标题： 太阳风超热电子的消防水管约束 显示英文标题

标题： Firehose constraints for the solar wind suprathermal electrons

摘要： 太阳风沿行星际磁场方向平行扩展所预测的温度不定增加已经因未能被观测证实而广为人知。 在高温稀薄的太空等离子体中，粒子间的碰撞对于限制偏离各向同性的大幅变化效率不高，但由此产生的火 hose 不稳定性在这种情况下为电子和质子两种物种的热（核心）群体的温度各向异性提供了合理的限制。 本文讨论了在太阳风中普遍存在的超热（晕层）电子。 密度较低但比核心更热的超热电子可能具有高度各向异性和易受火 hose 不稳定性影响的特点。 这里的火 hose 不稳定性主要特征是从专门针对太阳风中超热电子以及地球磁层条件的初步理论推导而来。 在此揭示的新火 hose 不稳定性状态可能完全由超热电子控制。 研究发现，超热电子系统性地激发了火 hose 不稳定性，并且其阈值接近观测到的温度各向异性极限。 这些结果为火 hose 不稳定性在空间等离子体温度各向异性松弛中的作用提供了新的且有价值的确凿证据。 显示英文摘要

摘要： The indefinite increase of temperature predicted by the solar wind expansion in the direction parallel to the interplanetary magnetic field is already notorious for not being confirmed by the observations. In hot and dilute plasmas from space particle-particle collisions are not efficient in constraining large deviations from isotropy, but the resulting firehose instability provides in this case plausible limitations for the temperature anisotropy of the thermal (core) populations of both the electron and proton species. The present paper takes into discussion the suprathermal (halo) electrons, which are ubiquitous in the solar wind. Less dense but hotter than the core, suprathermals may be highly anisotropic and susceptible to the firehose instability. The main features of the instability are here derived from a first-order theory for conditions specific to the suprathermal electrons in the solar wind and terrestrial magnetospheres. Unveiled here, new regimes of the electron firehose instability may be exclusively controlled by the suprathermals. The instability is found to be systematically stimulated by the suprathermal electrons, with thresholds that approach the limits of the temperature anisotropy reported by the observations. These results represent new and valuable evidences for the implication of the firehose instability in the relaxation of the temperature anisotropy in space plasmas.