Magnetofluid dynamics of magnetized cosmic plasma: firehose and gyrothermal instabilities
Both global dynamics and turbulence in magnetized weakly collisional cosmic plasmas are described by general magnetofluid equations that contain pressure anisotropies and heat fluxes that must be calculated from microscopic plasma kinetic theory. It is shown that even without a detailed calculation...
| Main Authors: | , , , |
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| פורמט: | Journal article |
| שפה: | English |
| יצא לאור: |
2009
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| _version_ | 1826285845879980032 |
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| author | Schekochihin, A Cowley, S Rincon, F Rosin, MS |
| author_facet | Schekochihin, A Cowley, S Rincon, F Rosin, MS |
| author_sort | Schekochihin, A |
| collection | OXFORD |
| description | Both global dynamics and turbulence in magnetized weakly collisional cosmic plasmas are described by general magnetofluid equations that contain pressure anisotropies and heat fluxes that must be calculated from microscopic plasma kinetic theory. It is shown that even without a detailed calculation of the pressure anisotropy or the heat fluxes, one finds the macroscale dynamics to be generically unstable to microscale Alfvenically polarized fluctuations. Two instabilities are considered in detail: the parallel firehose instability (including the finite-Larmor-radius effects that determine the fastest growing mode) and the gyrothermal instability (GTI). The latter is a new result - it is shown that a parallel ion heat flux destabilizes Alfvenically polarized fluctuations even in the absence of the negative pressure anisotropy required for the firehose. The main conclusion is that both pressure anisotropies and heat fluxes trigger plasma microinstabilities and, therefore, their values will likely be set by the nonlinear evolution of these instabilities. Ideas for understanding this nonlinear evolution are discussed. It is argued that cosmic plasmas will generically be "three-scale systems," comprising global dynamics, mesoscale turbulence and microscale plasma fluctuations. The astrophysical example of cool cores of galaxy clusters is considered and it is noted that observations point to turbulence in clusters being in a marginal state with respect to plasma microinstabilities and so it is the plasma microphysics that is likely to set the heating and conduction properties of the intracluster medium. In particular, a lower bound on the scale of temperature fluctuations implied by the GTI is derived. |
| first_indexed | 2024-03-07T01:34:57Z |
| format | Journal article |
| id | oxford-uuid:94d94082-4b78-4cf2-8a72-1b8deaee42b4 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T01:34:57Z |
| publishDate | 2009 |
| record_format | dspace |
| spelling | oxford-uuid:94d94082-4b78-4cf2-8a72-1b8deaee42b42022-03-26T23:42:10ZMagnetofluid dynamics of magnetized cosmic plasma: firehose and gyrothermal instabilitiesJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:94d94082-4b78-4cf2-8a72-1b8deaee42b4EnglishSymplectic Elements at Oxford2009Schekochihin, ACowley, SRincon, FRosin, MSBoth global dynamics and turbulence in magnetized weakly collisional cosmic plasmas are described by general magnetofluid equations that contain pressure anisotropies and heat fluxes that must be calculated from microscopic plasma kinetic theory. It is shown that even without a detailed calculation of the pressure anisotropy or the heat fluxes, one finds the macroscale dynamics to be generically unstable to microscale Alfvenically polarized fluctuations. Two instabilities are considered in detail: the parallel firehose instability (including the finite-Larmor-radius effects that determine the fastest growing mode) and the gyrothermal instability (GTI). The latter is a new result - it is shown that a parallel ion heat flux destabilizes Alfvenically polarized fluctuations even in the absence of the negative pressure anisotropy required for the firehose. The main conclusion is that both pressure anisotropies and heat fluxes trigger plasma microinstabilities and, therefore, their values will likely be set by the nonlinear evolution of these instabilities. Ideas for understanding this nonlinear evolution are discussed. It is argued that cosmic plasmas will generically be "three-scale systems," comprising global dynamics, mesoscale turbulence and microscale plasma fluctuations. The astrophysical example of cool cores of galaxy clusters is considered and it is noted that observations point to turbulence in clusters being in a marginal state with respect to plasma microinstabilities and so it is the plasma microphysics that is likely to set the heating and conduction properties of the intracluster medium. In particular, a lower bound on the scale of temperature fluctuations implied by the GTI is derived. |
| spellingShingle | Schekochihin, A Cowley, S Rincon, F Rosin, MS Magnetofluid dynamics of magnetized cosmic plasma: firehose and gyrothermal instabilities |
| title | Magnetofluid dynamics of magnetized cosmic plasma: firehose and
gyrothermal instabilities |
| title_full | Magnetofluid dynamics of magnetized cosmic plasma: firehose and
gyrothermal instabilities |
| title_fullStr | Magnetofluid dynamics of magnetized cosmic plasma: firehose and
gyrothermal instabilities |
| title_full_unstemmed | Magnetofluid dynamics of magnetized cosmic plasma: firehose and
gyrothermal instabilities |
| title_short | Magnetofluid dynamics of magnetized cosmic plasma: firehose and
gyrothermal instabilities |
| title_sort | magnetofluid dynamics of magnetized cosmic plasma firehose and gyrothermal instabilities |
| work_keys_str_mv | AT schekochihina magnetofluiddynamicsofmagnetizedcosmicplasmafirehoseandgyrothermalinstabilities AT cowleys magnetofluiddynamicsofmagnetizedcosmicplasmafirehoseandgyrothermalinstabilities AT rinconf magnetofluiddynamicsofmagnetizedcosmicplasmafirehoseandgyrothermalinstabilities AT rosinms magnetofluiddynamicsofmagnetizedcosmicplasmafirehoseandgyrothermalinstabilities |