Electron-scale Kelvin–Helmholtz Instabilities in Magnetized Shear Flows
Electron-scale Kelvin–Helmholtz instabilities (ESKHIs) are found in several astrophysical scenarios. Naturally, ESKHIs are subject to a background magnetic field, but an analytical dispersion relation and an accurate growth rate of ESKHI under this circumstance have remained open because former magn...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ade3cf |
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| Summary: | Electron-scale Kelvin–Helmholtz instabilities (ESKHIs) are found in several astrophysical scenarios. Naturally, ESKHIs are subject to a background magnetic field, but an analytical dispersion relation and an accurate growth rate of ESKHI under this circumstance have remained open because former magnetohydrodynamics derivations are not applicable in the relativistic regime. We present a generalized dispersion relation of ESKHI in relativistic magnetized shear flows, with two-fluid equations in the cold limit. ESKHI linear growth rates in certain cases are numerically calculated. The results show that when the shear velocity is relatively small, the presence of an external magnetic field results in a decreased maximum instability growth rate, a larger cutoff wavenumber of the unstable band, and an increased wavenumber of the most unstable mode. However, when the shear velocity is sufficiently high, the external magnetic field can increase the maximum instability growth rate instead. Particle-in-cell simulations are also carried out to verify our conclusions. In simulations, we observe the generation of a kinetic direct-current (DC) magnetic field, which is shown to have a strong impact on ESKHIs. In the presence of an external magnetic field, the DC magnetic field generation is suppressed because of electron gyration across the shear interface. Beyond the stabilizing threshold external magnetic field predicted by our fluid theory, we further observe possible evidence of Weibel instabilities. |
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| ISSN: | 1538-4357 |