scholarly journals The Parker problem: existence of smooth force-free fields and coronal heating

2020 ◽  
Vol 17 (1) ◽  
Author(s):  
David I. Pontin ◽  
Gunnar Hornig
Keyword(s):  
Magnetic Field ◽  
Coronal Heating ◽  
Plasma Parameters ◽  
Astrophysical Plasmas ◽  
Plasma Dynamics ◽  
Open Questions ◽  
Free Fields ◽  
Field Lines ◽  
The Many ◽  
Ideal Plasma

AbstractParker (Astrophys J 174:499, 1972) put forward a hypothesis regarding the fundamental nature of equilibrium magnetic fields in astrophysical plasmas. He proposed that if an equilibrium magnetic field is subjected to an arbitrary, small perturbation, then—under ideal plasma dynamics—the resulting magnetic field will in general not relax towards a smooth equilibrium, but rather, towards a state containing tangential magnetic field discontinuities. Even at astrophysical plasma parameters, as the singular state is approached dissipation must eventually become important, leading to the onset of rapid magnetic reconnection and energy dissipation. This topological dissipation mechanism remains a matter of debate, and is a key ingredient in the nanoflare model for coronal heating. We review the various theoretical and computational approaches that have sought to prove or disprove Parker’s hypothesis. We describe the hypothesis in the context of coronal heating, and discuss different approaches that have been taken to investigating whether braiding of magnetic field lines is responsible for maintaining the observed coronal temperatures. We discuss the many advances that have been made, and highlight outstanding open questions.

HelioSwarm: The Nature of Turbulence in Space Plasmas

2021 ◽  
Author(s):  
Harlan Spence ◽  
Kristopher Klein ◽  
HelioSwarm Science Team
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Large Scale ◽  
Solar Wind Plasma ◽  
Turbulent Energy ◽  
Space Plasmas ◽  
Plasma Parameters ◽  
Astrophysical Plasmas ◽  
Ion Distributions ◽  
Background Magnetic Field

<p>Recently selected for phase A study for NASA’s Heliophysics MidEx Announcement of Opportunity, the HelioSwarm Observatory proposes to transform our understanding of the physics of turbulence in space and astrophysical plasmas by deploying nine spacecraft to measure the local plasma and magnetic field conditions at many points, with separations between the spacecraft spanning MHD and ion scales.  HelioSwarm resolves the transfer and dissipation of turbulent energy in weakly-collisional magnetized plasmas with a novel configuration of spacecraft in the solar wind. These simultaneous multi-point, multi-scale measurements of space plasmas allow us to reach closure on two science goals comprised of six science objectives: (1) reveal how turbulent energy is transferred in the most probable, undisturbed solar wind plasma and distributed as a function of scale and time; (2) reveal how this turbulent cascade of energy varies with the background magnetic field and plasma parameters in more extreme solar wind environments; (3) quantify the transfer of turbulent energy between fields, flows, and ion heat; (4) identify thermodynamic impacts of intermittent structures on ion distributions; (5) determine how solar wind turbulence affects and is affected by large-scale solar wind structures; and (6) determine how strongly driven turbulence differs from that in the undisturbed solar wind. </p>

scholarly journals The development of magnetic field line wander by plasma turbulence

2017 ◽  
Vol 83 (4) ◽  
Author(s):  
Gregory G. Howes ◽  
Sofiane Bourouaine
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
Large Scale ◽  
Magnetic Energy ◽  
Plasma Turbulence ◽  
Alfven Wave ◽  
Astrophysical Plasmas ◽  
Field Lines ◽  
The Magnetic Field

Plasma turbulence occurs ubiquitously in space and astrophysical plasmas, mediating the nonlinear transfer of energy from large-scale electromagnetic fields and plasma flows to small scales at which the energy may be ultimately converted to plasma heat. But plasma turbulence also generically leads to a tangling of the magnetic field that threads through the plasma. The resulting wander of the magnetic field lines may significantly impact a number of important physical processes, including the propagation of cosmic rays and energetic particles, confinement in magnetic fusion devices and the fundamental processes of turbulence, magnetic reconnection and particle acceleration. The various potential impacts of magnetic field line wander are reviewed in detail, and a number of important theoretical considerations are identified that may influence the development and saturation of magnetic field line wander in astrophysical plasma turbulence. The results of nonlinear gyrokinetic simulations of kinetic Alfvén wave turbulence of sub-ion length scales are evaluated to understand the development and saturation of the turbulent magnetic energy spectrum and of the magnetic field line wander. It is found that turbulent space and astrophysical plasmas are generally expected to contain a stochastic magnetic field due to the tangling of the field by strong plasma turbulence. Future work will explore how the saturated magnetic field line wander varies as a function of the amplitude of the plasma turbulence and the ratio of the thermal to magnetic pressure, known as the plasma beta.

Theory and observations of switchbacks’ evolution in the solar wind

2021 ◽  
Author(s):  
Anna Tenerani ◽  
Marco Velli ◽  
Lorenzo Matteini
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Radial Magnetic Field ◽  
Open Questions ◽  
Coronal Activity ◽  
Turbulent Heating ◽  
Field Lines ◽  
Radial Evolution ◽  
Field Correlation

<p>Alfvénic fluctuations represent the dominant contributions to turbulent fluctuations in the solar wind, especially, but not limited to, the fastest streams with velocity of the order of 600-700 km/s. Alfvénic fluctuations can contribute to solar wind heating and acceleration via wave pressure and turbulent heating. Observations show that such fluctuations are characterized by a nearly constant magnetic field amplitude, a condition which remains largely to be understood and that may be an indication of how fluctuations evolve and relax in the expanding solar wind. Interestingly, measurements from Parker Solar Probe have shown the ubiquitous and persistent presence of the so-called switchbacks. These are magnetic field lines which are strongly perturbed to the point that they produce local inversions of the radial magnetic field. The corresponding signature of switchbacks in the velocity field is that of local enhancements in the radial speed (or jets) that display the typical velocity-magnetic field correlation that characterizes Alfvén waves propagating away from the Sun. While there is not yet a general consensus on what is the origin of switchbacks and their connection to coronal activity, a first necessary step to answer these important questions is to understand how they evolve and how long they can persist in the solar wind. Here we investigate the evolution of switchbacks. We address how their evolution is affected by parametric instabilities and the possible role of expansion, by comparing models with the observed radial evolution of the fluctuations’ amplitude. We finally discuss what are the implications of our results for models of switchback generation and related open questions.</p>

Coronal Heating through Braiding of Magnetic Field Lines

2004 ◽  
Vol 617 (1) ◽  
pp. L85-L88 ◽  
Author(s):  
Hardi Peter ◽  
Boris V. Gudiksen ◽  
Åke Nordlund
Keyword(s):  
Magnetic Field ◽  
Coronal Heating ◽  
Field Lines

scholarly journals Investigation on High Velocity Plasmas and Field Aligned Currents at High Latitudes

2020 ◽  
pp. 22-29
Author(s):  
J. C. K. Akhila ◽  
C. P. Anil Kumar
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
High Velocity ◽  
Transmission Function ◽  
External Loading ◽  
Plasma Parameters ◽  
Spherical Cap ◽  
Field Aligned Current ◽  
Field Lines ◽  
Spherical Cap Harmonic Analysis

The interaction of high velocity plasma with Earth’s magnetic field is fundamental and offer many questions on high latitude electrodynamics. The problems associated with influence of electric field and Field Aligned Current (FAC) generation is investigated with the aid of spherical cap harmonic analysis at 830 Mag. Lat. in southern hemispheres. The investigation is done on the cases with different Interplanetary Magnetic Field (IMF) conditions after the earth directed solar events. The helio-plasma parameters viz., density, velocity, energy, electron temperature are also noted during the field aligned current studies. It seems that, due to external magnetic field influence polarization of plasma electric field take place (reorientation of the convective cells). It happens with different orientation as per the magnitude and direction of By and Bz component and the horizontal currents. It is noted that the FAC value also depends on kinetic energy of the plasma streams and conductivity of external loading. As the plasma decelerates by force Jsw X Esw, the resultant current may extend along the field lines. Increases in the FAC density are seemed to be proportional to the transmission function.

Kinetics of Fast Component and Energy Balance of the Plasma in Gas Dynamic System With Solenoidal Magnetic Field

2010 ◽  
Author(s):  
Alexei Chirkov ◽  
Sergey Kaskov
Keyword(s):  
Magnetic Field ◽  
Collision Operator ◽  
High Energy ◽  
Plasma Parameters ◽  
Magnetic Mirrors ◽  
Gas Dynamic ◽  
Barrier Formation ◽  
Maxwellian Plasma ◽  
Field Lines ◽  
Fast Ion

Numerical model of ion kinetics is considered for the axially symmetrical magnetic trap. Magnetic system of the trap consists of long solenoid and two end coils which constrict magnetic field lines and form so-called magnetic mirrors reflecting charged particles. The trap contains warm Maxwellian plasma and strongly non-Maxwellian high-energy (fast) ions. Steady-state fast ion population supported by the ionization of high-energy neutral atoms injected into the plasma. Physical model is based on the kinetic equation with two-dimensional Fokker–Planck collision operator in the velocity phase space. Regimes of plasma exhaust trough the mirrors are considered taking into account possibility of electrostatic barrier formation. Such regimes essentially differ from gas dynamic exhaust of the warm Maxwellian plasma. Parameters of power balance for the system under consideration are discussed.

scholarly journals Coronal Heating Topology: The Interplay of Current Sheets and Magnetic Field Lines

2017 ◽  
Vol 844 (1) ◽  
pp. 87 ◽  
Author(s):  
A. F. Rappazzo ◽  
W. H. Matthaeus ◽  
D. Ruffolo ◽  
M. Velli ◽  
S. Servidio
Keyword(s):  
Magnetic Field ◽  
Coronal Heating ◽  
Current Sheets ◽  
Field Lines

Detailed analytical investigation of magnetic field line random walk in turbulent plasmas: I. Two-component slab/two-dimensional turbulence

2008 ◽  
Vol 74 (5) ◽  
pp. 657-677 ◽  
Author(s):  
I. KOURAKIS ◽  
A. SHALCHI
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Mean Square Displacement ◽  
Analytical Investigation ◽  
Asymptotic Result ◽  
Two Dimensional ◽  
Plasma Parameters ◽  
Diffusive Regime ◽  
Two Component ◽  
Field Lines

AbstractThe random displacement of magnetic field lines in the presence of magnetic turbulence in plasmas is investigated from first principles. A two-component (slab/two-dimensional composite) model for the turbulence spectrum is employed. An analytical investigation of the asymptotic behavior of the field-line mean square displacement (FL-MSD) is carried out. It is shown that the magnetic field lines behave superdiffusively for very large values of the position variable z, since the FL-MSD σ varies as σ ~ z4/3. An intermediate diffusive regime may also possibly exist for finite values of z under conditions which are explicitly determined in terms of the intrinsic turbulent plasma parameters. The superdiffusive asymptotic result is confirmed numerically via an iterative algorithm. The relevance to previous results is discussed.

scholarly journals Onset of fast magnetic reconnection and particle energization in laboratory and space plasmas

2020 ◽  
Vol 86 (6) ◽  
Author(s):  
F. Pucci ◽  
M. Velli ◽  
C. Shi ◽  
K. A. P. Singh ◽  
A. Tenerani ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Magnetic Reconnection ◽  
Theoretical Models ◽  
Laboratory Plasma ◽  
Plasma Parameters ◽  
Astrophysical Plasmas ◽  
Plasma Dynamics ◽  
Laboratory Plasmas ◽  
Wide Range ◽  
Kinetic Effects

The onset of magnetic reconnection in space, astrophysical and laboratory plasmas is reviewed discussing results from theory, numerical simulations and observations. After a brief introduction on magnetic reconnection and approach to the question of onset, we first discuss recent theoretical models and numerical simulations, followed by observations of reconnection and its effects in space and astrophysical plasmas from satellites and ground-based detectors, as well as measurements of reconnection in laboratory plasma experiments. Mechanisms allowing reconnection spanning from collisional resistivity to kinetic effects as well as partial ionization are described, providing a description valid over a wide range of plasma parameters, and therefore applicable in principle to many different astrophysical and laboratory environments. Finally, we summarize the implications of reconnection onset physics for plasma dynamics throughout the Universe and illustrate how capturing the dynamics correctly is important to understanding particle acceleration. The goal of this review is to give a view on the present status of this topic and future interesting investigations, offering a unified approach.

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