findings is imperative.
Multi-fluid effects operate at scales beyond the resolution capabilities of even our most advanced instrumentation, necessitating specialized observational initiatives. Our initial steps in this direction allowed the detection of subtle differences in velocities between ions and neutrals, aligning with theoretical predictions.
Our research unveiled that multi-fluid effects become crucial for waves with frequencies lower than typical interparticle collisional frequencies, unlike suggested by theory of waves in homogeneous plasmas. This discovery carries profound implications, as substantially more energy is available for dissipation at low frequencies.
We showed that ambipolar heating is most significant in the quietest regions, characterized by small-scale dynamo fields. Such a discovery holds profound implications for our comprehension of the formation of the hot chromospheres of the Sun and stars.
We found that multi-fluid effects hold great importance within transition layers between cool and hot materials, such as the solar transition region and prominence-corona interface. Further exploration of these findings is imperative.
Multi-fluid effects operate at scales beyond the resolution capabilities of even our most advanced instrumentation, necessitating specialized observational initiatives. Our initial steps in this direction allowed the detection of subtle differences in velocities between ions and neutrals, aligning with theoretical predictions.