Improved Determination of Plasma Density Based on Spacecraft Potential of the Magnetospheric Multiscale Mission Under Active Potential Control
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Data from the Magnetospheric Multiscale (MMS) mission, in particular, the spacecraft potential measured with and without the ion beams of the active spacecraft potential control (ASPOC) instruments, plasma electron moments, and the electric field, have been employed for an improved determination of plasma density based on spacecraft potential. The known technique to derive plasma density from spacecraft potential sees the spacecraft behaving as a plasma probe which adopts a potential at which the ambient plasma current and one of photoelectrons produced at the surface and leaving into space are in equilibrium. Thus, the potential is a function of the plasma current, and plasma density can be determined using measurements or assumptions on plasma temperature. This method is especially useful during periods when the plasma instruments are not in operation or when spacecraft potential data have significantly higher time resolution than particle detectors. However, the applicable current-voltage characteristic of the spacecraft has to be known with high accuracy, particularly when the potential is actively controlled and shows only minor residual variations. This paper demonstrates recent refinements of the density determination coming from: 1) the reduction of artifacts in the potential data due to the geometry of the spinning spacecraft and due to effects of the ambient electric field on the potential measurements and 2) a calibration of the plasma current to the spacecraft surfaces which is only possible by comparison with the variable currents from the ion beams of ASPOC. The results are discussed, and plasma densities determined by this method are shown in comparison with measurements by the Fast Plasma Instrument (FPI) for some intervals of the MMS mission.Keywords:
Spacecraft charging
Astrophysical plasma
Scientific satellites immersed in various space environments are surrounded by plasmas which they are supposed to analyze, using instruments such as particle detectors. The presence of these structures within the plasma leads to a variety of complex and inter-correlated spacecraft/plasma interactions. The space plasma modifies the satellite which in return disturbs its close environment. On-board instruments measure a perturbed plasma and it is difficult to distinguish the natural signal from biased measurements. The objective of this thesis is to study and improve the understanding of the spacecraft/plasma interactions, through numerical simulations performed with the SPIS software, on the low energy domain (<100 eV), as those particles are the most perturbed. The aim is to understand plasma measurements on realistic cases, by establishing a methodology of simulating those issues. I simulate interactions between the Solar Probe Plus, Solar Orbiter, Cluster missions and their respective environments, including the associated measurements. The analysis of the obtained results allows the understanding of the various cases and the validation of the methodology developed during this work.
Spacecraft charging
Orbiter
Astrophysical plasma
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Plasma measurements by electrostatic probes are influenced by the spacecraft-plasma interaction, including the photoelectrons emitted by the spacecraft. Such effects get particularly important in tenuous plasmas with large Debye lengths. We have used the particle-in-cell code package SPIS to study the close environment of the Rosetta spacecraft, and the impact of the spacecraft-plasma interaction on the electrostatic potential at the position of the Langmuir probes onboard. The simulations show that in the solar wind, photoemission has a bigger impact than wake formation. Spacecraft potential estimates based on Langmuir probe data in the solar wind need to be compensated for these effects when the spacecraft attitude varies. The SPIS simulations are validated by comparison to an independent code.
Spacecraft charging
Langmuir Probe
Astrophysical plasma
Particle-in-cell
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Space development has been rapidly increasing, and a strong demand should arise regarding the understanding of the spacecraft-plasma interactions, which is one of the very important issues associated with the human activities in space. To evaluate the spacecraft-plasma interactions including plasma kinetics, transient process, and electromagnetic field variation, the authors have started to develop a numerical plasma chamber called Geospace Environment Simulator (GES) by making the most use of the conventional full particle-in-cell plasma simulations. For the development of a proto model of GES, the authors have used the Earth Simulator, which is one of the fastest supercomputers in the world. GES can be regarded as a numerical chamber in which space experiments can be virtually performed and temporal and spatial evolutions of spacecraft-plasma interactions can be analyzed. In this paper, the authors have briefly introduced GES in terms of its concept, modeling, and research targets. As one of the research topics of GES, the authors have investigated the impedance variation of electric field antenna onboard scientific satellites in the photoelectron environment in space. From the preliminary simulation results, the large change of reactance of the antenna impedance below the characteristic frequency corresponding to the local plasma frequency determined by the photoelectron density could be confirmed
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Transient (computer programming)
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Abstract Plasma diagnostic instruments are carried into space by satellites to measure in situ the properties of space plasmas. However, due to spacecraft charging, satellites perturb the surrounding plasma, that reacts by enveloping the platform and its instruments with a short scale, strongly inhomogeneous plasma region called plasma sheath. Such plasma sheath perturbs particles and electric field measurements performed onboard the satellite. Mutual Impedance (MI) experiments are a type of in situ diagnostic technique used in several space missions for the identification of the plasma density and the electron temperature. The technique is based on the electric coupling between emitting and receiving electric sensors embedded in the plasma to diagnose. Such sensors are surrounded by the plasma sheath, which is expected to affect the plasma response to MI emissions. In this context, we quantify for the first time the impact of the plasma sheath on the diagnostic performance of MI experiments. For this purpose, we use a full kinetic Vlasov‐Poisson model to simulate numerically MI experiments in an inhomogeneous medium. For the first time, we explain the locality of MI measurements. We find that MI plasma density diagnostic are not affected by the plasma sheath ( dn / n < 10%). The experiment retrieves the density of the plasma unperturbed by the satellite's presence. The electron temperature diagnostic, instead, presents significant perturbations if the plasma sheath is ignored. To mitigate such electron temperature errors, the plasma sheath needs to be included in the analysis of MI measurements.
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Debye sheath
Astrophysical plasma
Electron temperature
Plasma parameter
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Electrostatic charging of satellites in space is a function of the spacecraft materials and various sources of charged particles. This paper explains how Langmuir probes as part of Plasma Wave Complex PWC aboard the Russian segment of the International Space Station, will monitor the surface charging of the station.
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Spacecraft charging
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Langmuir Probe
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space technology
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This paper is devoted towards the study and comparison of different techniques for measurement of electron density in low temperature plasma. To study the plasma profile it is necessary that one should know about its parameter. Electron density is one of the important plasma parameters of plasma profile. Other plasma parameters like plasma frequency, Debye length and dielectric parameter are also depended on the density of electron. For the plasma density measurement, there are various techniques and each technique has its own unique advantages and some disadvantages as well. Basic techniques for plasma density measurement are Langmuir and Resonance probe based measurement techniques, microwave interferometer and optical emission spectroscopy. This paper also covers basics about plasma parameters. In the first section plasma parameters and their importance is described in brief. Then, principle, analysis and experimental setup for all basic four techniques are included in next section. The last section is devoted towards the comparison of these unique techniques.
Langmuir Probe
Electron temperature
Plasma parameter
Debye
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Data from the Magnetospheric Multiscale (MMS) mission, in particular, the spacecraft potential measured with and without the ion beams of the active spacecraft potential control (ASPOC) instruments, plasma electron moments, and the electric field, have been employed for an improved determination of plasma density based on spacecraft potential. The known technique to derive plasma density from spacecraft potential sees the spacecraft behaving as a plasma probe which adopts a potential at which the ambient plasma current and one of photoelectrons produced at the surface and leaving into space are in equilibrium. Thus, the potential is a function of the plasma current, and plasma density can be determined using measurements or assumptions on plasma temperature. This method is especially useful during periods when the plasma instruments are not in operation or when spacecraft potential data have significantly higher time resolution than particle detectors. However, the applicable current-voltage characteristic of the spacecraft has to be known with high accuracy, particularly when the potential is actively controlled and shows only minor residual variations. This paper demonstrates recent refinements of the density determination coming from: 1) the reduction of artifacts in the potential data due to the geometry of the spinning spacecraft and due to effects of the ambient electric field on the potential measurements and 2) a calibration of the plasma current to the spacecraft surfaces which is only possible by comparison with the variable currents from the ion beams of ASPOC. The results are discussed, and plasma densities determined by this method are shown in comparison with measurements by the Fast Plasma Instrument (FPI) for some intervals of the MMS mission.
Spacecraft charging
Astrophysical plasma
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The differential charging of a nonconducting spacecraft is modeled numerically by following charged‐particle trajectories in a self‐consistent space‐charge‐less sheath. In the presence of a plasma flow but independent of any photoelectric or secondary emission a potential difference between the front and wake surfaces of the spacecraft is generated, resulting in an asymmetric sheath and in the creation of a potential barrier for electrons. The potential difference can amount to volts in the ionosphere and kilovolts in the solar wind. As in the more familiar case of photoelectric charging, the asymmetric sheath and potential barrier produced by the plasma flow can lead to erroneous interpretations of experiments measuring space electric fields and low‐energy particle spectra.
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Debye sheath
Photoelectric effect
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Langmuir electric probes and optical emission spectroscopy diagnostics were developed for applications in high density plasmas. These diagnostics were employed in two plasma sources: an electron cyclotron resonance (ECR) plasma and an RF driven inductively coupled plasma (ICP) plasma. Langmuir probes were tested using a number of probing dimensions, probe tip materials, circuits for probe bias and filters. Then, the results were compared with the optical spectroscopy measurements. With these diagnostics, analyses of various plasma processes were performed in both reactors. For example, it has been shown that species like NH radicals generated in gas phase can have critical impact on films deposited by ECR plasmas. In the ICP source, plasmas in atomic and molecular gases were shown to have different spatial distributions, likely due to nonlocal electron heating. The low‐to‐high density transitions in the ICP plasma were also studied. The role of metastables is shown to be significant in Ar plasmas, in contrast to plasmas with additions of molecular gases.
Langmuir Probe
Electron temperature
Electron cyclotron resonance
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Spacecraft charging
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