ViDA: a Vlasov–DArwin solver for plasma physics at electron scales

We present a Vlasov–DArwin numerical code (ViDA) specifically designed to address plasma physics problems, where small-scale high accuracy is requested even during the nonlinear regime to guarantee a clean description of the plasma dynamics at fine spatial scales. The algorithm provides a low-noise description of proton and electron kinetic dynamics, by splitting in time the multi-advection Vlasov equation in phase space. Maxwell equations for the electric and magnetic fields are reorganized according to the Darwin approximation to remove light waves. Several numerical tests show that ViDA successfully reproduces the propagation of linear and nonlinear waves and captures the physics of magnetic reconnection. We also discuss preliminary tests of the parallelization algorithm efficiency, performed at CINECA on the Marconi-KNL cluster. ViDA will allow the running of Eulerian simulations of a non-relativistic fully kinetic collisionless plasma and it is expected to provide relevant insights into important problems of plasma astrophysics such as, for instance, the development of the turbulent cascade at electron scales and the structure and dynamics of electron-scale magnetic reconnection, such as the electron diffusion region.

Download Full-text

Ionospheric ions in the magnetosphere: Important at large and small scales

10.5194/egusphere-egu2020-3653 ◽

2020 ◽

Author(s):

Mats André ◽

Sergio Toledo-Redondo ◽

Andrew W Yau

Keyword(s):

Electric Field ◽

Magnetic Reconnection ◽

Energy Transport ◽

Small Scale ◽

Diffusion Region ◽

Positive Ions ◽

Small Scales ◽

Outflow Rate ◽

Long Time ◽

Cold Ions

Cold (eV) ions of ionospheric origin dominate the number density of most of the volume of the magnetosphere during most of the time. Supersonic flows of cold positive ions are common and can cause a negatively charged wake behind a positively charged spacecraft. The associated induced electric field can be observed and can be used to study the cold ions. We present observations from the Cluster and MMS spacecraft showing how a charged satellite, and also individual charged wire booms of &#160;an electric field instrument, can be used to investigate cold ion populations. Ionospheric ions affect large scales, including the Alfv&#233;n velocity and &#160;thus energy transport with waves and the magnetic reconnection rate. These ions also affect small-scale kinetic plasma physics, including the Hall physics and wave instabilities associated with magnetic reconnection. Concerning large scales, we summarize observations from several spacecraft and show that a typical total outflow rate of ionospheric ions is 1026 ions/s and that many of these ions stay cold also after a long time in the magnetosphere.&#160; Concerning small scales, we show examples of how cold ions modify the Hall physics of thin current sheets, including magnetic reconnection separatrices. On small kinetic scales the cold ions introduce a new length-scale, a gyro radius between the gyro radii of hot (keV) ions and electrons. The Hall currents carried by electrons can be partially cancelled by the cold ions when electrons and the magnetized cold ions ExB drift together. Also, close to a reconnection X-line an additional diffusion region can be formed (regions associated with hot and cold ions, and with electrons, total of three).

Download Full-text

Collisionless magnetic reconnection dynamics with electron inertia and parallel electron compressibility

Journal of Plasma Physics ◽

10.1017/s0022377806006313 ◽

2007 ◽

Vol 73 (6) ◽

pp. 857-868 ◽

Cited By ~ 2

Author(s):

BHIMSEN K. SHIVAMOGGI

Keyword(s):

Magnetic Reconnection ◽

Neutral Line ◽

Collisionless Plasma ◽

Sufficient Conditions ◽

Steady States ◽

Plasma Dynamics ◽

Electron Inertia ◽

Current Confinement ◽

Field Lines ◽

Lyapunov Sense

AbstractCollisionless magnetic reconnection dynamics is considered by including the effects of electron inertia as well as parallel electron compressibility. A fluid treatment is adopted for both electrons and ions. Collisionless plasma dynamics properties near a two-dimensional X-type magnetic neutral line in the steady state are explored. The effects of electron inertia and parallel electron compressibility on the hyperbolicity (or lack thereof) of the magnetic field lines in the neutral layer are discussed. A unified linear tearing-mode formulation incorporating both electron inertia and parallel electron compressibility is given. The parallel-electron-compressibility branch is shown to couple in general to the electron-inertia branch in the presence of resistivity. A sufficient condition for linear stability in the Lyapunov sense for steady states of this collisionless plasma system signifying current confinement is deduced. Bounds on the equilibrium current gradient are shown to constitute sufficient conditions for nonlinear stability in the Lyapunov sense for steady states via nonlinear bounds for a suitable perturbation norm.

Download Full-text

MMS observations of electron firehose fluctuations in the magnetic reconnection outflow

10.5194/egusphere-egu21-14401 ◽

2021 ◽

Author(s):

Giulia Cozzani ◽

Yuri Khotyaintsev ◽

Daniel Graham ◽

Mats André

Keyword(s):

Energy Conversion ◽

Electron Temperature ◽

Magnetic Reconnection ◽

Diffusion Region ◽

Temperature Anisotropy ◽

Plasma Dynamics ◽

Background Magnetic Field ◽

Outflow Region ◽

Reconnection Site

Plasma waves and instabilities driven by temperature anisotropies are known to play a significant role in plasma dynamics, scattering the particles and affecting particle heating and energy conversion between the electromagnetic fields and the particles. Among these instabilities, the electron firehose instability is driven by electron temperature anisotropy Te,&#160;> Te,perp&#160;(with respect to the background magnetic field) and produce nonpropagating oblique modes.&#160;Magnetic reconnection is characterized by regions of enhanced temperature anisotropy that could drive instabilities - including the electron firehose instability - affecting the particle dynamics and the energy conversion of the process. Yet, the electron firehose instability and its role in the reconnection process is still rather unexplored, especially with in situ measurements.&#160;We report MMS observations of electron firehose fluctuations observed in the exhaust region of a reconnection site in the magnetotail. The fluctuations are observed in the Earthward outflow relatively close (less than 2 di distance) to the electron diffusion region (EDR). While the characteristics of the fluctuations are compatible with oblique electron firehose fluctuations, the associated firehose instability threshold is not exceeded in the interval where the fluctuations are observed. However, the threshold is exceeded in the EDR. The wave analysis in the EDR suggests that the firehose instability could be active at the reconnection site. We suggest that the firehose fluctuations observed in the outflow region may have been originated at the EDR, where the electron temperature anisotropy exceeds the threshold values, and then advected in the outflow region.

Download Full-text

“Diffusion” region of magnetic reconnection: electron orbits and the phase space mixing

Annales Geophysicae ◽

10.5194/angeo-36-731-2018 ◽

2018 ◽

Vol 36 (3) ◽

pp. 731-740

Author(s):

Alexey P. Kropotkin

Keyword(s):

Magnetic Field ◽

Phase Space ◽

Electric Field ◽

Magnetic Reconnection ◽

Neutral Line ◽

Collisionless Plasma ◽

Uniform Electric Field ◽

Diffusion Region ◽

Finite Conductivity ◽

The Magnetic Field

Abstract. The nonlinear dynamics of electrons in the vicinity of magnetic field neutral lines during magnetic reconnection, deep inside the “diffusion” region where the electron motion is nonadiabatic, has been numerically analyzed. Test particle orbits are examined in that vicinity, for a prescribed planar two-dimensional magnetic field configuration and with a prescribed uniform electric field in the neutral line direction. On electron orbits, a strong particle acceleration occurs due to the reconnection electric field. Local instability of orbits in the neighborhood of the neutral line is pointed out. It combines with finiteness of orbits due to particle trapping by the magnetic field, and this should lead to the effect of mixing in the phase space, and the appearance of dynamical chaos. The latter may presumably be viewed as a mechanism producing finite “conductivity” in collisionless plasma near the neutral line. That conductivity is necessary to provide violation of the magnetic field frozen-in condition, i.e., for magnetic reconnection to occur in that region. Keywords. Magnetospheric physics (plasma sheet)

Download Full-text

Driving and Dissipation of Solar-Wind Turbulence: What is the Evidence?

Frontiers in Astronomy and Space Sciences ◽

10.3389/fspas.2020.611909 ◽

2021 ◽

Vol 7 ◽

Author(s):

Charles W. Smith ◽

Bernard J. Vasquez

Keyword(s):

Solar Wind ◽

Plasma Physics ◽

Thermal Plasma ◽

Collisionless Plasma ◽

Three Dimensional ◽

Density Fluctuations ◽

Plasma Dynamics ◽

Solar Wind Turbulence ◽

Close Proximity ◽

Wind Turbulence

Fifty years of solar wind observations have provided extensive data that drives an evolving view of the fundamental nature and dynamics of the magnetic, velocity, and density fluctuations that are ubiquitous throughout the heliosphere. Despite the ongoing examination of ever improving data, fundamental questions remain unanswered because there are very few multi-point measurements from a sufficient number of spacecraft in close proximity to fully resolve the three-dimensional dynamics that are at the heart of the problem. Simulations provide new insights and new questions, but most simulations sacrifice one aspect of plasma physics in order to address another. Computers and computational methods remain insufficient to simulate fully compressive, fully nonlinear, collisionless plasma dynamics with sufficient spatial range and dimension to be considered a complete description of solar wind turbulence. For these reasons, there remain multiple divergent opinions as to the underlying dynamics of solar wind turbulence, dissipation, and the observed heating of the thermal plasma. We review observations of solar wind turbulence in so far as they contribute to an understanding of solar wind heating through the existence of energy reservoirs, the dynamics that move energy from the reservoirs to the dissipation scales, and the conversion into heat of energy associated with coherent fluctuations.

Download Full-text

In situ spacecraft observations of structured electron diffusion regions during magnetic reconnection

10.5194/egusphere-egu2020-13405 ◽

2020 ◽

Author(s):

Giulia Cozzani ◽

Alessandro Retinò ◽

Francesco Califano ◽

Alexandra Alexandrova ◽

Yuri Khotyaintsev ◽

...

Keyword(s):

Magnetic Field ◽

Energy Conversion ◽

Magnetic Reconnection ◽

Rapid Heating ◽

Energy Transition ◽

Field Measurements ◽

Low Noise ◽

Diffusion Region ◽

Electron Diffusion ◽

Point Analysis

Magnetic reconnection is a fundamental energy conversion process in plasmas. It occurs in thin current sheets, where a change in the magnetic field topology leads to rapid heating of plasma, plasma bulk acceleration and acceleration of plasma particles. To allow for magnetic field reconfiguration, both ions and electrons must be demagnetized. The ion and electron demagnetization &#160;take place in the ion and electron diffusion regions respectively, in both cases at kinetic scales. For the first time, Magnetospheric Multiscale (MMS) spacecraft observations, at inter-spacecraft separation comparable to the electron inertial length, allow for a multi-point analysis of the electron diffusion region (EDR). A key question is whether the EDR has a homogeneous or patchy structure.&#160;Here we report MMS observations at the magnetopause providing evidence of inhomogeneous current densities and energy conversion over a few (&#8764; 3 de) electron inertial lengths suggesting that the EDR can be structured at electron scales. In particular, the energy conversion is patchy and changing sign in the vicinity of the reconnection site implying that the EDR comprises regions where energy is transferred from the field to the plasma and regions with the opposite energy transition, which is unexpected during reconnection. The origin of the patchy energy conversion appears to be connected to the large ve,N &#8764; ve,M directed from the magnetosphere to magnetosheath. These observations are consistent with recent high-resolution and low-noise kinetic simulations of asymmetric reconnection.&#160;Patchy energy conversion is observed also in an EDR at the magnetotail, where the inter-spacecraft separation was &#8764; 1 de. Electric field measurements are different among the spacecraft suggesting inhomogeneities at the electron scale. However, in this case the current density appear homogeneous in the EDR suggesting that the structuring may be sourced from a different kind of electron dynamics in the magnetotail.

Download Full-text

Präzisions-Forstwirtschaft – was ist das? | Precision forestry – what's that?

Schweizerische Zeitschrift fur Forstwesen ◽

10.3188/szf.2007.0235 ◽

2007 ◽

Vol 158 (8) ◽

pp. 235-242 ◽

Cited By ~ 2

Author(s):

Hans Rudolf Heinimann

Keyword(s):

Business Processes ◽

Spatial Scales ◽

Supply Chain Coordination ◽

Sensor Technology ◽

Small Scale ◽

Soil Physics ◽

Coordination Problem ◽

Precision Engineering ◽

Precision Forestry ◽

And Control

The term «precision forestry» was first introduced and discussed at a conference in 2001. The aims of this paper are to explore the scientific roots of the precision concept, define «precision forestry», and sketch the challenges that the implementation of this new concept may present to practitioners, educators, and researchers. The term «precision» does not mean accuracy on a small scale, but instead refers to the concurrent coordination and control of processes at spatial scales between 1 m and 100 km. Precision strives for an automatic control of processes. Precision land use differs from precision engineering by the requirements of gathering,storing and managing spatio-temporal variability of site and vegetation parameters. Practitioners will be facing the challenge of designing holistic, standardized business processes that are valid for whole networks of firms,and that follow available standards (e.g., SCOR, WoodX). There is a need to educate and train forestry professionals in the areas of business process re-engineering, computer supported management of business transactions,methods of remote sensing, sensor technology and control theory. Researchers will face the challenge of integrating plant physiology, soil physics and production sciences and solving the supply chain coordination problem (SCCP).

Download Full-text

Dispersal and Land Cover Contribute to Pseudorabies Virus Exposure in Invasive Wild Pigs

EcoHealth ◽

10.1007/s10393-020-01508-6 ◽

2021 ◽

Author(s):

Felipe A. Hernández ◽

Amanda N. Carr ◽

Michael P. Milleson ◽

Hunter R. Merrill ◽

Michael L. Avery ◽

...

Keyword(s):

Land Cover ◽

Disease Transmission ◽

Wildlife Conservation ◽

Pseudorabies Virus ◽

Spatial Scales ◽

Information Criterion ◽

Small Scale ◽

Wild Pigs ◽

Bacterial Agent ◽

Open Canopy

AbstractWe investigated the landscape epidemiology of a globally distributed mammal, the wild pig (Sus scrofa), in Florida (U.S.), where it is considered an invasive species and reservoir to pathogens that impact the health of people, domestic animals, and wildlife. Specifically, we tested the hypothesis that two commonly cited factors in disease transmission, connectivity among populations and abundant resources, would increase the likelihood of exposure to both pseudorabies virus (PrV) and Brucella spp. (bacterial agent of brucellosis) in wild pigs across the Kissimmee Valley of Florida. Using DNA from 348 wild pigs and sera from 320 individuals at 24 sites, we employed population genetic techniques to infer individual dispersal, and an Akaike information criterion framework to compare candidate logistic regression models that incorporated both dispersal and land cover composition. Our findings suggested that recent dispersal conferred higher odds of exposure to PrV, but not Brucella spp., among wild pigs throughout the Kissimmee Valley region. Odds of exposure also increased in association with agriculture and open canopy pine, prairie, and scrub habitats, likely because of highly localized resources within those land cover types. Because the effect of open canopy on PrV exposure reversed when agricultural cover was available, we suggest that small-scale resource distribution may be more important than overall resource abundance. Our results underscore the importance of studying and managing disease dynamics through multiple processes and spatial scales, particularly for non-native pathogens that threaten wildlife conservation, economy, and public health.

Download Full-text

PIC methods in astrophysics: simulations of relativistic jets and kinetic physics in astrophysical systems

Living Reviews in Computational Astrophysics ◽

10.1007/s41115-021-00012-0 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Kenichi Nishikawa ◽

Ioana Duţan ◽

Christoph Köhn ◽

Yosuke Mizuno

Keyword(s):

Plasma Physics ◽

Magnetic Reconnection ◽

Laser Plasma ◽

High Performance ◽

Relativistic Jets ◽

Astrophysical Plasmas ◽

Computing Power ◽

Particle In Cell ◽

The Future ◽

Pic Method

AbstractThe Particle-In-Cell (PIC) method has been developed by Oscar Buneman, Charles Birdsall, Roger W. Hockney, and John Dawson in the 1950s and, with the advances of computing power, has been further developed for several fields such as astrophysical, magnetospheric as well as solar plasmas and recently also for atmospheric and laser-plasma physics. Currently more than 15 semi-public PIC codes are available which we discuss in this review. Its applications have grown extensively with increasing computing power available on high performance computing facilities around the world. These systems allow the study of various topics of astrophysical plasmas, such as magnetic reconnection, pulsars and black hole magnetosphere, non-relativistic and relativistic shocks, relativistic jets, and laser-plasma physics. We review a plethora of astrophysical phenomena such as relativistic jets, instabilities, magnetic reconnection, pulsars, as well as PIC simulations of laser-plasma physics (until 2021) emphasizing the physics involved in the simulations. Finally, we give an outlook of the future simulations of jets associated to neutron stars, black holes and their merging and discuss the future of PIC simulations in the light of petascale and exascale computing.

Download Full-text

FORMULATION OF THE HEAT CONDUCTION EQUATION FOR HETEROGENEOUS MEDIA WITH MULTIPLE SPATIAL SCALES USING REITERATED HOMOGENIZATION

Revista de Engenharia Térmica ◽

10.5380/reterm.v15i1.62165 ◽

2016 ◽

Vol 15 (1) ◽

pp. 96

Author(s):

E. Iglesias-Rodríguez ◽

M. E. Cruz ◽

J. Bravo-Castillero ◽

R. Guinovart-Díaz ◽

R. Rodríguez-Ramos ◽

...

Keyword(s):

Heat Conduction ◽

Small Parameter ◽

Heat Conduction Equation ◽

Heterogeneous Media ◽

Spatial Scales ◽

Conduction Equation ◽

Small Scale ◽

Multiple Spatial Scales ◽

Effective Coefficients ◽

Reiterated Homogenization

Heterogeneous media with multiple spatial scales are finding increased importance in engineering. An example might be a large scale, otherwise homogeneous medium filled with dispersed small-scale particles that form aggregate structures at an intermediate scale. The objective in this paper is to formulate the strong-form Fourier heat conduction equation for such media using the method of reiterated homogenization. The phases are assumed to have a perfect thermal contact at the interface. The ratio of two successive length scales of the medium is a constant small parameter ε. The method is an up-scaling procedure that writes the temperature field as an asymptotic multiple-scale expansion in powers of the small parameter ε . The technique leads to two pairs of local and homogenized equations, linked by effective coefficients. In this manner the medium behavior at the smallest scales is seen to affect the macroscale behavior, which is the main interest in engineering. To facilitate the physical understanding of the formulation, an analytical solution is obtained for the heat conduction equation in a functionally graded material (FGM). The approach presented here may serve as a basis for future efforts to numerically compute effective properties of heterogeneous media with multiple spatial scales.

Download Full-text