Observations of low energy ions around the diamagnetic cavity at comet 67P

2020 ◽  
Author(s):  
Gabriella Stenberg Wieser ◽  
Martin Wieser ◽  
Sofia Bergman ◽  
Elias Odelstad ◽  
Fredrik Johansson ◽  
...  
Keyword(s):  
Ion Flux ◽  
Low Energy ◽  
Electron Velocity ◽  
Ion Dynamics ◽  
Ion Temperature ◽  
Electron Velocity Distribution ◽  
Spacecraft Potential ◽  
Sudden Decrease ◽  
Low Energy Ions ◽  
Comet 67P

<p>We investigate the variations in low energy cometary ions around comet 67P. Detailed measurements of these ions were made possible by implementing a new instrumental mode of the ion mass spectrometer on the Rosetta spacecraft. The nominal time resolution was increased from 192 s to 4 s at the expense of the energy range and the field-of-view.</p><p>In this study we focus on ion observations made outside of, but in the vicinity of, the diamagnetic cavity. The ion dynamics here is clearly linked to variations of the magnetic field strength and properties of the electron velocity distribution, manifested by the spacecraft potential. Preliminary results show that the ion flux correlates with the changes of the spacecraft potential. The maximum ion flux is, however, observed about 20 seconds after a sudden decrease of the potential (corresponding to an increase in electron density if electron temperature is constant). We also find evidence of small ion temperature increases both when the spacecraft potential changes fast and at the time of maximum ion flux.</p>

scholarly journals Flow directions of low-energy ions in and around the diamagnetic cavity of comet 67P

2021 ◽  
Author(s):  
Sofia Bergman ◽  
Gabriella Stenberg Wieser ◽  
Martin Wieser ◽  
Hans Nilsson ◽  
Erik Vigren ◽  
...  
Keyword(s):  
Flow Direction ◽  
Low Energy ◽  
Expansion Velocity ◽  
Directional Information ◽  
Particle In Cell ◽  
Spacecraft Potential ◽  
Cell Simulation ◽  
Flow Directions ◽  
Low Energy Ions ◽  
Comet 67P

Abstract The flow direction of low-energy ions around comet 67P/Churyumov-Gerasimenko has previously been difficult to constrain due to the influence of the spacecraft potential. The Ion Composition Analyzer of the Rosetta Plasma Consortium (RPC-ICA) on Rosetta measured the distribution function of positive ions with energies down to just a few eV/q throughout the escort phase of the mission. Unfortunately, the substantial negative spacecraft potential distorted the directional information of the low-energy data. In this work, we present the flow directions of low-energy ions around comet 67P, corrected for the spacecraft potential using Particle-In-Cell simulation results. We focus on the region in and around the diamagnetic cavity, where low-energy ions are especially important for the dynamics. We separate between slightly accelerated “burst” features and a more constant “band” of low-energy ions visible in the data. The “bursts” are flowing radially outwards from the nucleus with an anti-sunward component while the “band” is predominantly streaming back towards the comet. This provides evidence of counter-streaming ions, which has implications for the overall expansion velocity of the ions. The backstreaming ions are present also at times when the diamagnetic cavity was not detected, indicating that the process accelerating the ions back towards the comet is not connected to the cavity boundary.

scholarly journals Cluster PEACE observations of electrons of spacecraft origin

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1721-1730 ◽  
Author(s):  
S. Szita ◽  
A. N. Fazakerley ◽  
P. J. Carter ◽  
A. M. James ◽  
P. Trávnícek ◽  
...  
Keyword(s):  
High Energy ◽  
Plasma Electron ◽  
Electron Velocity ◽  
Lunar Eclipse ◽  
Arrival Direction ◽  
Electron Velocity Distribution ◽  
Potential Control ◽  
Spacecraft Potential ◽  
Solar Uv ◽  
Gradient Change

Abstract. The two PEACE (Plasma Electron And Current Experiment) sensors on board each Cluster spacecraft sample the electron velocity distribution across the full 4<pi> solid angle and the energy range 0.7 eV to 26 keV with a time resolution of 4 s. We present high energy and angular resolution 3D observations of electrons of spacecraft origin in the various environments encountered by the Cluster constellation, including a lunar eclipse interval where the spacecraft potential was reduced but remained positive, and periods of ASPOC (Active Spacecraft POtential Control) operation which reduced the spacecraft potential. We demonstrate how the spacecraft potential may be found from a gradient change in the PEACE low energy spectrum, and show how the observed spacecraft electrons are confined by the spacecraft potential. We identify an intense component of the spacecraft electrons with energies equivalent to the spacecraft potential, the arrival direction of which is seen to change when ASPOC is switched on. Another spacecraft electron component, observed in the sunward direction, is reduced in the eclipse but unaffected by ASPOC, and we believe this component is produced in the analyser by solar UV. We find that PEACE anodes with a look direction along the spacecraft surfaces are more susceptible to spacecraft electron contamination than those which look perpendicular to the surface, which justifies the decision to mount PEACE with its field-of-view radially outward rather than tangentially.Key words. Magnetosheric physics (general or miscellaneous) Space plasma physics (spacecraft sheaths, wakes, charging)

Ion bulk speeds and temperatures in the diamagnetic cavity of comet 67P

2021 ◽  
Author(s):  
Sofia Bergman ◽  
Gabriella Stenberg Wieser ◽  
Martin Wieser ◽  
Fredrik Leffe Johansson ◽  
Erik Vigren ◽  
...  
Keyword(s):  
Energy Spectrum ◽  
Low Energy ◽  
High Time Resolution ◽  
Langmuir Probes ◽  
Ion Distribution ◽  
Strongly Coupled ◽  
Neutral Particles ◽  
Spacecraft Potential ◽  
Impedance Probe ◽  
Comet 67P

&lt;p&gt;The formation and maintenance of the diamagnetic cavity around comets is a debated subject. For active comets such as 1P/Halley, the ion-neutral drag force is suggested to balance the outside magnetic pressure at the cavity boundary, but measurements made by Rosetta at the intermediately active comet 67P/Churyumov-Gerasimenko indicate that the situation might be different at less active comets. Measurements from the Langmuir probes and the Mutual Impedance Probe on board Rosetta, as well as modelling efforts, show ion velocities significantly above the velocity of the neutral particles, indicating that the ions are not as strongly coupled to the neutrals at comet 67P.&lt;/p&gt;&lt;p&gt;In this study we use low-energy high time resolution data from the Ion Composition Analyzer (ICA) on Rosetta to determine the bulk speeds and temperatures of the ions inside the diamagnetic cavity of comet 67P. The interpretation of the low-energy data is not straight forward due to the complicated influence of the spacecraft potential, but a newly developed method utilizing simulations with the Spacecraft Plasma Interaction Software (SPIS) software makes it possible to extract the original properties of the ion distribution. We use SPIS to model the influence of the spacecraft potential on the energy spectrum of the ions, and fit the energy spectrum sampled by ICA to the simulation results. This gives information about both the bulk speed and temperature of the ions.&lt;/p&gt;&lt;p&gt;The results show bulk speeds of 5-10 km/s, significantly above the speed of the neutral particles, and temperatures of 0.7-1.6 eV. The major part of this temperature is attributed to ions being born at different locations in the coma, and could hence be considered a dispersion rather than a temperature in the classical sense. The high bulk speeds support previous results, indicating that the collisional coupling between ions and neutrals is weak inside the diamagnetic cavity.&lt;/p&gt;

The Spacecraft Potential’s Influence on the FOV of Rosetta-ICA at Low Ion Energies

2020 ◽  
Author(s):  
Sofia Bergman ◽  
Gabriella Stenberg Wieser ◽  
Martin Wieser ◽  
Fredrik Johansson ◽  
Anders Eriksson
Keyword(s):  
Debye Length ◽  
Low Energy ◽  
In Situ Techniques ◽  
Positive Ions ◽  
Spacecraft Potential ◽  
Energy Part ◽  
Ion Energies ◽  
Low Energies ◽  
Composition Analyzer ◽  
Low Energy Ions

&lt;p&gt;&lt;span&gt;Low-energy ions play important roles in many processes in the environments around various bodies in the solar system. At comets, they are, for example, important for the understanding of the interaction of the cometary particles with the solar wind, including the formation of the diamagnetic cavity. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Unfortunately, spacecraft charging makes low-energy ions difficult to measure using in-situ techniques. The charged spacecraft surface will attract or repel the ions prior to detection, affecting both their trajectories and energy. The affected trajectories will change the effective FOV of the instrument. A negatively charged spacecraft will focus incoming positive ions, enlarging and distorting the FOV.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;We model the low-energy FOV distortion of the Ion Composition Analyzer (ICA) on board Rosetta. ICA is an ion spectrometer measuring positive ions with an energy range of a few eV to 40 keV. Rosetta was commonly charged to a negative potential throughout the mission, and consequently the positive ions were accelerated towards the spacecraft before detection. This distorted the low-energy part of the data. We use the Spacecraft Plasma Interaction Software (SPIS) to simulate the environment around the spacecraft and backtrace particles from the instrument. We then compare the travel direction of the ions at detection and infinity, and draw conclusions about the resulting FOV distortion. We investigate the distortion for different spacecraft potentials and Debye lengths of the surrounding plasma. &lt;/span&gt;&lt;/p&gt;&lt;p&gt; &lt;span&gt;The results show that the effective FOV of ICA is severely distorted at low energies, but the distortion varies between different viewing directions of the instrument. It is furthermore sensitive to changes in the Debye length and we observe a small non-linearity in the relation between FOV distortion, ion energy and spacecraft potential. Generally, the FOV is not significantly affected when the energy of the ions is above twice the spacecraft potential. &lt;/span&gt;&lt;/p&gt;

scholarly journals Outflow of low-energy O<sup>+</sup> ion beams observed during periods without substorms

2015 ◽  
Vol 33 (3) ◽  
pp. 333-344 ◽  
Author(s):  
G. K. Parks ◽  
E. Lee ◽  
S. Y. Fu ◽  
M. Fillingim ◽  
I. Dandouras ◽  
...  
Keyword(s):  
Flow Rate ◽  
Heavy Ion ◽  
Auroral Oval ◽  
Ion Beams ◽  
Low Energy ◽  
Ion Composition ◽  
Spacecraft Potential ◽  
Imaging Camera ◽  
Cluster Ion ◽  
Low Energy Ions

Abstract. Numerous observations have shown that ions flow out of the ionosphere during substorms with more fluxes leaving as the substorm intensity increases (Wilson et al., 2004). In this article we show observations of low-energy (few tens of electron volts) ionospheric ions flowing out periods without substorms, determined using the Wideband Imaging Camera (WIC) and Auroral Electrojet (AE) indices. We use Cluster ion composition data and show the outflowing ions are field-aligned H+, He+ and O+ beams accelerated to energies of ~40–80 eV, after correcting for spacecraft potential. The estimated fluxes of the low-energy O+ ions measured at ~20 000 km altitude are >103–105 cm−2 s. Assuming the auroral oval is the source of the escaping ions, the measured fluxes correspond to a flow rate of ~1019–1021 ions s−1 leaving the ionosphere. However, periods without substorms can persist for hours suggesting the low-energy ions flowing out during these times could be a major source of the heavy ion population in the plasma sheet and lobe.

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