Using analytical theory and hybrid-kinetic numerical simulations, we demonstrate that, in a collisionless plasma, long-wavelength ion-acoustic waves (IAWs) with amplitudes $\delta n/n_0 \gtrsim 2/\beta$ (where $\beta \gg {1}$ is the ratio of thermal to magnetic pressure) generate sufficient pressure anisotropy to destabilize the plasma to firehose and mirror instabilities. These kinetic instabilities grow rapidly to reduce the pressure anisotropy by pitch-angle scattering and trapping particles, respectively, thereby impeding the maintenance of Landau resonances that enable such waves’ otherwise potent collisionless damping. The result is wave dynamics that evince a weakly collisional plasma: the ion distribution function is near-Maxwellian, the field-parallel flow of heat resembles its Braginskii form (except in regions where large-amplitude magnetic mirrors strongly suppress particle transport), and the relations between various thermodynamic quantities are more ‘fluid-like’ than kinetic. A nonlinear fluctuation–dissipation relation for self-sustaining IAWs is obtained by solving a plasma-kinetic Langevin problem, which demonstrates suppressed damping, enhanced fluctuation levels and weakly collisional thermodynamics when IAWs with $\delta n/n_0 \gtrsim 2/\beta$ are stochastically driven. We investigate how our results depend upon the scale separation between the wavelength of the IAW and the Larmor radius of the ions, and discuss briefly their implications for our understanding of turbulence and transport in the solar wind and the intracluster medium of galaxy clusters.

中文翻译：

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无碰撞、高 β 等离子体中的自持声音

使用解析理论和混合动力学数值模拟，我们证明，在无碰撞等离子体中，具有振幅的长波长离子声波 (IAW) $\delta n/n_0 \gtrsim 2/\beta$ （在哪里 $\beta \gg {1}$ 是热压与磁压之比）产生足够的压力各向异性以使等离子体不稳定，从而产生消防水带和镜面不稳定性。这些动力学不稳定性迅速增长，分别通过俯仰角散射和捕获粒子来降低压力各向异性，从而阻碍了朗道共振的维持，而朗道共振使这种波能够具有其他有效的无碰撞阻尼。结果是显示弱碰撞等离子体的波动力学：离子分布函数接近麦克斯韦，热的场平行流动类似于其 Braginskii 形式（大振幅磁镜强烈抑制粒子传输的区域除外），并且各种热力学量之间的关系更像是“流体”而不是动力学。 $\delta n/n_0 \gtrsim 2/\beta$ 是随机驱动的。我们研究了我们的结果如何依赖于 IAW 的波长和离子的拉莫尔半径之间的尺度分离，并简要讨论了它们对我们理解太阳风和星系团的团内介质中的湍流和传输的影响。