Characteristics of the Pitch-Angle Anisotropy of Energetic Protons in the Daytime Magnetosphere due to Particle Drift in the Nondipole Magnetic Field

Controlling a swarm of microrobots with external fields is one of the major challenges for untethered microrobots. In this work, we present a new method to generate a vortex-like paramagnetic nanoparticle swarm (VPNS) from dispersed nanoparticles with a diameter of 500 nm, using rotating magnetic fields. The VPNS exhibits a dynamic-equilibrium structure, in which the nanoparticles perform synchronized motions. The mechanisms of the pattern-generation process are analyzed, simulated, and validated by experiments. By tuning the rotating frequency of the input magnetic field, the pattern of a VPNS changes accordingly. Analytical models for estimating the areal change of the pattern are proposed, and they have good agreement with the experimental data. Moreover, reversible merging and splitting of vortex-like swarms are demonstrated and investigated. Serving as a mobile robotic end-effector, a VPNS is capable of making locomotion by tuning the pitch angle of the actuating rotating field. With a small pitch angle, e.g. 2°, the whole swarm moves as an entity, and the shape of the pattern remains intact. In addition, the trapping forces of VPNSs are verified, showing the critical input parameters of the magnetic field that affect the morphology of the swarm. Finally, we demonstrate that VPNSs pass through curved and branched channels with high positioning precision, and the access rates for targeted delivery are over 90%, which are significantly higher than those in the cases of particle swarms moving with tumbling motions.

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Excitation And Ionization By Auroral Protons

Australian Journal of Physics ◽

10.1071/ph660309 ◽

1966 ◽

Vol 19 (3) ◽

pp. 309 ◽

Cited By ~ 30

Keyword(s):

Magnetic Field ◽

Energy Range ◽

Pitch Angle ◽

Proton Energy ◽

Ionization Rate ◽

Energy Spectra ◽

Proton Fluxes ◽

Atmospheric Ionization ◽

The Magnetic Field

Height distributions are presented for the atmospheric ionization rate and Balmer radiation resulting from precipitation of auroral protons. These results have been computed assuming proton fluxes with several different energy spectra and pitch-angle distributions about the magnetic field, the total proton energy range being restricted to 1-1000 keY.

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Pitch angle scattering of an energetic magnetized particle by a circularly polarized electromagnetic wave

10.5194/egusphere-egu21-1932 ◽

2021 ◽

Author(s):

Paul M. Bellan

Keyword(s):

Magnetic Field ◽

Electromagnetic Wave ◽

Kinetic Energy ◽

Potential Energy ◽

Pitch Angle ◽

Energetic Electron ◽

Circularly Polarized ◽

Angle Scattering ◽

Background Magnetic Field ◽

Pseudo Potential

The interaction between a circularly polarized electromagnetic wave and an energetic gyrating particle is described [1] using a relativistic pseudo-potential that is a function of the frequency mismatch,&#160; a measure of the extent to which &#969;-kzvz=&#937;/&#947; is not true. The description of this wave-particle interaction involves a sequence of relativistic transformations that ultimately demonstrate that the pseudo potential energy of a pseudo particle adds to a pseudo kinetic energy giving a total pseudo energy that is a constant of the motion. The pseudo kinetic energy is proportional to the square of the particle acceleration (compare to normal kinetic energy which is the square of a velocity) and the pseudo potential energy is a function of the mismatch and so effectively a function of the particle velocity parallel to the background magnetic field (compare to normal potential energy which is a function of position). Analysis of the pseudo-potential provides a means for interpreting particle motion in the wave in a manner analogous to the analysis of a normal particle bouncing in a conventional potential well.&#160; The wave-particle&#160; interaction is electromagnetic and so differs from and is more complicated than the well-known Landau damping of electrostatic waves.&#160; The pseudo-potential profile depends on the initial mismatch, the normalized wave amplitude, and the initial angle between the wave magnetic field and the particle perpendicular velocity. For zero initial mismatch, the pseudo-potential consists of only one valley, but for finite mismatch, there can be two valleys separated by a hill. A large pitch angle scattering of the energetic electron can occur in the two-valley situation but fast scattering can also occur in a single valley. Examples relevant to magnetospheric whistler waves are discussed. Extension to the situation of a distribution of relativistic particles is presented in a companion talk [2].[1] P. M. Bellan, Phys. Plasmas 20, Art. No. 042117 (2013)[2] Y. D. Yoon and P. M. Bellan, JGR 125, Art. No. e2020JA027796 (2020)

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First in situ evidence of electron pitch angle scattering due to magnetic field line curvature in the Ion diffusion region

Journal of Geophysical Research Space Physics ◽

10.1002/2016ja022409 ◽

2016 ◽

Vol 121 (5) ◽

pp. 4103-4110 ◽

Cited By ~ 5

Author(s):

Y. C. Zhang ◽

C. Shen ◽

A. Marchaudon ◽

Z. J. Rong ◽

B. Lavraud ◽

...

Keyword(s):

Magnetic Field ◽

Field Line ◽

Magnetic Field Line ◽

Pitch Angle ◽

Diffusion Region ◽

Ion Diffusion ◽

Angle Scattering

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Helical Magnetic Cavities: Kinetic Model and Comparison with MMS Observations

10.5194/egusphere-egu21-8905 ◽

2021 ◽

Author(s):

Jinghuan Li ◽

Xuzhi Zhou ◽

Fan Yang ◽

Anton V. Artemyev ◽

Qiugang Zong

Keyword(s):

Magnetic Field ◽

Kinetic Model ◽

Pitch Angle ◽

Maxwell Equations ◽

Equilibrium Solution ◽

Space Plasma ◽

Azimuthal Magnetic Field ◽

Particle Distributions ◽

Multi Scale ◽

Self Consistent

Magnetic cavities are sudden depressions of magnetic field strength widely observed in the space plasma environments, which are often accompanied by plasma density and pressure enhancement. To describe these cavities, a self-consistent kinetic model has been proposed as an equilibrium solution to the Vlasov-Maxwell equations. However, observations from the Magnetospheric Multi-Scale (MMS) constellation have shown the existence of helical magnetic cavities characterized by the presence of azimuthal magnetic field, which could not be reconstructed by the aforementioned model. Here, we take into account another invariant of motion, the canonical axial momentum, to construct the particle distributions and accordingly modify the equilibrium model. The reconstructed magnetic cavity shows excellent agreement with the MMS1 observations not only in the electromagnetic field and plasma moment profiles but also in electron pitch-angle distributions. With the same set of parameters, the model also predicts signatures of the neighboring MMS3 spacecraft, matching its observations satisfactorily.

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Particle-In-Cell simulations of resonant interactions between whistler waves and electrons in the near-Sun solar wind: scattering of the strahl into the halo and heat flux regulation.

10.5194/egusphere-egu21-10198 ◽

2021 ◽

Author(s):

Alfredo Micera ◽

Andrei Zhukov ◽

Rodrigo A. López ◽

Maria Elena Innocenti ◽

Marian Lazar ◽

...

Keyword(s):

Magnetic Field ◽

Heat Flux ◽

Solar Wind ◽

Velocity Distribution ◽

Pitch Angle ◽

Electron Velocity ◽

Magnetic Field Direction ◽

Whistler Waves ◽

Electron Velocity Distribution ◽

Particle In Cell

Electron velocity distribution functions, initially composed of core and strahl populations as typically encountered in the near-Sun solar wind and as recently observed by Parker Solar Probe, have been modeled via fully kinetic Particle-In-Cell simulations. It has been demonstrated that, as a consequence of the evolution of the electron velocity distribution function, two branches of the whistler heat flux instability can be excited, which can drive whistler waves propagating in the direction parallel or oblique to the background magnetic field. First, the strahl undergoes pitch-angle scattering with oblique whistler waves, which provokes the reduction of the strahl drift velocity and the simultaneous broadening of its pitch angle distribution. Moreover, the interaction with the oblique whistler waves results in the scattering towards higher perpendicular velocities of resonant strahl electrons and in the appearance of a suprathermal halo population which, at higher energies, deviates from the Maxwellian distribution. Later on, the excited whistler waves shift towards smaller angles of propagation and secondary scattering processes with quasi-parallel whistler waves lead to a redistribution of the scattered particles into a more symmetric halo. All processes are accompanied by a significant decrease of the heat flux carried by the strahl population along the magnetic field direction, although the strongest heat flux rate decrease is simultaneous with the propagation of the oblique whistler waves.

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Simulation of the Scattering of Continuously Injected Pickup Ions outside the Heliopause

The Astrophysical Journal ◽

10.3847/1538-4357/ac2a2e ◽

2021 ◽

Vol 922 (2) ◽

pp. 271

Author(s):

Ding Sheng ◽

Kaijun Liu ◽

V. Florinski ◽

J. D. Perez

Keyword(s):

Magnetic Field ◽

Pitch Angle ◽

Injection Rate ◽

Angle Distribution ◽

Pickup Ions ◽

Isotropic Distribution ◽

Angle Scattering ◽

Background Magnetic Field ◽

First Time ◽

Continuous Injection

Abstract Hybrid simulations in 2D space and 3D velocity dimensions with continuous injection of pickup ions (PUIs) provide insight into the plasma processes that are responsible for the pitch angle scattering of PUIs outside the heliopause. The present investigation includes for the first time continuous injection of PUIs and shows how the scattering depends on the energy of the PUIs and the strength of the background magnetic field as well as the dependence on the injection rate of the time for the isotropization of the pitch angle distribution. The results demonstrate that, with the gradual injection of PUIs of a narrow ring velocity distribution perpendicular to the background magnetic field, oblique mirror mode waves develop first, followed by the growth of quasiparallel propagating ion cyclotron waves. Subsequently, the PUIs are scattered by the excited waves and gradually approach an isotropic distribution. A time for isotropization is defined to be the time at which T ∣∣/T ⊥, i.e., the ratio of the parallel to perpendicular PUI thermal energy changes from ≈0 to ≈0.15. By varying the PUI injection rate, estimates of the time for the PUI distribution to be isotropized are presented. The isotropization time obtained is shorter, ≈ months, than the time, ≈ years, required by the conventional secondary ENA mechanism to explain the IBEX ENA ribbon.

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