scholarly journals Cooling of Electrons in a Weakly Outgassing Comet

2020 ◽  
Author(s):  
Peter Stephenson ◽  
Marina Galand ◽  
Jan Deca ◽  
Pierre Henri ◽  
Gianluca Carnielli
Keyword(s):  
Solar Wind ◽  
Extreme Ultraviolet ◽  
Pure Water ◽  
Particle Model ◽  
Particle In Cell ◽  
Electron Sources ◽  
Cometary Plasma ◽  
Impedance Probe ◽  
Cold Electrons ◽  
The Impact

<p>The plasma instruments, Mutual Impedance Probe (MIP) and Langmuir Probe (LAP), part of the Rosetta Plasma Consortium (RPC), onboard the Rosetta mission to comet 67P revealed a population of cold electrons (<1eV) (Engelhardt et al., 2018; Wattieaux et al, 2020; Gilet et al., 2020). This population is primarily generated by cooling warm (~10eV) newly-born cometary electrons through collisions with the neutral coma. What is surprising is that the cold electrons were detected throughout the escort phase, even at very low outgassing rates (Q<1e26 s<sup>-1</sup>) at large heliocentric distances (>3 AU), when the coma was not thought to be dense enough to cool the electron population significantly.</p> <p> Using a collisional test particle model, we examine the behaviour of electrons in the coma of a weakly outgassing comet and the formation of a cold population through electron-neutral collisions. The model incorporates three electron sources: the solar wind, photo-electrons produced through ionisation of the cometary neutrals by extreme ultraviolet solar radiation, and secondary electrons produced through electron-impact ionisation.</p> <p>The model includes different electron-water collision processes, including elastic, excitation, and ionisation collisions.</p> <p> The electron trajectories are shaped by electric and magnetic fields, which are taken from a 3D collisionless fully-kinetic Particle-in-Cell (PIC) model of the solar wind and cometary plasma  (Deca 2017, 2019). We use a spherically symmetric coma of pure water, which gives a r<sup>-2</sup> profile in the neutral density. Throughout their lifetime, electrons undergo stochastic collisions with neutral molecules, which can degrade the electrons in energy or scatter them.</p> <p>We first validate our model with comparison to results from PIC simulations. We then demonstrate the trapping of electrons in the coma by an ambipolar electric field and the impact of this trapping on the production of cold electrons.</p>

Electron cooling at a weakly outgassing comet

2021 ◽  
Author(s):  
Peter Stephenson ◽  
Marina Galand ◽  
Jan Deca ◽  
Pierre Henri ◽  
Gianluca Carnielli
Keyword(s):  
Pure Water ◽  
Particle Model ◽  
Cold Electron ◽  
Subsequent Formation ◽  
Electron Population ◽  
Particle In Cell ◽  
Neutral Gas ◽  
Test Particles ◽  
Impedance Probe ◽  
Cold Electrons

<p>The Rosetta spacecraft arrived at comet 67P in August 2014 and then escorted it for 2 years along its orbit. Throughout this escort phase, two plasma instruments (Mutual Impedance Probe, MIP; and Langmuir Probe, LAP) measured a population of cold electrons (< 1 eV) within the coma of 67P (Engelhardt et al., 2018; Wattieaux et al, 2020; Gilet et al., 2020). These cold electrons are understood to be formed by cooling warm electrons through collisions with the neutral gas. The warm electrons are primarily newly-born and produced at roughly 10eV within the coma through ionisation. While it was no surprise that cold electrons would form near perihelion given the high density of the neutral coma, the persistence of the cold electrons up to a heliocentric distance of 3.8 au was highly unexpected. With the low outgassing rates observed at such large heliocentric distances (Q < 10<sup>26</sup> s<sup>-1</sup>), there should not be enough neutral molecules to cool the warm electrons efficiently before they ballistically escape the coma.</p><p>We use a collisional test particle model to examine the formation of the cold electron population at a weakly outgassing comet. The electrons are subject to stochastic collisions with the neutral coma which can either scatter or cool the electrons. Multiple electron neutral collision processes are included such that the electrons can undergo elastic scattering as well as collisions inducing excitation and ionisation of the neutral species. The inputted electric and magnetic fields, which act on the test particles, are taken from a 3D fully-kinetic, collisionless Particle-in-Cell (PiC) model of the solar wind and cometary ionosphere (Deca et al., 2017; 2019), with the same neutral coma as used in our model. We use a pure water coma with spherical symmetry and a 1/r<sup>2</sup> dependence in the neutral number density to drive the production of cometary electrons and the electron-neutral collisions.</p><p>We first demonstrate the trapping of electrons in a potential well around the comet nucleus, formed by an ambipolar field. We show how this electron-trapping process can lead to more efficient cooling of electrons and the subsequent formation of a cold electron population, even at low outgassing rates.</p>

Microinstabilities and plasma waves at Near-Sun Solar Wind collisionless Shocks: Predictions for PSP and SO

2021 ◽  
Author(s):  
Zhongwei Yang ◽  
Shuichi Matsukiyo ◽  
Huasheng Xie ◽  
Fan Guo ◽  
Mingzhe Liu ◽  
...  
Keyword(s):  
Solar Wind ◽  
Shock Front ◽  
Leading Edge ◽  
Relativistic Electrons ◽  
Interplanetary Shocks ◽  
Particle In Cell ◽  
Drift Instability ◽  
Shock Simulation ◽  
Mass Ejection ◽  
The Impact

<p><span>Microinstabilities and waves excited at perpendicular interplanetary shocks in the near-Sun solar wind are investigated by full particle-in-cell simulations. By analyzing the dispersion relation of fluctuating field components directly issued from the shock simulation, we obtain key findings concerning wave excitations at the shock front: (1) at the leading edge of the foot, two types of electrostatic (ES) waves are observed. The relative drift of the reflected ions versus the electrons triggers an electron cyclotron drift instability (ECDI) that excites the first ES wave. Because the bulk velocity of gyro-reflected ions shifts to the direction of the shock front, the resulting ES wave propagates obliquely to the shock normal. Immediately, a fraction of incident electrons are accelerated by this ES wave and a ring-like velocity distribution is generated. They can couple with the hot Maxwellian core and excite the second ES wave around the upper hybrid frequency. (2) From the middle of the foot all the way to the ramp, electrons can couple with both incident and reflected ions. ES waves excited by ECDI in different directions propagate across each other. Electromagnetic (EM) waves (X mode) emitted toward upstream are observed in both regions. They are probably induced by a small fraction of relativistic electrons. The impact of shock front rippling, Mach numbers, and dimensions on the ES wave excitation also will be discussed. Results shed new insight on the mechanism for the occurrence of ES wave excitations and possible EM wave emissions at young coronal mass ejection–driven shocks in the near-Sun solar wind.</span></p>

scholarly journals Unusually high magnetic fields in the coma of 67P/Churyumov-Gerasimenko during its high-activity phase

2019 ◽  
Vol 630 ◽  
pp. A38 ◽  
Author(s):  
C. Goetz ◽  
B. T. Tsurutani ◽  
P. Henri ◽  
M. Volwerk ◽  
E. Behar ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Unusual Behavior ◽  
Cometary Plasma ◽  
Unusual Event ◽  
Interplanetary Coronal Mass Ejection ◽  
Magnetic Field Magnitude ◽  
Solar Wind Origin ◽  
The Impact ◽  
The Magnetic Field

Aims. On July 3, 2015, an unprecedented increase in the magnetic field magnitude was measured by the Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko (67P). This increase was accompanied by large variations in magnetic field and ion and electron density and energy. To our knowledge, this unusual event marks the highest magnetic field ever measured in the plasma environment of a comet. Our goal here is to examine possible physical causes for this event, and to explain this reaction of the cometary plasma and magnetic field and its trigger. Methods. We used observations from the entire Rosetta Plasma Consortium as well as energetic particle measurements from the Standard Radiation Monitor on board Rosetta to characterize the event. To provide context for the solar wind at the comet, observations at Earth were compared with simulations of the solar wind. Results. We find that the unusual behavior of the plasma around 67P is of solar wind origin and is caused by the impact of an interplanetary coronal mass ejection, combined with a corotating interaction region. This causes the magnetic field to pile up and increase by a factor of six to about 300 nT compared to normal values of the enhanced magnetic field at a comet. This increase is only partially accompanied by an increase in plasma density and energy, indicating that the magnetic field is connected to different regions of the coma.

scholarly journals Forming a cold electron population at a weakly outgassing comet 

2021 ◽  
Author(s):  
Peter Stephenson ◽  
Marina Galand ◽  
Jan Deca ◽  
Pierre Henri ◽  
Gianluca Carnielli
Keyword(s):  
Test Particle ◽  
Extreme Ultraviolet ◽  
Pure Water ◽  
Particle Model ◽  
Cold Electron ◽  
Electron Population ◽  
Neutral Gas ◽  
Rosetta Mission ◽  
Radial Outflow ◽  
Comet 67P

<p>The Rosetta Mission rendezvoused with comet 67P/Churyumov-Gerasimenko in August 2014 and escorted it for two years along its orbit. The Rosetta Plasma Consortium (RPC) was a suite of instruments, which observed the plasma environment at the spacecraft throughout the escort phase. The Mutual Impedance Probe (RPC/MIP; Wattieaux et al, 2020; Gilet et al., 2020) and Langmuir Probe (RPC/LAP; Engelhardt et al., 2018), both part of RPC, measured the presence of a cold electron population within the coma.</p> <p>Newly born electrons, generated by ionisation of the neutral gas, form a warm population within the coma at ~10eV. Ionisation is either through absorption of extreme ultraviolet photons or through collisions of energetic electrons with the neutral molecules. The cold electron population is formed by cooling the newly born, warm electrons via electron-neutral collisions. Assuming the radial outflow of electrons, the cold population was only expected at comet 67P close to perihelion, where outgassing rate from the nucleus was at its highest (Q > 10<sup>28</sup> s<sup>-1</sup>). However, cold electrons were observed until the end of the Rosetta mission at 3.8au when the outgassing was weak (Q<10<sup>26</sup> s<sup>-1</sup>). Under the radial outflow assumption, there should not have been sufficient neutral gas to efficiently degrade the electron energies.</p> <p>We have developed the first 3D collision model of electrons at a comet. Self-consistently calculated electric and magnetic fields from a collisionless and fully-kinetic Particle-in-Cell model (Deca et al., 2017; 2019) are used as a stationary input for the test particle simulations. We model the neutral coma as a spherically symmetric cloud of pure water, which follows 1/r<sup>2</sup> in cometocentric distance. Electron-neutral collisions are treated as a stochastic process using cross sections from Itikawa and Mason (2005). The model incorporates elastic scattering of electrons and a variety of inelastic collisions, including excitation and ionization of the water molecules.</p> <p>We show that the radial outflow of electrons from the coma is insufficient to generate a cold electron population under weak outgassing conditions. Using our original test particle model, we demonstrate the trapping of electrons in the inner coma by an ambipolar electric field and how this increases the efficiency of the electron cooling.  We also show that, at low outgassing rates, electron-neutral collisions significantly cool electrons within the coma and can lead to the formation of a cold population.</p> <p> </p>

The influence of crustal magnetic fields on the Martian bow shock : a statistical analysis of Mars Volatile EvolutioN and Mars Express observations

2020 ◽  
Author(s):  
Philippe Garnier ◽  
Christian Jacquey ◽  
Christian Mazelle ◽  
Xiaohua Fang ◽  
Jacob Gruesbeck ◽  
...  
Keyword(s):  
Solar Wind ◽  
Magnetic Fields ◽  
Extreme Ultraviolet ◽  
Dynamic Pressure ◽  
Bow Shock ◽  
Machine Learning Techniques ◽  
Mars Atmosphere ◽  
Mars Express ◽  
Shock Location ◽  
The Impact

<p>The Martian interaction with the solar wind is unique due to the influence of remanent crustal magnetic fields. The recent studies by the Mars Express and Mars Atmosphere and Volatile Evolution missions underline the strong and complex influence of the crustal magnetic fields on the Martian environment and its interaction with the solar wind. Among them is the influence on the dynamic plasma boundaries that shape this interaction and on the bow shock in particular.</p> <p>Compared to other drivers of the shock location (e.g. solar dynamic pressure, extreme ultraviolet fluxes), the influence of crustal magnetic fields are less understood, with essentially differences observed between the southern and northern hemispheres attributed to the crustal fields. In this presentation we analyze in detail the influence of the crustal fields on the Martian shock location by combining for the first time datasets from two different spacecraft (MAVEN/MEX). An application of machine learning techniques will also be used to increase the list of MAVEN shocks published to date. We show in particular the importance for analyzing biases due to multiple parameters of influence through a partial correlation approach. We also compare the impact of crustal fields with the other parameters of influence, and show that the main drivers of the shock location are by order of importance extreme ultraviolet fluxes and magnetosonic Mach number, crustal fields and then solar wind dynamic pressure.</p>

Fractality of Simulated Fracture

2009 ◽  
Vol 409 ◽  
pp. 154-160 ◽  
Author(s):  
Petr Frantík ◽  
Zbyněk Keršner ◽  
Václav Veselý ◽  
Ladislav Řoutil
Keyword(s):  
Numerical Model ◽  
Elastic Plate ◽  
Model Simulation ◽  
Element Model ◽  
The Other ◽  
Particle Model ◽  
Discrete Element Model ◽  
Fractal Nature ◽  
Discrete Elements ◽  
The Impact

The paper is focussed on numerical simulations of the fracture of a quasi-brittle specimen due to its impact onto a fixed rigid elastic plate. The failure of the specimen after the impact is modelled in two ways based on the physical discretization of continuum: via physical discrete elements and pseudo-particles. Advantages and drawbacks of both used methods are discussed. The size distribution of the fragments of the broken specimen resulting from physical discrete element model simulation follows a power law, which indicates the ability of the numerical model to identify the fractal nature of the fracture. The pseudo-particle model, on the other side, can successfully predict the kinematics of the fragments of the specimen under impact failure.

The Impact of Solar Winds on Navigation Aids

1999 ◽  
Vol 52 (1) ◽  
pp. 42-46 ◽  
Author(s):  
W. H. Sandford
Keyword(s):  
Solar Wind ◽  
Media Coverage ◽  
Scientific Community ◽  
The United States ◽  
Public Attention ◽  
Remote Imaging ◽  
Solar Winds ◽  
New Information ◽  
Recent Developments ◽  
The Impact

Recent developments in remote imaging equipment carried on satellites have given the scientific community a vast amount of new information about the Sun and its atmosphere. Media coverage of the remarkable discoveries accompanied by impressive images of the Sun's atmosphere, and linkage to the loss of a television satellite over the United States, have focused public attention on the existence and effects of the Solar Wind. This paper sets out to illustrate the impact of the Solar Wind on radio aids to navigation, and to look at the possible effects on present and proposed systems.

scholarly journals Experimental Study on Limestone Cohesive Particle Model and Crushing Simulation

2018 ◽  
Vol 2018 ◽  
pp. 1-12
Author(s):  
Huaiying Fang ◽  
Dawei Xing ◽  
Jianhong Yang ◽  
Fulin Liu ◽  
Junlong Chen ◽  
...  
Keyword(s):  
Particle Size ◽  
Simulation Model ◽  
Impact Velocity ◽  
Distribution Curve ◽  
Particle Model ◽  
Particle Sizes ◽  
Particle Crushing ◽  
Discrete Element Method Simulation ◽  
Impact Crushing ◽  
The Impact

This study investigates the effect of impact velocity and particle size on crushing characteristics. We use a discrete-element method simulation and construct cohesive limestone particles with internal microinterfaces and cracks for impact crushing experimentation. The simulation model follows the same process as the impact crushing experiment. Results show that, after crushing at impact velocities of 30 and 40 m/s, the simulated particle-size distribution curve matches experimental results as closely as 95%. For different particle sizes, results are more than 90% in agreement. These results indicate the feasibility of the cohesive-particle crushing simulation model. When the particle size is 15 mm, an approximate linear relationship exists on impact velocity and crushing ratio. For a constant impact velocity, the particle size of 18 mm results in the maximum crushing ratio.

scholarly journals Ion-driven Instabilities in the Inner Heliosphere. I. Statistical Trends

2021 ◽  
Vol 923 (1) ◽  
pp. 116
Author(s):  
Mihailo M. Martinović ◽  
Kristopher G. Klein ◽  
Tereza Ďurovcová ◽  
Benjamin L. Alterman
Keyword(s):  
Solar Wind ◽  
Particle Interaction ◽  
Radial Distance ◽  
Solar Wind Plasma ◽  
Distribution Functions ◽  
Nyquist Criterion ◽  
Velocity Distribution Functions ◽  
Instability Growth ◽  
Statistical Trends ◽  
The Impact

Abstract Instabilities described by linear theory characterize an important form of wave–particle interaction in the solar wind. We diagnose unstable behavior of solar wind plasma between 0.3 and 1 au via the Nyquist criterion, applying it to fits of ∼1.5M proton and α particle Velocity Distribution Functions (VDFs) observed by Helios I and II. The variation of the fraction of unstable intervals with radial distance from the Sun is linear, signaling a gradual decline in the activity of unstable modes. When calculated as functions of the solar wind velocity and Coulomb number, we obtain more extreme, exponential trends in the regions where collisions appear to have a notable influence on the VDF. Instability growth rates demonstrate similar behavior, and significantly decrease with Coulomb number. We find that for a nonnegligible fraction of observations, the proton beam or secondary component might not be detected, due to instrument resolution limitations, and demonstrate that the impact of this issue does not affect the main conclusions of this work.

scholarly journals A Short Note about the Impact Action of a Water Jet Stabilized by a Coaxial Air Stream in the Air and Underwater

Materials ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5015
Author(s):  
Josef Poláček ◽  
Irena Marie Hlaváčová ◽  
Martin Tyč
Keyword(s):  
Near Field ◽  
Pure Water ◽  
Air Flow ◽  
Relevant Literature ◽  
Short Note ◽  
Original Method ◽  
Water Jet ◽  
Impact Action ◽  
Dual Action ◽  
The Impact

A new original method, applying a coaxial protective airflow, was tested aiming to improve the pure water jet efficiency in surface layer removal or medium hard materials cutting or blasting. The dual action of the air flow is expected: the air co-flowing the water jet with approximately the same velocity should prevent the central jet from breaking up into tiny droplets in the near field, and simultaneously, it should support jet decomposition into big parts with enough destructive potential in the far-field. A brief survey of the relevant literature dealing with the water jet instability is presented, introducing four recognized breakup regimes. An original cutting head designed to generate a waterjet surrounded by protective coaxial air flow is introduced. The submitted device is supposed to operate within the first wind-induced regime. Two types of experiments, consisting of blasting limestone bricks placed either in the air or underwater, were realized. The depths of kerfs produced with different water pressures and air overpressures were evaluated. While no substantial positive effect was recognized in the air performance, the submerged blasting of the same material under similar conditions appeared to be promising.

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