http://arxiv.org/abs/2011.10504
Turbulence in space plasmas usually exhibits two distinct regimes separated by a spectral break that divides the inertial and kinetic ranges in which wave-wave or wave-particle interactions dominate, respectively. Large scale fluctuations are dominated by MHD non-linear wave-wave interactions following a -5/3 or -3/2 slope power-law spectrum, that suddenly ends and after the break the spectrum follows a steeper power-law $k^{-\alpha}$ shape given by a spectral index $\alpha > 5/3$. Despite its ubiquitousness, few research have considered the possible effects of a turbulent background spectrum in the quasilinear relaxation of solar wind temperatures. In this work, a quasilinear kinetic theory is used to study the evolution of the proton temperatures in a solar wind-like plasma composed by cold electrons and bi-Maxwellian protons, in which electromagnetic waves propagate along a background magnetic field. Four wave spectrum shapes are compared with different levels of wave intensity. We show that a sufficient turbulent magnetic power can drive stable protons to transverse heating, resulting in an increase in the temperature anisotropy and the reduction of the parallel proton beta. Thus, stable proton velocity distribution can evolve in such a way as to develop kinetic instabilities. This may explain why the constituents of the solar wind can be observed far from thermodynamic equilibrium and near the instability thresholds.
P. Moya and R. Navarro
Mon, 23 Nov 20
51/63
Comments: 13 pages, 5 figures, submitted to Frontiers in Physics
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