Nonlinear Mirror and Weibel modes: peculiarities of quasi-linear dynamics
A theory for nonlinear evolution of the mirror modes near the instability threshold is developed. It is shown that during initial stage the major instability saturation is provided by the flattening of the velocity distribution function in the vicinity of small parallel ion velocities. The relax...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2010-12-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/28/2161/2010/angeo-28-2161-2010.pdf |
| Summary: | A theory for nonlinear evolution of the mirror modes near
the instability threshold is developed. It is shown that during initial
stage the major instability saturation is provided by the flattening of the
velocity distribution function in the vicinity of small parallel ion
velocities. The relaxation scenario in this case is accompanied by rapid
attenuation of resonant particle interaction which is replaced by a weaker
adiabatic interaction with mirror modes. The saturated plasma state can be
considered as a magnetic counterpart to electrostatic BGK modes. After
quasi-linear saturation a further nonlinear scenario is controlled by the
mode coupling effects and nonlinear variation of the ion Larmor radius. Our
analytical model is verified by relevant numerical simulations. Test
particle and PIC simulations indeed show that it is a modification of
distribution function at small parallel velocities that results in fading
away of free energy driving the mirror mode. The similarity with resonant
Weibel instability is discussed. |
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| ISSN: | 0992-7689 1432-0576 |