Pressure-anisotropy-mediated Helical Dynamo in Turbulent Collisionless Plasmas
The origin of coherent, near-equipartitioned magnetic fields in the universe remains poorly understood, especially in collisionless scenarios. By means of theoretical modeling that includes indispensable kinetic effects and fully kinetic particle-in-cell simulation that contains sufficient scale sep...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal Letters |
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| Online Access: | https://doi.org/10.3847/2041-8213/adaaf5 |
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| author | Z. H. Zhao W. Q. Yuan L. X. Li X. W. Zhu X. X. Jin S. P. Zhu X. T. He B. Qiao |
| author_facet | Z. H. Zhao W. Q. Yuan L. X. Li X. W. Zhu X. X. Jin S. P. Zhu X. T. He B. Qiao |
| author_sort | Z. H. Zhao |
| collection | DOAJ |
| description | The origin of coherent, near-equipartitioned magnetic fields in the universe remains poorly understood, especially in collisionless scenarios. By means of theoretical modeling that includes indispensable kinetic effects and fully kinetic particle-in-cell simulation that contains sufficient scale separation, we self-consistently show that the collisionless large-scale dynamo is quite efficient and the system-scale coherent fields can be generated from kinetic-scale seeds under a turbulent helical drive. We find that, by triggering kinetic mirror and firehose instabilities, the pressure anisotropy—a kinetic effect that is unresolved in conventional magnetohydrodynamics—is the key physics that produces net magnetic helicity that can be inversely transferred to large scales. The magnetic helicity generation rate can be formulated as $\propto {u}_{{\rm{rms}}}^{2}/{L}_{{\rm{in}}}$ , where u _rms is the turbulent velocity and L _in is the driving scale. Our results profoundly refine the picture of cosmic dynamos and potentially resolve the critical issue of dynamo quench. |
| format | Article |
| id | doaj-art-0ebb2e15f2ac4cbc86dc49e34bc33e5b |
| institution | Kabale University |
| issn | 2041-8205 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal Letters |
| spelling | doaj-art-0ebb2e15f2ac4cbc86dc49e34bc33e5b2025-02-01T05:47:10ZengIOP PublishingThe Astrophysical Journal Letters2041-82052025-01-019792L5110.3847/2041-8213/adaaf5Pressure-anisotropy-mediated Helical Dynamo in Turbulent Collisionless PlasmasZ. H. Zhao0https://orcid.org/0000-0003-2051-1740W. Q. Yuan1L. X. Li2X. W. Zhu3X. X. Jin4https://orcid.org/0009-0005-7677-1631S. P. Zhu5X. T. He6B. Qiao7https://orcid.org/0000-0001-9186-8574Center for Applied Physics and Technology, HEDPS and State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University , Beijing 100871, People’s Republic of China ; bqiao@pku.edu.cnCenter for Applied Physics and Technology, HEDPS and State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University , Beijing 100871, People’s Republic of China ; bqiao@pku.edu.cnCenter for Applied Physics and Technology, HEDPS and State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University , Beijing 100871, People’s Republic of China ; bqiao@pku.edu.cnCenter for Applied Physics and Technology, HEDPS and State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University , Beijing 100871, People’s Republic of China ; bqiao@pku.edu.cnCenter for Applied Physics and Technology, HEDPS and State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University , Beijing 100871, People’s Republic of China ; bqiao@pku.edu.cnInstitute of Applied Physics and Computational Mathematics , Beijing 100094, People’s Republic of ChinaCenter for Applied Physics and Technology, HEDPS and State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University , Beijing 100871, People’s Republic of China ; bqiao@pku.edu.cn; Institute of Applied Physics and Computational Mathematics , Beijing 100094, People’s Republic of ChinaCenter for Applied Physics and Technology, HEDPS and State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University , Beijing 100871, People’s Republic of China ; bqiao@pku.edu.cnThe origin of coherent, near-equipartitioned magnetic fields in the universe remains poorly understood, especially in collisionless scenarios. By means of theoretical modeling that includes indispensable kinetic effects and fully kinetic particle-in-cell simulation that contains sufficient scale separation, we self-consistently show that the collisionless large-scale dynamo is quite efficient and the system-scale coherent fields can be generated from kinetic-scale seeds under a turbulent helical drive. We find that, by triggering kinetic mirror and firehose instabilities, the pressure anisotropy—a kinetic effect that is unresolved in conventional magnetohydrodynamics—is the key physics that produces net magnetic helicity that can be inversely transferred to large scales. The magnetic helicity generation rate can be formulated as $\propto {u}_{{\rm{rms}}}^{2}/{L}_{{\rm{in}}}$ , where u _rms is the turbulent velocity and L _in is the driving scale. Our results profoundly refine the picture of cosmic dynamos and potentially resolve the critical issue of dynamo quench.https://doi.org/10.3847/2041-8213/adaaf5Plasma astrophysicsCosmic magnetic fields theoryMagnetic fieldsPlasma physics |
| spellingShingle | Z. H. Zhao W. Q. Yuan L. X. Li X. W. Zhu X. X. Jin S. P. Zhu X. T. He B. Qiao Pressure-anisotropy-mediated Helical Dynamo in Turbulent Collisionless Plasmas The Astrophysical Journal Letters Plasma astrophysics Cosmic magnetic fields theory Magnetic fields Plasma physics |
| title | Pressure-anisotropy-mediated Helical Dynamo in Turbulent Collisionless Plasmas |
| title_full | Pressure-anisotropy-mediated Helical Dynamo in Turbulent Collisionless Plasmas |
| title_fullStr | Pressure-anisotropy-mediated Helical Dynamo in Turbulent Collisionless Plasmas |
| title_full_unstemmed | Pressure-anisotropy-mediated Helical Dynamo in Turbulent Collisionless Plasmas |
| title_short | Pressure-anisotropy-mediated Helical Dynamo in Turbulent Collisionless Plasmas |
| title_sort | pressure anisotropy mediated helical dynamo in turbulent collisionless plasmas |
| topic | Plasma astrophysics Cosmic magnetic fields theory Magnetic fields Plasma physics |
| url | https://doi.org/10.3847/2041-8213/adaaf5 |
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