Hollow cathode plasma contactors have an extensive history as spacecraft neutralizers, but questions remain on whether the technology can neutralize significant positive charging in tenuous space plasmas. Simulations and a representative semianalytical model (which we term the ion emission model) predict effective neutralization in these scenarios as ion current is emitted from the surface of the quasi-neutral contactor plasma according to the space-charge limit. This article focuses on experimental plasma measurements of a hollow cathode biased to several positive voltages with respect to a surrounding vacuum chamber in order to validate the ion emission model. Particular attention is paid to the emitted ions (those reaching the chamber wall) and to the ion-rich sheath region where the ion emission process takes place. Retarding potential analyzer (RPA) measurements were performed to understand ion flow velocity and direction as these parameters relate directly to the current predicted by the ion emission model. Planar probe measurements were performed at the chamber wall to compare local emission currents to model predictions. Evidence of collisions within the plasma (particularly charge exchange collisions) and simple models predicting ion energetics are presented. These experiments suggest that ion emission from the contactor plasma acts according to the ion emission model and adds to the physical understanding of spacecraft neutralization using hollow cathode plasma contactors as it may occur in tenuous space plasmas.

中文翻译：

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正偏置空心阴极等离子体的离子发射

空心阴极等离子体接触器作为航天器中和器有着悠久的历史，但该技术是否可以中和微弱空间等离子体中的显着正电荷仍存在疑问。模拟和代表性的半分析模型（我们称之为离子发射模型）预测在这些情况下有效中和，因为根据空间电荷限制，离子电流从准中性接触器等离子体的表面发射。本文重点介绍相对于周围真空室偏置到几个正电压的空心阴极的实验等离子体测量，以验证离子发射模型。特别注意发射的离子（那些到达腔壁的离子）和离子发射过程发生的富含离子的鞘区。执行延迟电位分析仪 (RPA) 测量以了解离子流动速度和方向，因为这些参数与离子发射模型预测的电流直接相关。在腔壁处进行平面探针测量，以将局部发射电流与模型预测进行比较。介绍了等离子体内碰撞的证据（特别是电荷交换碰撞）和预测离子能量学的简单模型。这些实验表明，接触器等离子体的离子发射根据离子发射模型起作用，并增加了对使用空心阴极等离子体接触器的航天器中和的物理理解，因为它可能发生在稀薄的空间等离子体中。