Means to remove electrode contamination effect of Langmuir probe measurement in space

Abstract

Precaution to remove the serious effect of electrode contamination in Langmuir probe experiments has not been taken in many space measurements because the effect is either not understood or ignored. We stress here that one should pay extra attention to the electrode contamination effect to get accurate and reliable plasma measurements so that the long time effort for sounding rocket/satellite missions does not end in vain or becomes less fruitful. In this paper, we describe two main features of voltage-current characteristic curves associated with the contaminated Langmuir probe, which are predicted from the equivalent circuit model, which we proposed in 1970's. We then show that fast sweeping dc Langmuir probes can give reliable results in the steady state regime. The fast sweeping probe can also give reliable results in transient situations such as satellite moves through plasma bubble in the ionosphere where the electron density drastically changes. This fact was first confirmed in our laboratory experiment.

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

“…Figure b presents two consecutive SLP sweeps from 390 km. The lack of any significant hysteresis, in both the lower altitude and the higher altitude sweeps, can be attributed to the internally heated probe [ Amatucci et al , ] as well as fast 25 Hz sweeping [ Oyama , ; Oyama et al , ]. Heating is expected to remove the contamination and the fast sweeping is expected to short circuit the contamination capacitance.…”

The Multi-Needle Langmuir Probe System on Board NorSat-1

“…The work by Oyama et al [2012] experimentally conrmed that if the probe bias is swept fast enough, i.e., at several Hz, the hysteresis can be removed and accurate plasma parameters can be derived from the obtained I-V curve. We carried out the sweep test with our fabricated cylindrical probe (25 mm length and 0.51 mm diameter).…”

DC Langmuir Probe for Measurement of Space Plasma: A Brief Review

“…Accordingly, T e is expected to be nearly equal to T n . We know that most of the measurements provided in 1970 are not correct (Oyama et al 1980) mainly due to electrode contamination (Oyama 1976;Oyama et al 2012). However, even when an electrode with a clean surface is used (Hirao & Oyama 1972;Oyama & Hirao 1976;Oyama et al 2008a, b) or another instrument is used whose measurement is not influenced by electrode contamination, the measurements still show T e to be higher than T n during the daytime.…”