DUST CHARGES, CLOUD POTENTIAL, AND INSTABILITIES IN A DUST CLOUD EMBEDDED IN A PLASMA
DUST CHARGES, CLOUD POTENTIAL, AND INSTABILITIES IN A DUST CLOUD EMBEDDED IN A PLASMA
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DOI：
10.1029/ja092ia03p02281
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发表时间：
1987-03-01
影响因子：
2.8
通讯作者：
IP, W
中科院分区：
文献类型：
--
作者：
HAVNES, O;GOERTZ, CK;IP, W
我们考虑嵌入无限等离子体中的有限大小的尘埃云。尘埃云的电势通常与周围等离子体的电势不同，并且进入尘埃云的粒子会加速或减速。我们处理两种极限情况：在情况 A 中，粒子在云内没有热化，在情况 B 中，等离子体在云内部热化，形成麦克斯韦等离子体，其密度由玻尔兹曼关系式给出，作为局部云势的函数。定性地讲，这两种情况都会产生相似的结果：在稀薄的云中，尘埃云电势较低，而尘埃电势接近单个孤立尘埃颗粒的电势。在稠密的尘埃云中，云势接近最大值，而尘埃势随着尘埃密度的增加而降低至零。然而，对于同一组其他云和环境等离子体参数，这两种情况下电势的精确值可能有很大差异。另外，对于情况 A，我们可能对这两个电势有几组解决方案，所有这些都提供云中的电荷平衡和灰尘的电流平衡。然而，我们发现，对于所有范围的灰尘密度来说，情况 A 可能不容易形成，因为灰尘的充电可能需要比散射过程更长的时间才能导致两种等离子体粒子类型的内部玻尔兹曼分布。另一方面，我们期望介于情况 A 和情况 B 之间的半稳定情况能够找到多种解决方案。通过创建双层和两种解决方案之间的过渡可能会出现不稳定性，并导致尘埃云中的事件。我们认为此类事件可能发生在彗星彗发和行星环中，并导致尘埃云结构的变化。在速度空间中与扩散的散射碰撞将等离子体速度分布转变为情况 B 之前，与多个解相关的条件可能会相当短暂，最多 10 天几次。在这种情况下，每组云和等离子体参数的势只有一个解。
We consider a finite‐sized dust cloud embedded in an infinite plasma. The dust cloud will generally be at a different potential from that of the ambient plasma, and particles which enter the cloud are accelerated or decelerated. We treat the two limiting cases: in case A, particles are not thermalized within the cloud, and in case B, the plasma is thermalized in the cloud interior to form a Maxwellian plasma with densities given by Boltzmann relations as functions of the local cloud potential. Qualitatively, both cases lead to similar results: In a tenuous cloud the dust cloud potential is low while the dust potentials are close to those of single isolated dust particles. In dense dust clouds the cloud potential approaches a maximum while the dust potentials decreases to zero with increasing dust density. However, the exact values of the potentials can differ considerably for the two cases for the same set of other cloud and ambient plasma parameters. Also, for case A we may have several sets of solutions for the two potentials, all giving charge balance in the cloud and current balance to the dust. We find, however, that case A may not easily be formed for all ranges of dust densities because the charging of dust can take a longer time than the time for scattering processes to lead to internal Boltzmann distributions for both plasma particle types. On the other hand, we expect semistable cases intermediate between case A and case B with multiple solutions to be found. Instabilities through the creation of double layers and transitions between two solutions may occur and lead to events in dust clouds. We suggest that such events may possibly occur in cometary comas and in planetary rings and lead to changes in the dust cloud structure. Conditions relevant for multiple solutions will probably be rather short‐lived, at most a few times 10 days, before scattering collisions with diffusion in velocity space turn the plasma velocity distribution into that of case B. In this case there is only one solution for the potentials for each set of cloud and plasma parameters.