Electron cyclotron harmonic (ECH) waves play a significant role in driving the diffuse aurora, which constitutes more than 75% of the particle energy input into the ionosphere. ECH waves in magnetospheric plasmas have long been thought to be excited predominantly by the loss cone anisotropy (velocity–space gradients) that arises naturally in a planetary dipole field. Recent THEMIS observations, however, indicate that an electron beam can also excite such waves in Earth's magnetotail. The ambient and beam plasma conditions under which electron beam excitation can take place are unknown. Knowledge of such conditions would allow us to further explore the relative contribution of this excitation mechanism to ECH wave scattering of magnetospheric electrons at Earth and the outer planets. Using the hot plasma dispersion relation, we address the nature of beam-driven ECH waves and conduct a comprehensive parametric survey of this instability. We find that growth is provided by beam electron cyclotron resonances of both first and higher orders. We also find that these waves are unstable under a wide range of plasma conditions. The growth rate increases with beam density, beam velocity, and hot electron temperature; it decreases with increasing beam temperature and beam temperature anisotropy ($T_{\perp }/T_{\parallel }$), hot electron density, and cold electron density and temperature. Such conditions abound in Earth's magnetotail, where magnetospheric electrons heated by earthward convection and magnetic reconnection coexist with colder ionospheric electrons.

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光束驱动的 ECH 波：参数研究

电子回旋谐波 (ECH) 波在驱动漫射极光方面发挥着重要作用，它构成了输入到电离层的粒子能量的 75% 以上。长期以来，一直认为磁层等离子体中的 ECH 波主要由行星偶极子场中自然产生的损耗锥各向异性（速度-空间梯度）激发。然而，最近的 THEMIS 观测表明，电子束也可以激发地球磁尾中的这种波。可以发生电子束激发的环境和束等离子体条件是未知的。了解这些条件将使我们能够进一步探索这种激发机制对地球和外行星磁层电子 ECH 波散射的相对贡献。使用热等离子体色散关系，我们解决了光束驱动 ECH 波的性质，并对这种不稳定性进行了全面的参数调查。我们发现增长是由一阶和更高阶的束电子回旋共振提供的。我们还发现这些波在广泛的等离子体条件下是不稳定的。生长速率随着束密度、束速和热电子温度而增加；它随着光束温度和光束温度各向异性的增加而降低（${吨}_{\perp }/{吨}_{\parallel }$)、热电子密度、冷电子密度和温度。这种情况在地球的磁尾中比比皆是，在那里，被地球对流和磁重联加热的磁层电子与较冷的电离层电子共存。