Kinetic Modeling of Langmuir Probes in Space and Application to the MAVEN Langmuir Probe and Waves Instrument. Issue 3 (22nd March 2021)

• Record Type: Journal Article
• Authors: Ergun, R. E.; Andersson, L. A.; Fowler, C. M.; Thaller, S. A.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 3(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-22
• Subjects: Electron density -- electron temperature -- Langmuir probe -- Mars ionosphere -- MAVEN; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2020JA028956
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Self‐consistent kinetic solutions from test‐particle simulations are used to improve the derivation of electron temperature ( T e ) and density ( n e ) from Langmuir probes in space. While Langmuir probes are well understood, the non‐ideal characteristics of space‐flight instruments can influence the accuracy of T e and n e and how they are derived. In particular, when in an ionosphere, spacecraft motion often causes a sensor wake and exposes its surface to oxidation. This work has two primary goals. We present kinetic solutions of general interest then apply our findings to the Langmuir Probe and Waves (LPW) instrument on the MAVEN satellite. Of general interest, (1) kinetic solutions show that mechanical mounting of a Langmuir probe sensor and controlling the potential of nearby surfaces is critical for accuracy. (2) An ion wake generated by the sensor can greatly modify how n e must be derived. (3) Interestingly, small voltage variations on the surface of the sensor do not significantly diminish the accuracy of T e and n e . (4) On the other hand, surface resistance on the sensor can appreciably disturb the derivation of T e . The LPW instrument is recalibrated with the aid of kinetic solutions and published results from laboratory experiments. The systematic uncertainty (as opposed to random variations) in T e is improved to as low as ±0.005 eV (±60 K) when n e > ∼3 × 10 4 cm −3 . This recalibration leads to some of the most accurate measurements of T e made in space and can result in improved modeling of Mars' ionosphere. Key Points: Self‐consistent kinetic solutions reveal that a sensor wake can alter the I ‐ V characteristic of a Langmuir probe The measurement accuracy of T e by the MAVEN Langmuir Probe and Waves instrument is dramatically improved from kinetic modeling Self‐consistent kinetic solutions from a test‐particle simulation improve the accuracy of the electron density measurement