Relative drifts between different species or particle populations are characteristic to solar plasma outflows, e.g., in the fast streams of the solar winds, coronal mass ejections and interplanetary shocks. This paper characterizes the dispersion and stability of the low-beta alpha/proton drifts in the absence of any intrinsic thermal anisotropies, which are usually invoked in order to stimulate various instabilities. The dispersion relations derived here describe the full spectrum of instabilities and their variations with the angle of propagation and plasma parameters. The results unveil a potential competition between instabilities of the electromagnetic proton cyclotron and alpha cyclotron modes. For conditions specific to a low-beta solar wind, e.g., at low heliocentric distances in the outer corona, the instability operates on the alpha cyclotron branch. The growth rates of the alpha cyclotron mode are systematically stimulated by the (parallel) plasma beta and/or the alpha-proton temperature ratio. One can therefore expect that this instability develops even in the absence of temperature anisotropies, with potential to contribute to a self-consistent regulation of the observed drift of alpha particles.

中文翻译：

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空间等离子体中低βα/质子束的电磁不稳定性

不同物种或粒子群之间的相对漂移是太阳等离子体流出的特征，例如，在太阳风的快速流、日冕物质抛射和行星际冲击中。本文描述了在不存在任何固有热各向异性的情况下低 β α/质子漂移的分散和稳定性，这通常被调用以激发各种不稳定性。这里导出的色散关系描述了不稳定性的全谱及其随传播角度和等离子体参数的变化。结果揭示了电磁质子回旋加速器模式和阿尔法回旋加速器模式的不稳定性之间的潜在竞争。对于特定于低β太阳风的条件，例如，在外日冕的低日心距离下，不稳定性作用于阿尔法回旋加速器分支。α 回旋加速器模式的生长速率受到（平行）等离子体β 和/或α-质子温度比的系统刺激。因此可以预期，即使在没有温度各向异性的情况下，这种不稳定性也会发展，有可能有助于对观察到的 α 粒子漂移进行自洽调节。