在寒冷环境和土卫二尘埃中纳米颗粒的电荷
On the charge of nanograins in cold environments and Enceladus dust
摘要：
在极低能量的等离子体中，纳米颗粒的尺寸与两个电子的相互作用能等于它们的热能的距离（所谓的朗道长度）相当。在这种情况下，接近带电粒子引起的颗粒极化增加了它们的通量，并减少了充电时间尺度。此外，对于半径小于朗道长度的晶粒，电荷不再随尺寸线性减小，而是具有接近于一个电子电荷的最可几平衡值。我们给出的分析结果，可用于外太阳系的冷密行星环境中的纳米颗粒。应用于在土星卫星土卫二的羽流中观察到的纳米尘埃表明，大多数半径约为1 nm的颗粒应该携带一个电子，而其中相当大的一部分由于离子撞击而带正电。相应的静电应力会破坏较小的晶粒，这些晶粒无论如何可能不作为晶体存在，因为它们的分子数量接近结晶所需的最小值。
英文摘要：
In very-low energy plasmas, the size of nanograins is comparable to the distance (the so-called Landau length) at which the interaction energy of two electrons equals their thermal energy. In that case, the grain's polarization induced by approaching charged particles increases their fluxes and reduces the charging time scales. Furthermore, for grains of radius smaller than the Landau length, the electric charge no longer decreases linearly with size, but has a most probable equilibrium value close to one electron charge. We give analytical results that can be used for nanograins in cold dense planetary environments of the outer solar system. Application to the nanodust observed in the plume of Saturn's moon Enceladus shows that most grains of radius about 1 nm should carry one electron, whereas an appreciable fraction of them are positively charged by ion impacts. The corresponding electrostatic stresses should destroy smaller grains, which anyway may not exist as crystals since their number of molecules is close to the minimum required for crystallization.
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