Space‐borne Langmuir probes generally have a self‐wake behind themselves due to supersonic relative velocities (Mach number M > 1) between the spacecraft and ambient plasma ions. Such a wake may create difficulties for correctly measuring plasma characteristics. Here we present a new technique—the Double Hemispherical Probe (DHP) to characterize and minimize the self‐wake effects on probe measurements. The DHP consists of two hemispheres that are simultaneously swept with a bias voltage to obtain two independent current‐voltage (I‐V) curves, which are used to identify the wake effects of the probe. A laboratory DHP model is inserted in plasma flows (M > 10) created in the Colorado Solar Wind Experiment (CSWE) chamber. In this case, the ion current is the ram current collected by the upstream hemisphere of the DHP, leaving an ion wake behind the downstream hemisphere. A wide range of the Debye ratio R_D (ratio of the probe radius to electron Debye length) is tested, and it is found that (1) when R_D < 1, the electron currents collected by the two hemispheres are similar, indicating a uniform electron density around the probe, and (2) when R_D > 1, the electron current collected by the downstream hemisphere becomes lower than the upstream, indicating a reduced electron density in the probe's wake due to the ambipolar electric field effect. In this case, the electron density measured by traditional single Langmuir probes will be underestimated. With the DHP, we can use the upstream hemisphere measurements to minimize the self‐wake effects.

中文翻译：

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双半球形探头，用于表征和最小化探头测量的自唤醒效应

由于航天器和周围等离子体离子之间的超音速相对速度（马赫数M > 1），星载Langmuir探测器通常会自唤醒。这样的唤醒可能会导致难以正确测量等离子体特性。在这里，我们介绍了一种新技术-双半球形探头（DHP），以表征并最小化对探头测量的自唤醒影响。DHP由两个半球组成，这些半球同时用偏置电压扫描，以获得两条独立的电流-电压（IV）曲线，这些曲线用于识别探头的唤醒效应。将实验室DHP模型插入血浆流（M> 10）在科罗拉多州太阳风实验（CSWE）室中创建。在这种情况下，离子电流是DHP上游半球收集的冲压电流，而离子流则在下游半球后面。测试了大范围的德拜比R _D（探针半径与电子德拜长度的比），发现（1）当R _D <1时，两个半球收集的电子电流相似，表明探针周围均匀的电子密度，以及（2）当R _D> 1时，下游半球收集的电子电流变得低于上游半球，这表明由于双极性电场效应，探针尾流中的电子密度降低。在这种情况下，传统的朗缪尔探针测得的电子密度将被低估。借助DHP，我们可以使用上游半球测量来最大程度地减少自唤醒效应。