Modeling of current characteristics of segmented Langmuir probe on DEMETER

Abstract

International audienceWe model the current characteristics of the DEMETER Segmented Langmuir probe (SLP). The probe is used to measure electron density and temperature in the ionosphere at an altitude of approximately 700 km. It is also used to measure the plasma flow velocity in the satellite frame of reference. The probe is partitioned into seven collectors: six electrically insulated spherical segments and a guard electrode (the rest of the sphere and the small post). Comparisons are made between the predictions of the model and DEMETER measurements for actual ionospheric plasma conditions encountered along the satellite orbit. Segment characteristics are computed numerically with PTetra, a three-dimensional particle in cell simulation code. In PTetra, space is discretized with an unstructured tetrahedral mesh, thus, enabling a good representation of the probe geometry. The model also accounts for several physical effects of importance in the interaction of spacecraft with the space environment. These include satellite charging, photoelectron, and secondary electron emissions. The model is electrostatic, but it accounts for the presence of a uniform background magnetic field. PTetra simulation results show different characteristics for the different probe segments. The current collected by each segment depends on its orientation with respect to the ram direction, the plasma composition, the magnitude, and the orientation of the magnetic field. It is observed that the presence of light H þ ions leads to a significant increase in the ion current branch of the I-V curves of the negatively polarized SLP. The effect of the magnetic field is demonstrated by varying its magnitude and direction with respect to the reference magnetic field. It is found that the magnetic field appreciably affects the electron current branch of the I-V curves of certain segments on the SLP, whereas the ion current branch remains almost unaffected. PTetra simulations are validated by comparing the computed characteristics and their angular anisotropy with the DEMETER measurements, as simulation results are found to be in good agreement with the measurements. V C 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4804336

Development of a Double Hemispherical Probe for Improved Space Plasma Measurements

“…The probe was a sphere that consisted of seven segments, including six disc‐shaped small segments distributed around the probe and the rest of the sphere serving as the guard. The anisotropy in the ion current collected by different segments was used to characterize the velocity vector of the ion flow (Imtiaz et al, ). The dual SLPs were also flown on ESA's PROBA2 mission (Santandrea et al, ).…”

Accelerated Steady-State Electrostatic Particle-in-Cell Simulation of Langmuir Probes

“…For example, collisions can significantly affect ion current to Langmuir probes (e.g., Schulz & Brown 1955;Sternovsky & Robertson 2002;Sternovsky et al 2003;Sudit & Woods 1994;Zakrzewski & Kopiczynski 1974), and a number of studies have used PIC codes with Monte Carlo collision capabilities to study this, using 1D cylindrical or spherical models (with 3D velocities) and a Boltzmann electron distribution (Taccogna et al 2004;Tejero-del-Caz et al 2016;Voloshin et al 2015) or fully kinetic electrons (Cenian et al 2005;Iza & Lee 2006;Soberón 2006;Trunec et al 2015;Zikán et al 2019), including surface effects such as secondary electron emission (Cenian et al 2014). PIC has been critical in simulating Langmuir probes with asymmetric 3D geometries (Chiaretta 2011;Hilgers et al 2008;Hruby & Hrach 2010;Imtiaz et al 2013;Podolník et al 2018;Séran et al 2005), and has been used for probe and sheath analysis in the presence of magnetic fields (Bergmann 2002;Podolník et al 2018). The effect of nonuniform plasma and flowing plasma conditions are other examples ripe for exploration with PIC (Imtiaz et al 2013;Knappmiller & Robertson 2007;Olson et al 2010;Séran et al 2005).…”

“…PIC has been critical in simulating Langmuir probes with asymmetric 3D geometries (Chiaretta 2011;Hilgers et al 2008;Hruby & Hrach 2010;Imtiaz et al 2013;Podolník et al 2018;Séran et al 2005), and has been used for probe and sheath analysis in the presence of magnetic fields (Bergmann 2002;Podolník et al 2018). The effect of nonuniform plasma and flowing plasma conditions are other examples ripe for exploration with PIC (Imtiaz et al 2013;Knappmiller & Robertson 2007;Olson et al 2010;Séran et al 2005). When Langmuir probe measurements are complicated by effects such as described above, I(V ) cannot often be precisely predicted analytically; simulations can predict I(V ), but solving the inverse problem-finding the n 0 , T e , T i that yield a simulated I(V ) closest to the measured I(V )-is extremely expensive, computationally.…”

“…The techniques presented in this paper could speed Langmuir probe simulation by two orders of magnitude, which makes the inverse problem much more feasible. Many of the above-mentioned studies could have benefited significantly from the techniques described in this paper; only a few took advantage of numerical timestepping (Hilgers et al 2008;Imtiaz et al 2013;Séran et al 2005).…”

A First Assessment of a Regression-Based Interpretation of Langmuir Probe Measurements

“…With present computing facilities, an interesting alternative would be to use detailed three-dimensional kinetic simulations capable of accounting for all the relevant physical processes under realistic geometry conditions. Kinetic simulations have been, and continue to be, applied to specific case studies and elucidate selected processes [8][9][10] but, due to the considerable computational resources and run times that they require, they cannot be used in real-time interpretation of probe measurements. An approach is proposed here to process low level L1B data from probe measurements (current as a function of voltage) into higher level L2 data (density, temperature, floating potential, ...) from kinetic simulations.…”