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.

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>

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

<p>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.</p><p>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.</p><p>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.</p>

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

<p><span>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. </span></p><p><span>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.</span></p><p><span>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. </span></p><p> <span>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. </span></p>

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.

Particle-In-Cell Simulation for Breakdown Phenomena in Vacuum

2020 ◽  
Vol 140 (6) ◽  
pp. 318-324
Author(s):  
Haruki Ejiri ◽  
Takashi Fujii ◽  
Akiko Kumada ◽  
Kunihiko Hidaka
Keyword(s):  
Particle In Cell ◽  
Cell Simulation

Ion-Assisted Surface Processing of Electronic Materials

MRS Bulletin ◽  
1992 ◽  
Vol 17 (6) ◽  
pp. 52-57 ◽  
Author(s):  
S.T. Picraux ◽  
E. Chason ◽  
T.M. Mayer
Keyword(s):  
Plasma Etching ◽  
Electronic Materials ◽  
Low Energy ◽  
Surface Processing ◽  
Wave Guides ◽  
Side Walls ◽  
Wet Chemical ◽  
Low Energy Ions ◽  
Metal Layers ◽  
Defect Densities

Why are low-energy ions relevant to the surface processing of electronic materials? The answer lies in the overriding trend of miniaturization in microelectronics. The achievement of these feats in ultrasmall architecture has required surface processing capabilities that allow layer addition and removal with incredible precision. The resulting benefits of greater capacity and speed at a plummeting cost per function are near legendary.The ability of low-energy ions to enhance the precision of surface etching, cleaning, and deposition/growth processes (Figure 1) provides one basis for the interest in ion-assisted processes. Low-energy ions are used, for example, to enhance the sharpness of side walls in plasma etching and to improve step coverage by metal layers in sputter deposition. Emerging optoelectronic applications such as forming ridges for wave-guides and ultrasmooth vertical surfaces for lasers further extend piesent requirements, and low-energy ions again provide one tool to help in this area of ultraprecise materials control. Trends associated with the decreased feature size include the movement from wet chemical processing to dry processing, the continuing need for reductions in defect densities, and the drive toward reduced temperatures and times in process steps.How do the above trends focus interest on studies of low-energy ion-assisted processes? In current applications, these trends are driving the need for increased atomic-level understanding of the ion-enhancement mechanisms, for example, in reactive ion etching to minimize defect production and enhance surface chemical reactions.

scholarly journals A generalized weight-based particle-in-cell simulation scheme

2011 ◽  
Vol 182 (3) ◽  
pp. 564-569 ◽  
Author(s):  
W.W. Lee ◽  
T.G. Jenkins ◽  
S. Ethier
Keyword(s):  
Particle In Cell ◽  
Cell Simulation ◽  
Simulation Scheme
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