Fluidization of collisionless plasma turbulence
In a collisionless, magnetized plasma, particles may stream freely along magnetic field lines, leading to “phase mixing” of their distribution function and consequently, to smoothing out of any “compressive” fluctuations (of density, pressure, etc.). This rapid mixing underlies Landau damping of the...
| Main Authors: | , , , |
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| Format: | Journal article |
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National Academy of Sciences
2019
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| _version_ | 1826261420769017856 |
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| author | Meyrand, R Kanekar, A Dorland, W Schekochihin, A |
| author_facet | Meyrand, R Kanekar, A Dorland, W Schekochihin, A |
| author_sort | Meyrand, R |
| collection | OXFORD |
| description | In a collisionless, magnetized plasma, particles may stream freely along magnetic field lines, leading to “phase mixing” of their distribution function and consequently, to smoothing out of any “compressive” fluctuations (of density, pressure, etc.). This rapid mixing underlies Landau damping of these fluctuations in a quiescent plasma—one of the most fundamental physical phenomena that makes plasma different from a conventional fluid. Nevertheless, broad power law spectra of compressive fluctuations are observed in turbulent astrophysical plasmas (most vividly, in the solar wind) under conditions conducive to strong Landau damping. Elsewhere in nature, such spectra are normally associated with fluid turbulence, where energy cannot be dissipated in the inertial-scale range and is, therefore, cascaded from large scales to small. By direct numerical simulations and theoretical arguments, it is shown here that turbulence of compressive fluctuations in collisionless plasmas strongly resembles one in a collisional fluid and does have broad power law spectra. This “fluidization” of collisionless plasmas occurs, because phase mixing is strongly suppressed on average by “stochastic echoes,” arising due to nonlinear advection of the particle distribution by turbulent motions. Other than resolving the long-standing puzzle of observed compressive fluctuations in the solar wind, our results suggest a conceptual shift for understanding kinetic plasma turbulence generally: rather than being a system where Landau damping plays the role of dissipation, a collisionless plasma is effectively dissipationless, except at very small scales. The universality of “fluid” turbulence physics is thus reaffirmed even for a kinetic, collisionless system. |
| first_indexed | 2024-03-06T19:21:10Z |
| format | Journal article |
| id | oxford-uuid:1a226aba-1de3-4061-bd9e-eab9a9934883 |
| institution | University of Oxford |
| last_indexed | 2024-03-06T19:21:10Z |
| publishDate | 2019 |
| publisher | National Academy of Sciences |
| record_format | dspace |
| spelling | oxford-uuid:1a226aba-1de3-4061-bd9e-eab9a99348832022-03-26T10:53:06ZFluidization of collisionless plasma turbulenceJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:1a226aba-1de3-4061-bd9e-eab9a9934883Symplectic Elements at OxfordNational Academy of Sciences2019Meyrand, RKanekar, ADorland, WSchekochihin, AIn a collisionless, magnetized plasma, particles may stream freely along magnetic field lines, leading to “phase mixing” of their distribution function and consequently, to smoothing out of any “compressive” fluctuations (of density, pressure, etc.). This rapid mixing underlies Landau damping of these fluctuations in a quiescent plasma—one of the most fundamental physical phenomena that makes plasma different from a conventional fluid. Nevertheless, broad power law spectra of compressive fluctuations are observed in turbulent astrophysical plasmas (most vividly, in the solar wind) under conditions conducive to strong Landau damping. Elsewhere in nature, such spectra are normally associated with fluid turbulence, where energy cannot be dissipated in the inertial-scale range and is, therefore, cascaded from large scales to small. By direct numerical simulations and theoretical arguments, it is shown here that turbulence of compressive fluctuations in collisionless plasmas strongly resembles one in a collisional fluid and does have broad power law spectra. This “fluidization” of collisionless plasmas occurs, because phase mixing is strongly suppressed on average by “stochastic echoes,” arising due to nonlinear advection of the particle distribution by turbulent motions. Other than resolving the long-standing puzzle of observed compressive fluctuations in the solar wind, our results suggest a conceptual shift for understanding kinetic plasma turbulence generally: rather than being a system where Landau damping plays the role of dissipation, a collisionless plasma is effectively dissipationless, except at very small scales. The universality of “fluid” turbulence physics is thus reaffirmed even for a kinetic, collisionless system. |
| spellingShingle | Meyrand, R Kanekar, A Dorland, W Schekochihin, A Fluidization of collisionless plasma turbulence |
| title | Fluidization of collisionless plasma turbulence |
| title_full | Fluidization of collisionless plasma turbulence |
| title_fullStr | Fluidization of collisionless plasma turbulence |
| title_full_unstemmed | Fluidization of collisionless plasma turbulence |
| title_short | Fluidization of collisionless plasma turbulence |
| title_sort | fluidization of collisionless plasma turbulence |
| work_keys_str_mv | AT meyrandr fluidizationofcollisionlessplasmaturbulence AT kanekara fluidizationofcollisionlessplasmaturbulence AT dorlandw fluidizationofcollisionlessplasmaturbulence AT schekochihina fluidizationofcollisionlessplasmaturbulence |