New Theory and Applications with the Regularized Kappa-Distribution

• Applicant: Privatdozent Dr. Horst Fichtner
• Subject Area: Astrophysics and Astronomy
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 511321267

With this project we will advance the non-equilibrium plasma theory and corresponding specific applications by employing the Regularized Kappa Distribution (RKD) that was introduced recently for a realistic treatment and interpretation of suprathermal particle populations and their implications in various astrophysical systems. This RKD allows one to overcome a series of critical limitations and deficiencies of the standard Kappa distribution (SKD) mainly determined by the diverging velocity moments, a non-extensive entropy as well as undesired contributions of unphysical superluminal particles. The new RKD concept motivates systematic explorations of its consequences in kinetic as well as fluid theory and corresponding studies of astrophysical plasma systems on small and large scales. Consequently, the main objective of the proposed project is to develop new theoretical approaches based on the RKD and to apply them to non-equilibrium multi-scale plasmas, with an emphasis on the best observed astrophysical system, i.e., the heliosphere. This objective is explicitly formulated with two scientific key questions, one of which is addressing kinetic theory and the other the fluid theory: (Q1) What are the implications of using the RKD in the kinetic theory for the properties of plasma waves and instabilities? (Q2) How can a fluid theory based on the RKD be derived and applied to nonthermal astrophysical systems? The answer to the first question will clarify, by means of analytical and numerical modelling, the consequences of using the RKD for plasma waves on small, i.e. kinetic scales. That to the second question will establish a consistent quantitative treatment of the plasma dynamics on large, i.e. fluid scales. The modelling and its assessment with data will be realized by the fulfillment of the following three tasks: (i) the development of the kinetic theory for the RKD and its application to particle populations in the solar wind plasma, (ii) the use of macroscopic moments of the RKD and appropriate source terms for mass, momentum and energy to derive MHD-like fluid equations and their application, and (iii) the validation of the kinetic and fluid results with spacecraft data. With the corresponding analytical and numerical studies we will not only deepen the understanding of the physical relevance of the RKD and its significance for astrophysical plasma systems, in particular the solar wind, but also establish, for the first time, a kinetic and a fluid description of nonthermal astrophysical plasmas that are fully consistent with each other. The validation of the theory and the modelling will be made on the basis of various spacecraft data, particularly from the recently launched NASA mission Parker Solar Probe and the forthcoming ESA mission Solar Orbiter.

• DFG Programme: Research Grants
• International Connection: Belgium, Brazil, Finland, France
• Partner Organisation: Fonds Wetenschappelijk Onderzoek - Vlaanderen ; Research Foundation Flanders (FWO)
• Cooperation Partners: Professor Dr. Rudi Gaelzer; Professor Dr. Milan Maksimovic; Professor Dr. Stefaan Poedts; Dr. Jens Aarre Vilhelm Pomoell