Contamination effects on fixed-bias Langmuir probes

Abstract

Langmuir probes are standard instruments for plasma density measurements on many sounding rockets. These probes can be operated in swept-bias as well as in fixed-bias modes. In swept-bias Langmuir probes, contamination effects are frequently visible as a hysteresis between consecutive up and down voltage ramps. This hysteresis, if not corrected, leads to poorly determined plasma densities and temperatures. With a properly chosen sweep function, the contamination parameters can be determined from the measurements and correct plasma parameters can then be determined. In this paper, we study the contamination effects on fixed-bias Langmuir probes, where no hysteresis type effect is seen in the data. Even though the contamination is not evident from the measurements, it does affect the plasma density fluctuation spectrum as measured by the fixed-bias Langmuir probe. We model the contamination as a simple resistor-capacitor circuit between the probe surface and the plasma. We find that measurements of small scale plasma fluctuations (meter to sub-meter scale) along a rocket trajectory are not affected, but the measured amplitude of large scale plasma density variation (tens of meters or larger) is attenuated. From the model calculations, we determine amplitude and cross-over frequency of the contamination effect on fixed-bias probes for different contamination parameters. The model results also show that a fixed bias probe operating in the ion-saturation region is affected less by contamination as compared to a fixed bias probe operating in the electron saturation region.

Elevated electron temperatures around twin sporadic E layers at low latitude: Observations and the case for a plausible link to currents parallel to the geomagnetic field

“…Thus, the technique of high spatial resolution density measurements using fixed‒bias Langmuir probe data after normalization to absolute density measurements can be prone to significant errors that are dependent upon the stability of the payload chassis ground relative to the plasma. Note that these errors are in addition to what one might get when the fixed bias probe surface is contaminated [ Steigies and Barjatya , ].…”

Observations of Reduced Turbulence and Wave Activity in the Arctic Middle Atmosphere Following the January 2015 Sudden Stratospheric Warming

“…Each MTeX payload included four plasma density probes. These were a fixed-bias direct current (DC) multi-surface Langmuir probe (mDCP), a sweeping impedance probe (SIP), a sweeping Langmuir probe (SLP), and a multi-needle Langmuir probe (mNLP; Blake, 2014; Blix et al, 1990; Steigies & Barjatya, 2012; Strelnikov et al, 2017). The SIP yielded absolute measurements of the plasma density.…”

Design, Development, Implementation, and On-orbit Performance of the Dynamic Ionosphere CubeSat Experiment Mission

“…However, at DICE spacecraft orbital speeds, the magnitude of ion ram current is significantly higher than the ion thermal current. Generally, with accurate knowledge of the spacecraft speed and the probe ram cross-section area, a LP operating in the ion saturation region can give high resolution absolute ion density measurements, minimize spacecraft charging, and are less susceptible to contamination effects (Steigies and Barjatya 2012). However, for certain conditions of electron temperature, this scenario may have significant errors, thus we will also periodically sweep the LP to determine when DICE is in high electron temperature regimes.…”