Retrieving true plasma characteristics from Langmuir probes immersed in the spacecraft sheath: The Double Hemispherical Probe technique.
Abstract
Over the past 50 years Langmuir probes have been widely used for in-situ measurements of ambient plasma in space. However, in situations where the Debye sheath is relatively large (e.g., planetary magnetospheres and solar wind plasma), probes with a limited length have a risk of being engulfed in the sheath of the spacecraft (SC) as indicated in previous missions, causing errors in derived plasma parameters. Here we present a Double Hemispherical Probe (DHP) technique which is able to retrieve true plasma parameters while the probe is engulfed in the SC sheath. The DHP consists of two hemispheres that are installed back-to-back and insulated from each other and swept with a same bias voltage simultaneously. It was shown that the currents of the two hemispheres diverge when the probe is in the deeper sheath. Through laboratory experiments, empirical relationships have been established between the current ratio between the two hemispheres, measured parameters in the sheath, and true ambient plasma parameters. Using these relationships, the retrieved plasma parameters from the DHP measurements in the sheath show good agreement with the true ambient plasma parameters. The DHP technique significantly improves the plasma measurement accuracy and robustness across a wide range of plasma environments.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSH43B..05S
- Keywords:
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- 2494 Instruments and techniques;
- IONOSPHERE;
- 2794 Instruments and techniques;
- MAGNETOSPHERIC PHYSICS;
- 7594 Instruments and techniques;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7894 Instruments and techniques;
- SPACE PLASMA PHYSICS