Mutual Impedance Probe in Collisionless Unmagnetized Plasmas With Suprathermal Electrons—Application to BepiColombo

Context: Mutual impedance experiments are active electric probes providing in-situ space plasma measurements. Such active experiments consist of a set of electric antennas used as transmitter(s) and receivers(s) through which various dielectric properties of the plasma can be probed, giving therefore access to key plasma parameters such as, for instance, the electron density or the electron temperature. Since the beginning of the space exploration, such active probes have been launched and operated in Earth's ionospheric and magnetospheric plasmas. More recently and in the coming years, mutual impedance probes have been and will be operated onboard exploratory planetary missions, such as Rosetta, BepiColombo and JUICE, to probe the cometary plasma of 67P/Churyumov-Gerasimenko, the Hermean and the Jovian magnetospheres, respectively.Aims: Some analytic modeling is necessary to calibrate and analyse mutual impedance observations in order to access to macroscopic bulk plasma quantities. In situ particle observations from various space missions have confirmed that space plasmas are out of local thermodynamic equilibrium. This means that particle velocity distributions can be far from a Maxwellian distribution, exhibiting for instance temperature anisotropies, beams or a suprathermal population. The goal of this paper is to characterize the effect of suprathermal electrons on the instrumental response in order to assess the robustness of plasma diagnostics based on mutual impedance measurements in plasmas characterized by a significant amount of suprathermal particles.Methods: The instrumental response directly depends on the electron velocity distribution function (evdf). In this work, we choose to model suprathermal electrons by considering different approaches using: (i) a kappa evdf, (ii) a double-Maxwellian evdf or (iii) a mix of a Maxwellian evdf and a kappa evdf. For each case, we compute the spatial distribution of the electrostatic potential induced by the transmitters, discretized and modeled here as an ensemble of pulsating point charges.Results: We apply our modeling by building synthetic mutual impedance spectra of the PWI/AM2P probe, lauched in October 2018 onboard the Mercury Magnetospheric Orbiter (MIO/MMO) spacecraft of the BepiColombo exploratory space mission, in order to calibrate and analyse the future electron observations in the plasma environment of Mercury

Testing the Ampère-Maxwell law on the photon mass and Lorentz-Poincaré symmetry violation with MMS multi-spacecraft data

International audienceThe photon is commonly believed being the only free massless particle. Deviations from the Ampère-Maxwell law, due to a photon mass, real for the de Broglie-Proca theory, or effective for the Lorentz-Poincaré Symmetry Violation (LSV) in the Standard-Model Extension (SME) were sought in six years of MMS satellite data. In a minority of cases, out of which $76\%$ in modulus and $65\%$ in Cartesian components for the highest time resolution burst data and best tetrahedron configurations in the solar wind and peripheries, deviations have been found. After currents error analysis, the minimal photon mass would be $1.74 \times 10^{-53}$ kg while the minimal LSV parameter $|\vec{k}^{\rm AF}|$ value would be $4.95 \times 10^{-11}$ m$^{-1}$. These values are compared with actual limits and discussed

Observations of mixed warm and cold electrons with RPC-MIP at comet 67P/Churyumov-Gerasimenko

International audienceIn the ionosphere of the comet 67P/Churyumov-Gerasimenko, the Rosetta Plasma Consortium (RPC) instruments have been measuring the plasma environment during more than two years from August 2014 to September 2016. The Ion Electron Sensor (RPC-IES) and the Langmuir Probes (RPC-LAP) onboard the Rosetta orbiter reported different electron populations: (i) a suprathermal electron component (40-100 eV), (ii) a warm electron component of cometary origin (5-10 eV) and (iii) a cold component (<1 eV) of electrons thermalized by collisions with neutrals. The Mutual Impedance Probe (RPC-MIP) has been operated to measure the total electron density. Gilet et al. (2017) simulated the mutual impedance response for a probe immerged in a two-electron temperature plasma, with both cold and warm component modelled by a Maxwellian distribution. Through a direct comparison between simulated and measured mutual impedance spectra, the density and the temperature of the two electron populations have been retrieved. This study focuses on three events: (i) on 2015 November 1st in the magnetized cometary plasma near perihelion (1.4 AU), (ii) inside a diamagnetic (unmagnetized) region on 2015 November 20, still near perihelion, and (iii) far from perihelion (3.2 AU) on 2016 May 23. We illustrate the dynamics of the cold and warm electron populations and show that cold electrons can be transported along the magnetic field far from the electron-neutral collision dominated region where electrons are expected to have cooled down

Radiations at Twice the Solar-Wind Plasma Frequency Upstream of the Earth's Bow Shock.

Radiations at twice the plasma frequency, Fpe, have been commonly observed in the foreshock regions upstream of the Earth's bow shock and far beyond. These electromagnetic radiations are thought to be produced in the electron foreshock and most probably close to the interplanetary magnetic field line tangent to the shock surface. They are often seen simultaneously with suprathermal electrons that are energized at the shock and are backstreaming from it. The objective of the current presentation is to show and discuss 2Fpe radiation events recorded onboard the four CLUSTER spacecraft by the WHISPER relaxation sounder

Observations of mixed warm and cold electrons with RPC-MIP at comet 67P/Churyumov-Gerasimenko

International audiencePredicted by numerical simulations, the Mutual Impedance Probe (RPC-MIP) onboard the ESA's Rosetta spacecraft observed signatures of a mixed warm and cold electron population in the cometary plasma of 67P/Churuymov-Gerasimenko. Thanks to the high cadence measurements of the RPC-MIP instrument, we illustrate the dynamics of the cold and warm electron populations. We confirm the observations of the cold component provided by the Langmuir Probes (RPC-LAP). The electron density and the electron temperature are consistent with RPC-LAP

Observations of mixed warm and cold electrons with RPC-MIP at comet 67P/Churyumov-Gerasimenko

International audienceIn the ionosphere of the comet 67P/Churyumov-Gerasimenko, the Rosetta Plasma Consortium (RPC) instruments have been measuring the plasma environment during more than two years from August 2014 to September 2016. The Ion Electron Sensor (RPC-IES) and the Langmuir Probes (RPC-LAP) onboard the Rosetta orbiter reported different electron populations: (i) a suprathermal electron component (40-100 eV), (ii) a warm electron component of cometary origin (5-10 eV) and (iii) a cold component (<1 eV) of electrons thermalized by collisions with neutrals. The Mutual Impedance Probe (RPC-MIP) has been operated to measure the total electron density. Gilet et al. (2017) simulated the mutual impedance response for a probe immerged in a two-electron temperature plasma, with both cold and warm component modelled by a Maxwellian distribution. Through a direct comparison between simulated and measured mutual impedance spectra, the density and the temperature of the two electron populations have been retrieved. This study focuses on three events: (i) on 2015 November 1st in the magnetized cometary plasma near perihelion (1.4 AU), (ii) inside a diamagnetic (unmagnetized) region on 2015 November 20, still near perihelion, and (iii) far from perihelion (3.2 AU) on 2016 May 23. We illustrate the dynamics of the cold and warm electron populations and show that cold electrons can be transported along the magnetic field far from the electron-neutral collision dominated region where electrons are expected to have cooled down

Analytic theory of Titan's Schumann resonance: Constraints on ionospheric conductivity and buried water ocean

International audienceThis study presents an approximate model for the atypical Schumann resonance in Titan's atmosphere that accounts for the observations of electromagnetic waves and the measurements of atmospheric conductivity performed with the HASI-PWA (Huygens Atmospheric Structure and Permittivity, Wave and Altimetry) instrumentation during the descent of the Huygens Probe through Titan's atmosphere in January 2005. After many years of thorough analyses of the collected data, several arguments enable us to claim that the Extremely Low Frequency (ELF) wave observed at around 36 Hz displays all the characteristics of the second harmonic of a Schumann resonance. On Earth, this phenomenon is well known to be triggered by lightning activity. Given the lack of evidence of any thunderstorm activity on Titan, we proposed in early works a model based on an alternative powering mechanism involving the electric current sheets induced in Titan's ionosphere by the Saturn's magnetospheric plasma flow. The present study is a further step in improving the initial model and corroborating our preliminary assessments. We first develop an analytic theory of the guided modes that appear to be the most suitable for sustaining Schumann resonances in Titan's atmosphere. We then introduce the characteristics of the Huygens electric field measurements in the equations, in order to constrain the physical parameters of the resonating cavity. The latter is assumed to be made of different structures distributed between an upper boundary, presumably made of a succession of thin ionized layers of stratospheric aerosols spread up to 150 km and a lower quasi-perfect conductive surface hidden beneath the non-conductive ground. The inner reflecting boundary is proposed to be a buried water-ammonia ocean lying at a likely depth of 55 - 80 km below a dielectric icy crust. Such estimate is found to comply with models suggesting that the internal heat could be transferred upwards by thermal conduction of the crust, while convective processes cannot be ruled out

Observations of mixed warm and cold electrons with RPC-MIP at comet 67P/Churyumov-Gerasimenko

International audiencePredicted by numerical simulations, the Mutual Impedance Probe (RPC-MIP) onboard the ESA's Rosetta spacecraft observed signatures of a mixed warm and cold electron population in the cometary plasma of 67P/Churuymov-Gerasimenko. Thanks to the high cadence measurements of the RPC-MIP instrument, we illustrate the dynamics of the cold and warm electron populations. We confirm the observations of the cold component provided by the Langmuir Probes (RPC-LAP). The electron density and the electron temperature are consistent with RPC-LAP

Observations of cold electrons by RPC-MIP at 67P/Churuymov-Gerasimenko

International audienceThe Mutual Impedance Probe (MIP) of the Rosetta Plasma Consortium (RPC) onboard the Rosetta orbiter operated during more than two years from August 2014 to September 2016 in order to measure the electron density in the cometary ionosphere of 67P/Churyumov-Gerasimenko. This experiment is based on the resonance of plasma eigenmodes to detect the electron plasma frequency, itself directly related to the electron density. Recent models of mutual impedance probes [1,2] showed that in a two-electron temperature plasma, a double-resonance can be visible on mutual impedance spectra. This characteristic has been observed in-situ within the RPC-MIP data during the post-perihelion operation at all heliocentric distances (from 1.3 to 3.8 AU), corroborated the measurement of a mix of two electron populations done independently by the Langmuir Probes (RPC-LAP) [3,4,5]. For this study, we investigated the RPC-MIP dataset containing the characteristics of a mix of two electron populations in order to characterize the colder population observed by RPC-MIP during the cometary mission. We show that the observation of cold electrons strongly depends on the latitude. Indeed, in the southern hemisphere of 67P, where the neutral outgassing activity was higher than in northern hemisphere during post-perihelion, the cold electrons were more presents which confirms the cooling of the electrons by the cometary neutrals. We also show that the cold electrons are mainly observed outside the electron-neutral collision dominated region (exobase) where electrons are expected to have cooled down which supposed that the cold electrons have been transported. Finally, RPC-MIP measured cold electrons far from the perihelion where the neutral outgassing activity is lower, which suggest that the collisional electron cooling is more efficient than previously expected. [1] Gilet, N., Henri, P., Wattieaux, G., Cilibrasi, M., & Béghin, C., 2017, Radio Science, 52, 1432 [2] Wattieaux, G., Gilet, N., Henri, P., Vallières, X., & Bucciantini, L., submitted in A&A [3] Eriksson, A. I., Engelhardt, I. A., André, M., et al., 2017, A&A, 605, A15 [4] Engelhardt, I. A. D., Eriksson, A. I., Vigren, E., et al., 2018, A&A, 616, A51 [5] Odelstad, E., Eriksson, A. I., Johansson, F. L., et al., 2018, JGR, 123,

Observations of cold electrons by RPC-MIP at 67P/Churuymov-Gerasimenko

International audienceThe Mutual Impedance Probe (MIP) of the Rosetta Plasma Consortium (RPC) onboard the Rosetta orbiter operated during more than two years from August 2014 to September 2016 in order to measure the electron density in the cometary ionosphere of 67P/Churyumov-Gerasimenko. This experiment is based on the resonance of plasma eigenmodes to detect the electron plasma frequency, itself directly related to the electron density. Recent models of mutual impedance probes [1,2] showed that in a two-electron temperature plasma, a double-resonance can be visible on mutual impedance spectra. This characteristic has been observed in-situ within the RPC-MIP data during the post-perihelion operation at all heliocentric distances (from 1.3 to 3.8 AU), corroborated the measurement of a mix of two electron populations done independently by the Langmuir Probes (RPC-LAP) [3,4,5]. For this study, we investigated the RPC-MIP dataset containing the characteristics of a mix of two electron populations in order to characterize the colder population observed by RPC-MIP during the cometary mission. We show that the observation of cold electrons strongly depends on the latitude. Indeed, in the southern hemisphere of 67P, where the neutral outgassing activity was higher than in northern hemisphere during post-perihelion, the cold electrons were more presents which confirms the cooling of the electrons by the cometary neutrals. We also show that the cold electrons are mainly observed outside the electron-neutral collision dominated region (exobase) where electrons are expected to have cooled down which supposed that the cold electrons have been transported. Finally, RPC-MIP measured cold electrons far from the perihelion where the neutral outgassing activity is lower, which suggest that the collisional electron cooling is more efficient than previously expected. [1] Gilet, N., Henri, P., Wattieaux, G., Cilibrasi, M., & Béghin, C., 2017, Radio Science, 52, 1432 [2] Wattieaux, G., Gilet, N., Henri, P., Vallières, X., & Bucciantini, L., submitted in A&A [3] Eriksson, A. I., Engelhardt, I. A., André, M., et al., 2017, A&A, 605, A15 [4] Engelhardt, I. A. D., Eriksson, A. I., Vigren, E., et al., 2018, A&A, 616, A51 [5] Odelstad, E., Eriksson, A. I., Johansson, F. L., et al., 2018, JGR, 123,