Kinetic Simulations of the interruption of large-amplitude Shear-Alfvén waves in a high-β plasma
Using two-dimensional hybrid-kinetic simulations, we explore the nonlinear "interruption" of standing and traveling shear-Alfvén waves in collisionless plasmas. Interruption involves a self-generated pressure anisotropy removing the restoring force of a linearly polarized Alfvénic perturba...
| Auteurs principaux: | , , , |
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| Format: | Journal article |
| Langue: | English |
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American Physical Society
2017
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| _version_ | 1826291927795892224 |
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| author | Squire, J Kunz, M Quataert, E Schekochihin, A |
| author_facet | Squire, J Kunz, M Quataert, E Schekochihin, A |
| author_sort | Squire, J |
| collection | OXFORD |
| description | Using two-dimensional hybrid-kinetic simulations, we explore the nonlinear "interruption" of standing and traveling shear-Alfvén waves in collisionless plasmas. Interruption involves a self-generated pressure anisotropy removing the restoring force of a linearly polarized Alfvénic perturbation, and occurs for wave amplitudes $δB_{⊥}/B_{0}≳β^{-1/2}$ (where $β$ is the ratio of thermal to magnetic pressure). We use highly elongated domains to obtain maximal scale separation between the wave and the ion gyroscale. For standing waves above the amplitude limit, we find that the large-scale magnetic field of the wave decays rapidly. The dynamics are strongly affected by the excitation of oblique firehose modes, which transition into long-lived parallel fluctuations at the ion gyroscale and cause significant particle scattering. Traveling waves are damped more slowly, but are also influenced by small-scale parallel fluctuations created by the decay of firehose modes. Our results demonstrate that collisionless plasmas cannot support linearly polarized Alfvén waves above $δB_{⊥}/B_{0}∼β^{-1/2}$. They also provide a vivid illustration of two key aspects of low-collisionality plasma dynamics: (i) the importance of velocity-space instabilities in regulating plasma dynamics at high $β$, and (ii) how nonlinear collisionless processes can transfer mechanical energy directly from the largest scales into thermal energy and microscale fluctuations, without the need for a scale-by-scale turbulent cascade. |
| first_indexed | 2024-03-07T03:06:51Z |
| format | Journal article |
| id | oxford-uuid:b2d6e55d-0ddf-4ab8-abe4-0d5a7aad362d |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T03:06:51Z |
| publishDate | 2017 |
| publisher | American Physical Society |
| record_format | dspace |
| spelling | oxford-uuid:b2d6e55d-0ddf-4ab8-abe4-0d5a7aad362d2022-03-27T04:14:34ZKinetic Simulations of the interruption of large-amplitude Shear-Alfvén waves in a high-β plasmaJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:b2d6e55d-0ddf-4ab8-abe4-0d5a7aad362dEnglishSymplectic Elements at OxfordAmerican Physical Society2017Squire, JKunz, MQuataert, ESchekochihin, AUsing two-dimensional hybrid-kinetic simulations, we explore the nonlinear "interruption" of standing and traveling shear-Alfvén waves in collisionless plasmas. Interruption involves a self-generated pressure anisotropy removing the restoring force of a linearly polarized Alfvénic perturbation, and occurs for wave amplitudes $δB_{⊥}/B_{0}≳β^{-1/2}$ (where $β$ is the ratio of thermal to magnetic pressure). We use highly elongated domains to obtain maximal scale separation between the wave and the ion gyroscale. For standing waves above the amplitude limit, we find that the large-scale magnetic field of the wave decays rapidly. The dynamics are strongly affected by the excitation of oblique firehose modes, which transition into long-lived parallel fluctuations at the ion gyroscale and cause significant particle scattering. Traveling waves are damped more slowly, but are also influenced by small-scale parallel fluctuations created by the decay of firehose modes. Our results demonstrate that collisionless plasmas cannot support linearly polarized Alfvén waves above $δB_{⊥}/B_{0}∼β^{-1/2}$. They also provide a vivid illustration of two key aspects of low-collisionality plasma dynamics: (i) the importance of velocity-space instabilities in regulating plasma dynamics at high $β$, and (ii) how nonlinear collisionless processes can transfer mechanical energy directly from the largest scales into thermal energy and microscale fluctuations, without the need for a scale-by-scale turbulent cascade. |
| spellingShingle | Squire, J Kunz, M Quataert, E Schekochihin, A Kinetic Simulations of the interruption of large-amplitude Shear-Alfvén waves in a high-β plasma |
| title | Kinetic Simulations of the interruption of large-amplitude Shear-Alfvén waves in a high-β plasma |
| title_full | Kinetic Simulations of the interruption of large-amplitude Shear-Alfvén waves in a high-β plasma |
| title_fullStr | Kinetic Simulations of the interruption of large-amplitude Shear-Alfvén waves in a high-β plasma |
| title_full_unstemmed | Kinetic Simulations of the interruption of large-amplitude Shear-Alfvén waves in a high-β plasma |
| title_short | Kinetic Simulations of the interruption of large-amplitude Shear-Alfvén waves in a high-β plasma |
| title_sort | kinetic simulations of the interruption of large amplitude shear alfven waves in a high β plasma |
| work_keys_str_mv | AT squirej kineticsimulationsoftheinterruptionoflargeamplitudeshearalfvenwavesinahighbplasma AT kunzm kineticsimulationsoftheinterruptionoflargeamplitudeshearalfvenwavesinahighbplasma AT quataerte kineticsimulationsoftheinterruptionoflargeamplitudeshearalfvenwavesinahighbplasma AT schekochihina kineticsimulationsoftheinterruptionoflargeamplitudeshearalfvenwavesinahighbplasma |