Abstract
An effect of the bi-Maxwellian counterstreaming distribution function is analyzed with regard to the linear low frequency instabilities in magnetized homogeneous collisionless plasmas. New analytical marginal instability conditions for the firehose and the mirror modes have been obtained. Presence of counterstreams along the ambient magnetic field causes a huge effect on the instability conditions of those modes. The instability conditions very sensitively depend on the functional dependence of the counterstreaming parameter P. The theoretically predicted results might give a full potential explanation for the observed solar wind temperature anisotropy diagram in A-β∥ plane [S. D. Bale et al., Phys. Rev. Lett. 103, 211101 (2009)].
Highlights
The theory of linear kinetic instabilities in homogeneous magnetized plasmas has a long lasting history
There has been a good understanding of linear kinetic instabilities in plasmas with a bi-Maxwellian or a kappa distribution function, which is represented in variety of analytical and numerical studies
The present paper focuses on identifying the marginal instability conditions of the low frequency magnetosonic modes in bi-Maxwellian counterstreaming plasmas
Summary
The theory of linear kinetic instabilities in homogeneous magnetized plasmas has a long lasting history. The marginal instability condition for the O-mode (as well as for low frequency magnetosonic modes47) is given only in terms of the temperature anisotropy A and parallel plasma beta bk, and the theoretical predictions can be directly transferred to the A-bk plane and compared with the observations.. Some data analyses are available with regard to the Alfven speed and the parallel plasma beta of the solar wind, it seems to be not enough, since those analyses represent only separate statistics on VA and bk, but not their changes with respect to each other Another way to compare the predicted instability conditions of the bi-Maxwellian counterstreaming model with the observations will become possible, if in contrast to the representation of the observed solar wind data in A-bk plane, other representations (in A-VA or A-uk plane) are available.
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