Nonlinear growth of firehose and mirror fluctuations in turbulent galaxy-cluster plasmas

TL;DR

This paper investigates how pressure-anisotropy-driven firehose and mirror instabilities grow nonlinearly in turbulent galaxy-cluster plasmas, significantly impacting magnetic field structure and plasma transport.

Contribution

It reveals the nonlinear evolution mechanism of firehose and mirror fluctuations, showing they grow to large amplitudes and influence large-scale plasma dynamics.

Findings

Fluctuations grow to B/B ~ 1 on turbulent timescales.

Small-scale magnetic fluctuations cancel large-scale magnetic field changes.

Impacts on plasma transport and large-scale dynamics are significant.

Abstract

In turbulent high-beta astrophysical plasmas (exemplified by the galaxy cluster plasmas), pressure-anisotropy-driven firehose and mirror fluctuations grow nonlinearly to large amplitudes, dB/B ~ 1, on a timescale comparable to the turnover time of the turbulent motions. The principle of their nonlinear evolution is to generate secularly growing small-scale magnetic fluctuations that on average cancel the temporal change in the large-scale magnetic field responsible for the pressure anisotropies. The presence of small-scale magnetic fluctuations may dramatically affect the transport properties and, thereby, the large-scale dynamics of the high-beta astrophysical plasmas.