scholarly journals Simulation study on parametric dependence of whistler-mode hiss generation in the plasmasphere

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Yin Liu ◽  
Yoshiharu Omura ◽  
Mitsuru Hikishima
Keyword(s):  
Magnetic Field ◽  
Electron Density ◽  
Nonlinear Process ◽  
Background Field ◽  
Realistic Model ◽  
Equatorial Region ◽  
Generation Process ◽  
Hot Electron ◽  
Wave Growth ◽  
Background Magnetic Field

AbstractWe conduct electromagnetic particle simulations to examine the applicability of nonlinear wave growth theory to the generation process of plasmaspheric hiss. We firstly vary the gradient of the background magnetic field from a realistic model to a rather steep gradient model. Under such variation, the threshold amplitude in the nonlinear theory increases quickly and the overlap between threshold and optimum amplitude disappears correspondingly, the nonlinear process is suppressed. In the simulations, as we enlarge the gradient coefficient of the background magnetic field, waves generated near the equator do not grow through propagation. By examining the range of suitable values of inhomogeneity factor S (i.e., $$|S|<2$$ | S | < 2 ), we find the generation of wave packets is limited to the equatorial region when the background field is steep, showing a good agreement with what is indicated by critical distance in the theory. We then check the dependence of generation of hiss emissions on different hot electron densities. Since the overlap between threshold and optimum amplitude vanishes, the nonlinear process is weakened when hot electron density becomes smaller. In the simulation results, we find similar wave structures in all density cases, yet with different magnitudes. The existence of suitable S values implies that the nonlinear process occurs even at a low level of hot electron density. However, by examining $$J_E$$ J E that closely relates to the wave growth, we find energy conveyed from particles to waves is much limited in small density cases. Therefore, the nonlinear process is suppressed when hot electron density is small, which agrees with the theoretical analysis. Graphical Abstract

scholarly journals Simulation Study on Parametric Dependence of Whistler-mode Hiss Generation in the Plasmasphere

2021 ◽  
Author(s):  
Yin Liu ◽  
Yoshiharu Omura ◽  
Mitsuru Hikishima
Keyword(s):  
Electron Density ◽  
Wave Packets ◽  
Nonlinear Process ◽  
Background Field ◽  
Realistic Model ◽  
Equatorial Region ◽  
Generation Process ◽  
Hot Electron ◽  
Wave Growth ◽  
Background Magnetic Field

Abstract We conduct electromagnetic particle simulations to examine the applicability of nonlinear wave growth theory to the generation process of plasmaspheric hiss. We firstly vary the gradient of background magnetic field from a realistic model to a rather steep gradient model. Under such variation, the threshold amplitude in the nonlinear theory increases quickly and the overlap between threshold and optimum amplitude disappears correspondingly, and the nonlinear process is suppressed. In the simulations, as we enlarge the gradient variation of the background magnatic field, waves generated near the equator do not grow through propagation. By examining extracted typical wave packets from different gradient cases, we find the generation of wave packets is limited to equatorial region when background field is steep, showing a good agreement with what is indicated by critical distance in the theory. We then check the dependence of generation of hiss emissions on different hot electron densities. Since the overlap between threshold and optimum amplitude vanishes, the nonlinear process is weakened when hot electron density becomes smaller. In the simulation results, we find similar wave structures in all density cases, yet with different magnitudes. The existence of suitable values of the inhomogeneity factor S implies that nonlinear process occurs even at a low level of hot electron density. However, by examining J E which is closely related to the wave growth, we find energy conveyed from particles to waves is much limited in small density cases. Therefore, the nonlinear process is suppressed when hot electron density is small, which is in agreement with the theoretical analysis.

scholarly journals Multi-spacecraft determination of wave characteristics near the proton gyrofrequency in high-altitude cusp

2005 ◽  
Vol 23 (3) ◽  
pp. 983-995 ◽  
Author(s):  
D. Sundkvist ◽  
A. Vaivads ◽  
M. André ◽  
J.-E. Wahlund ◽  
Y. Hobara ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Altitude ◽  
Nonlinear Effects ◽  
Linear Wave ◽  
Wave Growth ◽  
Ion Cyclotron Waves ◽  
Background Magnetic Field ◽  
Ion Cyclotron ◽  
The Waves ◽  
Proton Gyrofrequency

Abstract. We present a detailed study of waves with frequencies near the proton gyrofrequency in the high-altitude cusp for northward IMF as observed by the Cluster spacecraft. Waves in this regime can be important for energization of ions and electrons and for energy transfer between different plasma populations. These waves are present in the entire cusp with the highest amplitudes being associated with localized regions of downward precipitating ions, most probably originating from the reconnection site at the magnetopause. The Poynting flux carried by these waves is downward/upward at frequencies below/above the proton gyrofrequency, which is consistent with the waves being generated near the local proton gyrofrequency in an extended region along the flux tube. We suggest that the waves can be generated by the precipitating ions that show shell-like distributions. There is no clear polarization of the perpendicular wave components with respect to the background magnetic field, while the waves are polarized in a parallel-perpendicular plane. The coherence length is of the order of one ion-gyroradius in the direction perpendicular to the ambient magnetic field and a few times larger or more in the parallel direction. The perpendicular phase velocity was found to be of the order of 100km/s, an order of magnitude lower than the local Alfvén speed. The perpendicular wavelength is of the order of a few proton gyroradius or less. Based on our multi-spacecraft observations we conclude that the waves cannot be ion-whistlers, while we suggest that the waves can belong to the kinetic Alfvén branch below the proton gyrofrequency fcp and be described as non-potential ion-cyclotron waves (electromagnetic ion-Bernstein waves) above. Linear wave growth calculations using kinetic code show considerable wave growth of non-potential ion cyclotron waves at wavelengths agreeing with observations. Inhomogeneities in the plasma on the order of the ion-gyroradius suggests that inhomogeneous (drift) or nonlinear effects or both of these should be taken into account.

scholarly journals Europa's Alfvén wing: shrinkage and displacement influenced by an induced magnetic field

2007 ◽  
Vol 25 (4) ◽  
pp. 905-914 ◽  
Author(s):  
M. Volwerk ◽  
K. Khurana ◽  
M. Kivelson
Keyword(s):  
Magnetic Field ◽  
Plasma Density ◽  
Geometric Modeling ◽  
Numerical Models ◽  
Background Field ◽  
Entry And Exit ◽  
Induced Magnetic Field ◽  
Background Magnetic Field ◽  
Magnetometer Data ◽  
Induced Field

Abstract. The Galileo magnetometer data are used to investigate the structure of the Alfvén wing during three flybys of Europa. The presence of an induced magnetic field is shown to shrink the cross section of the Alfvén wing and offset it along the direction radial to Jupiter. Both the shrinkage and the offset depend on the strength of the induced field. The entry and exit points of the spacecraft into and out of the Alfvén wings are modeled to determine the angle between the wings and the background magnetic field. Tracing of the Alfvén characteristics in a model magnetic field consisting of Jupiter's background field and an induced field in Europa produces an offset and shrinking of the Alfvén wing consistent with the geometric modeling. Thus we believe that the Alfvén wing properties have been determined correctly. The Alfvén wing angle is directly proportional to the local Alfvén velocity, and is thus a probe for the local plasma density. We show that the inferred plasma density can be understood in terms of the electron density measured by the plasma wave experiment. When Europa is located in the Jovian plasma sheet the derived mass-per-charge exceeds the previous estimates, which is a result of increased pickup of sputtered ions near the moon. The estimated rate of O2+ pickup agrees well with the results from numerical models.

Particle acceleration by interstellar plasma shock waves in non-uniform background magnetic field

2020 ◽  
Vol 498 (4) ◽  
pp. 5517-5523
Author(s):  
P Rashed-Mohassel ◽  
M Ghorbanalilu
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Shock Waves ◽  
Electric Field ◽  
Background Field ◽  
Magnetized Plasma ◽  
Background Magnetic Field ◽  
Positive Variation ◽  
Uniform Background ◽  
Plasma Shock

ABSTRACT Particle acceleration by plasma shock waves is investigated for a magnetized plasma cloud propagating in a non-uniform background magnetic field by means of analytical and numerical calculations. The mechanism studied here is mainly, magnetic trapping acceleration (MTA) which is previously investigated for a cloud moving through the uniform interstellar magnetic field (IMF). In this work, the acceleration is studied for a cloud moving in an antiparallel background field with spatial variations along the direction of motion. For negative variation, the cloud moves towards an antiparallel magnetic field with an increasing intensity, the trapped particle moves to locations with higher convective electric field and therefore gains more energy over time. For positive variation, the background field decreases to zero and changes into a parallel field with an increasing intensity. It is concluded that, when the background field vanishes, the MTA mechanism ceases and the particle escapes into the space. This leads to a bouncing acceleration which further increases energy of the gyrating particle. The two processes are followed by a shock drift acceleration, where due to the background magnetic field gradient, the particle drifts along the electric field and gains energy. Although for positive variation, three different mechanisms are involved, energy gain is less than in the case of a uniform background field.

scholarly journals PHOTON PROPAGATION IN A MAGNETIZED MEDIUM

2002 ◽  
Vol 17 (06n07) ◽  
pp. 1055-1058 ◽  
Author(s):  
SUSHAN KONAR
Keyword(s):  
Magnetic Field ◽  
Background Field ◽  
Photon Absorption ◽  
Polarization Tensor ◽  
Finite Temperature Field Theory ◽  
Photon Propagation ◽  
Time Formalism ◽  
Background Magnetic Field ◽  
Absorption Probabilities ◽  
Real Time Formalism

Using the real time formalism of the finite temperature field theory we calculate the 1-loop polarization tensor in the presence of a background magnetic field in a medium. The expression is obtained to linear order in the background field strength. We discuss the Faraday rotation as well as the photon absorption probabilities in this context.

Magnetic Field

2013 ◽  
Author(s):  
Gary A. Glatzmaier
Keyword(s):  
Magnetic Field ◽  
Dispersion Relation ◽  
Background Field ◽  
Magnetohydrodynamic Equations ◽  
Electrically Conducting ◽  
Background Magnetic Field ◽  
Nonlinear Simulations ◽  
Uniform Background ◽  
The Stability ◽  
2D Model

This chapter focuses on magnetoconvection, which refers to thermal convection of an electrically conducting fluid within a background magnetic field maintained by some external mechanism. It first provides a brief overview of magnetohydrodynamics and the magnetohydrodynamic equations before explaining how to make a 2D model of magnetic field. In this approach, the case of a uniform vertical background field and the case of a uniform horizontal background field are both considered. The chapter then describes how one could simulate a case of a uniform background field that is tilted relative to both the vertical and horizontal axes. It also considers what can be learned about the stability and structure of magnetoconvection and the dispersion relation for magneto-gravity waves from analytical analyses without the nonlinear terms. Finally, it discusses nonlinear simulations of magnetoconvection in a box with impermeable side boundaries, along with magnetoconvection with a horizontal background field and an arbitrary background field.

On the existence of transverse MHD oscillations in an inhomogeneous magnetoplasma

1990 ◽  
Vol 43 (1) ◽  
pp. 83-99 ◽  
Author(s):  
Andrew N. Wright
Keyword(s):  
Magnetic Field ◽  
Three Dimensional ◽  
Background Field ◽  
Alfven Wave ◽  
Field Perturbation ◽  
Independent Field ◽  
Background Magnetic Field ◽  
Field Geometry ◽  
Divergence Free ◽  
Field Lines

In a cold plasma with no compressional field perturbation the equations governing the two perpendicular components of magnetic-field perturbation decouple. These two equations depend only upon spatial derivatives along the background magnetic field, and give the impression of independent field-line motion in the two transverse directions. However, the perturbation magnetic field b must be divergence-free. It is not meaningful to ask if the field perturbation on an individual background line of force satisfies ∇. b = 0. To decide whether b is divergence-free, we need to know about its spatial variation, i.e. what the state of the neighbouring field lines is. In this paper we investigate two classes of solutions: first we allow the perturbation magnetic flux to satisfy ∇. b = 0 by threading across the background lines of force; the second solution closes b by allowing the perturbation flux to encircle the background field lines (torsional Alfvén waves). For both of these solutions we study the relationship between neighbouring field lines, and are able to derive a set of criteria that the background medium must satisfy. For both classes we find restrictions upon the background magnetic-field geometry - the first class also has a constraint upon the plasma density. The introduction of perfectly conducting massive boundaries is also considered, and a relation given that they must satisfy if the field perturbation is to remain transverse. The criteria are presented in such a manner that it is easy to test if a given medium will be able to support the solutions described above. For example, a three-dimensional dipolo geometry is able to carry oscillatory toroidal fields; but not purely poloidal ones or a torsional Alfvén wave.

scholarly journals Background field Landau mode operators for the nucleon

2018 ◽  
Vol 175 ◽  
pp. 05018 ◽  
Author(s):  
Waseem Kamleh ◽  
Ryan Bignell ◽  
Derek B. Leinweber ◽  
Matthias Burkardt
Keyword(s):  
Magnetic Field ◽  
Correlation Function ◽  
Charged Particle ◽  
Finite Lattice ◽  
Background Field ◽  
Spatial Symmetry ◽  
Preliminary Results ◽  
Mode Effects ◽  
Background Magnetic Field ◽  
Uniform Background

The introduction of a uniform background magnetic field breaks threedimensional spatial symmetry for a charged particle and introduces Landau mode effects. Standard quark operators are inefficient at isolating the nucleon correlation function at nontrivial field strengths. We introduce novel quark operators constructed from the twodimensional Laplacian eigenmodes that describe a charged particle on a finite lattice. These eigenmode-projected quark operators provide enhanced precision for calculating nucleon energy shifts in a magnetic field. Preliminary results are obtained for the neutron and proton magnetic polarisabilities using these methods.

scholarly journals THE NEUTRINO SELF-ENERGY IN A MAGNETIZED MEDIUM

2008 ◽  
Vol 23 (32) ◽  
pp. 2771-2786 ◽  
Author(s):  
ALBERTO BRAVO GARCÍA ◽  
KAUSHIK BHATTACHARYA ◽  
SARIRA SAHU
Keyword(s):  
Magnetic Field ◽  
W Boson ◽  
Background Field ◽  
The Self ◽  
Boson Mass ◽  
Gauge Fields ◽  
Self Energy ◽  
Background Magnetic Field ◽  
Boson Propagator ◽  
Charged Leptons

In this work we calculate the neutrino self-energy in the presence of a magnetized medium. The magnetized medium consists of electrons, positrons, neutrinos and a uniform classical magnetic field. The calculation is done assuming that the background magnetic field is weak compared to the W-boson mass squared, as a consequence of which only linear order corrections in the field are included in the W-boson propagator. The electron propagator consists of all order corrections in the background field. Although the neutrino self-energy in a magnetized medium in various limiting cases has been calculated previously, in this paper we produce the most general expression of the self-energy in the absence of the Landau quantization of the charged gauge fields. We calculate the effect of the Landau quantization of the charged leptons on the neutrino self-energy in the general case. Our calculation is specifically suited for situations where the background plasma may be CP symmetric.

scholarly journals Longitudinal drift of Tayler instability eigenmodes as a possible explanation for super-slowly rotating Ap stars

2020 ◽  
Vol 638 ◽  
pp. L9
Author(s):  
L. L. Kitchatinov ◽  
I. S. Potravnov ◽  
A. A. Nepomnyashchikh
Keyword(s):  
Magnetic Field ◽  
Drift Rate ◽  
Background Field ◽  
Slow Rotation ◽  
Rotation Periods ◽  
Background Magnetic Field ◽  
Rotating Reference Frame ◽  
Thermal Patterns ◽  
Ap Stars ◽  
Rotational Direction

Context. Rotation periods inferred from the magnetic variability of some Ap stars are incredibly long, exceeding ten years in some cases. An explanation for such slow rotation is lacking. Aims. This paper attempts to provide an explanation of the super-slow rotation of the magnetic and thermal patterns of Ap stars in terms of the longitudinal drift of the unstable disturbances of the kink-type (Tayler) instability of their internal magnetic field. Methods. The rates of drift and growth were computed for eigenmodes of Tayler instability using stellar parameters estimated from a structure model of an A star. The computations refer to the toroidal background magnetic field of varied strength. Results. The non-axisymmetric unstable disturbances drift in a counter-rotational direction in the co-rotating reference frame. The drift rate increases with the strength of the background field. For a field strength exceeding the (equipartition) value of equal Alfven and rotational velocities, the drift rate approaches the proper rotation rate of a star. The eigenmodes in an inertial frame show very slow rotation in this case. Patterns of magnetic and thermal disturbances of the slowly rotating eigenmodes are also computed. Conclusions. The counter-rotational drift of Tayler instability eigenmodes is a possible explanation for the observed phenomenon of super-slowly rotating Ap stars.

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