Quasi-linear approach of bi-Kappa distributed electrons with dynamic $κ$ parameter. EMEC instability
Fuente:
arXiv
Saved in:
| Main Authors: | , , , , , |
|---|---|
| Format: | Preprint |
| Published: |
2026
|
| Subjects: | |
| Online Access: | |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1866912834843049984 |
|---|---|
| author | Moya, Pablo S Navarro, Roberto E Lazar, Marian Yoon, Peter H López, Rodrigo A Poedts, Stefaan |
| author_facet | Moya, Pablo S Navarro, Roberto E Lazar, Marian Yoon, Peter H López, Rodrigo A Poedts, Stefaan |
| contents | In recent years, significant progress has been made in the velocity-moment-based quasi-linear (QL) theory of waves and instabilities in plasmas with nonequilibrium velocity distributions (VDs) of the Kappa (or $κ$) type. However, the temporal variation of the parameter $κ$, which quantifies the presence of suprathermal particles, is not fully captured by such a QL analysis, and typically $κ$ remains constant during plasma dynamics. We propose a new QL modeling that goes beyond the limits of a previous approach, realistically assuming that the quasithermal core cannot evolve independently of energetic suprathermals. The case study is done on the electron-cyclotron (EMEC) instability generated by anisotropic bi-Kappa electrons with $A=T_\perp/T_\parallel > 1$ ($\parallel, \perp$ denoting directions with respect to the background magnetic field). The parameter $κ$ self-consistently varies through the QL equation of kurtosis (fourth-order moment) coupled with temporal variations of the temperature components, relaxing the constraint on the independence of the low-energy (core) electrons and suprathermal high-energy tails of VDs. The results refine and extend previous approaches. A clear distinction is made between regimes that lead to a decrease or an increase in the $κ$ parameter with saturation of the instability. What predominates is a decrease in $κ$, i.e., an excess of suprathermalization, which energizes suprathermal electrons due to self-generated wave fluctuations. Additionally, we found that VDs can evolve toward a quasi-Maxwellian shape (as $κ$ increases) primarily in regimes with low beta and initial kappa values greater than five. Instability-driven relaxation only partially resolves temperature anisotropy in bi-Kappa electron VDs, as wave fluctuations generally act to further energize suprathermal electrons. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_13888 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Quasi-linear approach of bi-Kappa distributed electrons with dynamic $κ$ parameter. EMEC instability Moya, Pablo S Navarro, Roberto E Lazar, Marian Yoon, Peter H López, Rodrigo A Poedts, Stefaan Plasma Physics Solar and Stellar Astrophysics In recent years, significant progress has been made in the velocity-moment-based quasi-linear (QL) theory of waves and instabilities in plasmas with nonequilibrium velocity distributions (VDs) of the Kappa (or $κ$) type. However, the temporal variation of the parameter $κ$, which quantifies the presence of suprathermal particles, is not fully captured by such a QL analysis, and typically $κ$ remains constant during plasma dynamics. We propose a new QL modeling that goes beyond the limits of a previous approach, realistically assuming that the quasithermal core cannot evolve independently of energetic suprathermals. The case study is done on the electron-cyclotron (EMEC) instability generated by anisotropic bi-Kappa electrons with $A=T_\perp/T_\parallel > 1$ ($\parallel, \perp$ denoting directions with respect to the background magnetic field). The parameter $κ$ self-consistently varies through the QL equation of kurtosis (fourth-order moment) coupled with temporal variations of the temperature components, relaxing the constraint on the independence of the low-energy (core) electrons and suprathermal high-energy tails of VDs. The results refine and extend previous approaches. A clear distinction is made between regimes that lead to a decrease or an increase in the $κ$ parameter with saturation of the instability. What predominates is a decrease in $κ$, i.e., an excess of suprathermalization, which energizes suprathermal electrons due to self-generated wave fluctuations. Additionally, we found that VDs can evolve toward a quasi-Maxwellian shape (as $κ$ increases) primarily in regimes with low beta and initial kappa values greater than five. Instability-driven relaxation only partially resolves temperature anisotropy in bi-Kappa electron VDs, as wave fluctuations generally act to further energize suprathermal electrons. |
| title | Quasi-linear approach of bi-Kappa distributed electrons with dynamic $κ$ parameter. EMEC instability |
| topic | Plasma Physics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2601.13888 |