Retrieving True Plasma Characteristics from Langmuir Probes Immersed in the Spacecraft Sheath: The Double Hemispherical Probe Technique

Abstract

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 boom length have a risk of being engulfed by 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 identify whether the probe is in the SC sheath and retrieve true plasma parameters. The DHP consists of two hemispheres that are installed back-to-back and electrically isolated from each other. The two hemispheres are swept with the same bias voltage simultaneously. It is shown that the currents of the two hemispheres diverge when the probe is in the sheath. Through laboratory experiments, empirical relationships are established between the current ratio of the two hemispheres, measured parameters in the sheath, and true ambient plasma parameters. Using these relationships, the plasma parameters retrieved from the DHP measurements in the sheath show good agreement with the true ambient plasma parameters. The DHP technique significantly improves the measurement accuracy across a wide range of plasma environments.

A Double Hemispherical Probe for Characterizing and Minimizing the Self‐Wake Effects on Probe Measurements

“…The current ratio I e 1 / I e 2 in the electron saturation region was found to be a constant value, similar to that shown by Samaniego and Wang (2019). I e 1 / I e 2 is plotted as a function of R D in Figure 4a.…”

“…In low‐density plasmas (Case i), probes can be engulfed in the Debye sheath of SC, causing measurement errors. The DHP has been shown to be able to identify such situation and retrieve the true ambient plasma characteristics from probe measurements in the SC sheath (Samaniego & Wang, 2019). Here this paper is to address Case ii—flowing plasmas in which a self‐wake is created behind the probe itself.…”

“…In this paper, we continue the development of the DHP technology (Samaniego & Wang, 2019; Wang et al, 2018) to address the probe self‐wake effects on probe measurements, especially for the electron population. The outline of this paper is as follows.…”

New procedure to estimate plasma parameters through the q-Weibull distribution by using a Langmuir probe in a cold plasma

“…In spite of the limitations mentioned, we consider that the q-Weibull distribution has enough flexibility to be used in different contexts, as is shown in many applications that have similar EEPFs compared to the ones we present in this work, for example in plasma space [70,6,71], plasma fusion [72], dusty plasmas [73] and cold plasma physics [74,75,76,77,78,79] in general. We expect that the q and r parameters can be useful to determine the plasma operating regimes and the discharge zones, and to measure the degree of departure of the system from the Maxwellian distribution.…”

The Regular Features Recorded by the Langmuir Probe Onboard the Low Earth Polar Orbit Satellite CSES

“…The Langmuir probe has been used as an effective tool for in‐situ plasma parameter measurements since the past century (Bering et al., 1973; Mott‐Smith & Langmuir, 1926; Samaniego & Wang, 2019). In recent decades, it has been widely carried by many Low Earth Orbit (LEO) satellites, such as the Challenging Minisatellite Payload (CHAMP) (Cooke et al., 2003), the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) (Lebreton et al., 2006), the Swarm satellites (Alpha, Bravo, and Charlie) (Buchert et al., 2015), and the China Seismo‐Electromagnetic Satellite (CSES) (Shen et al., 2018) whose Langmuir probe data is the subject of this paper.…”