Session JO05: Space Plasmas

Solar Charge-Electric Fields and Jets in Quantitative Agreement with Ulysses and PSP Satellites

A new “charge-electric” model of energization of the Solar Wind and Corona is described, including electro-magnetic particle effects precluded in the no-charge-fluid approximation.  The parameter-free model gives quantitative agreement with the maximum proton energies measured by Ulysses (McComas 2000); and with the electric potential versus radius obtained from PSP electron VDF data (Berčič 2021, Halekas 2022).  The model builds on standard solar models for particle density and temperature, by adding two plasma effects.  First, static force-balance equilibrium of protons and electrons requires a static electric field 1/2 as strong as gravity on each proton (Pannekoek 1924).  Second, the steady flow of fusion energy drags additional electrons out from the plasma recombination sheath, here limited by a global "virial" relation between gravity and electric potentials.  This uniquely determines the total charge state of +460.C, with a surface potential of +6.keV compared to a gravity well of 2.keV for protons, explaining the energetics of Ulysses and PSP.  Dynamically, the protons accelerate as pinched "Lightning Jets" through the neutral Atmosphere, appearing as the ubiquitous Spicules, and "heating" the (non-LTE) Corona, each with 10⁹ Amps of +/- current generating fluctuating magnetic fields.  The DC radial electric field can also "neutrally levitate" a 1/3-ionized gas cloud, glowing as a Prominence or Arc due to internal lateral currents driven by surface potential variations.

    

Particle-In-Cell Simulations --- Ion Beam Instabilities and The Generation of Alfven and Whistler Waves in Low β Plasma

Ion beam-driven instabilities in a  collisionless space plasma with  low β, i.e, low plasma and magnetic pressure ratio, are investigated using Particle-in-Cell (PIC) simulations. Specifically, the effects of different ion drift velocities on the development of Buneman and resonant electromagnetic (EM) right-handed (RH) ion beam instabilities are studied. Our simulations reveal that both instabilities can be driven when the ion beam drift exceeds the theoretical thresholds. The Buneman instability, which is weakly triggered initially,  dissipates only a small fraction of the kinetic energy of the ion beam while causing significant electron heating, owing to the small electron-ion mass ratio. However, we find that the ion beam-driven Buneman instability is quenched effectively by the resonant EM RH ion beam instability.  Instead, the resonant EM RH ion beam instability dominates when the ion drift velocity is larger than the Alfven speed, leading to the generation of RH Alfven waves and RH whistler waves. We find that the intensity of Alfven waves decreases with decrease of ion beam drift velocity, while the intensity of whistler waves increases. Our results provide new insights into the complex interplay between ion beams and plasma instabilities in low β collisionless space plasmas.   

Excitation of Alfven Wave Parametric Decay in 3D Open-Boundary Low-Beta Plasma

We present the first 3D, open-boundary, hybrid kinetic-fluid simulations of Alfven wave parametric decay instability (PDI) in a low-beta plasma. The Alfven wave PDI—where a large forward pump Alfven wave decays into a backward child Alfven wave and a forward ion acoustic wave—is a significant process for understanding wave dissipation and plasma heating. However, details regarding how PDI is excited in realistic 3D open systems and how the finite perpendicular wave scale—as found in both laboratory and space plasmas—affects the excitation remain elusive. Our 3D simulations and theoretical analysis reveal that PDI excitation is strongly influenced by the wave damping present, including electron-ion collisional damping (represented by constant resistivity) and geometrical attenuation associated with the finite-scale Alfven wave, and ion Landau damping of the child acoustic wave. The perpendicular wave scale alone, however, plays no discernible role: waves of different perpendicular scales exhibit similar instability excitation as long as the magnitude of the parallel ponderomotive force remains unchanged. This new understanding of 3D Alfven wave PDI physics is essential for advancing laboratory studies of the fundamental plasma process and may provide insights into the role of PDI in low-beta space plasmas.   

Spatially Resolved Spectral Measurements of EIH Waves Generated by Plasma Shear Flow Layer

Waves and instabilities generated by flows in plasmas due to the presence of mutually perpendicular electric and magnetic fields are of general relevance to the study of multiscale plasma dynamics and space physics. In particular, the waves generated by the shear in such flow profiles can have both stabilizing and destabilizing effects on the plasma depending on the shear's magnitude and scale length and may be the trigger of energy cascades. Over the years, laboratory experiments have been performed to simulate the broadband emissions from dipolarization fronts (highly compressed, Earth-ward propagating plasma sheets resulting from reconnection events) that energize the near-earth plasma environment, resulting in magnetospheric substorms. In this experiment, spatially scanned 3-axis Bdot and floating potential probes are used to conduct temporal cross-correlation measurements of fluctuations generated by the shear at the boundary of a cylindrical flow layer in a magnetized plasma column. This 3-dimensional data set is decomposed into cylindrical harmonics and analyzed using discrete Fourier transforms to isolate the 2-dimensional spatial structure of each mode and to reconstruct the dispersion relation of the excited waves. Since the shear layer length scale is sub-Larmor radius and the plasma skin depth to wavelength ratio transitions from less than to greater than unity, these results are compared to the non-local electrostatic and electromagnetic theory for Electron-Ion Hybrid (EIH) waves. It is shown that, in accordance with theory, the modes excited are broadly distributed around m=3 and that the waves primarily propagate in the direction of the cross-field flow.   

Electron velocity distribution functions in the solar wind

We discuss observations of 38,229 electron velocity distribution functions (VDFs) in the solar wind observed by the Wind spacecraft near 1 AU.  The data are take from two time periods: January 1–23, 2013 and July 1–31, 2017.  This represents a proof of concept study to illustrate the calibration of the 3DP instrument under a wide range of solar wind conditions.  Examination of the properties of the entire VDF in addition to the core, halo, and strahl populations will be presented.  Emphasis will be placed on deviations from isotropic Maxwellian VDFs and the importance of the kinetic features in each subcomponent of the distributions.   

Mechanisms for electron trapping and acceleration in magnetic islands from lab to space

Understanding how magnetic islands (toroidally reconnected magnetic flux tubes) trap and accelerate electrons can improve models for space weather forecasting and disruption mitigation strategies in fusion devices. Recent experiments at the DIII-D tokamak demonstrated that electrons of energies up to 20MeV can be trapped in magnetic islands located in the core plasma. As 20MeV-electrons travel at relativistic velocities (~99.967% of the speed of light), it can be expected that the resulting particle drifts are large enough to prevent the electrons from following smaller features in the magnetic field topology, such as islands. Here we propose that suprathermal, but nonrelativistic, electrons are initially trapped in islands and subsequently accelerated to relativistic speeds through a Fermi-type process. The electrons must be already suprathermal and close-to-collisionless for efficient Fermi acceleration. We calculate the characteristic island width needed to confine suprathermal electrons and the characteristic trapping time needed for acceleration to the electron energies measured in the DIII-D experiments.   

Nonlinear Wave-Particle Interactions in the Formation of Chorus Wave Subpackets: 2-D Particle-in-Cell Simulation

We investigate nonlinear wave-particle interactions during the formation of chorus wave subpackets using a 2-D GCPIC simulation in dipole fields. The rising-tone chorus waves are self-consistently excited by energetic electrons near the magnetic equator, and the waves consist of a series of subpackets and become oblique during their propagation. We investigate electron distributions in various phase spaces associated with subpacket formation. It is found that electron holes in the wave phase space, formed due to nonlinear cyclotron resonance, oscillate in size over time during subpacket formation. The associated inhomogeneity factor varies accordingly, leading to different frequency chirping in various phases of the subpackets. Moreover, Landau resonance is found to coexist with cyclotron resonance. This study provides a comprehensive analysis of multidimensional electron distributions involved in subpacket formation, enhancing our understanding of the nonlinear physics in chorus wave evolution.   

Resonant Electron Signatures in the Formation of Chorus Wave Subpackets

A 2-D GCPIC simulation in a dipole field system has been conducted to explore the excitation of oblique whistler mode chorus waves driven by energetic electrons with temperature anisotropy. The rising tone chorus waves are initially generated near the magnetic equator, consisting of a series of subpackets, and become oblique during their propagation. It is found that electron holes in the wave phase space, which are formed due to the nonlinear cyclotron resonance, oscillate in size with time during subpacket formation. The associated inhomogeneity factor varies accordingly, giving rise to various frequency chirping in different phases of subpackets. Distinct nongyrotropic electron distributions are detected in both wave gyrophase and stationary gyrophase. Landau resonance is found to coexist with cyclotron resonance. This study provides multidimensional electron distributions involved in subpacket formation, enabling us to comprehensively understand the nonlinear physics in chorus wave evolution.   

Observations of electron energization in moderate guide field magnetic reconnection using MMS data

Magnetic reconnection has been observed by spacecraft under differing conditions, including varying guide field strengths and asymmetric upstream conditions. While spacecraft observations of the ion and electron diffusion regions and the J.E energization of the particles have been used to identify magnetic reconnection, the details of how the electron velocity distribution responds to the reconnection electric field, resulting in either electron heating or acceleration, remain poorly understood. Here we observe the response of the electrons as a function of velocity space to the parallel electric field in moderate guide field reconnection, resulting in electron energization. Applying the novel field-particle correlation technique to MMS measurements of the electric field and the electron velocity distribution in the Earth's magnetosheath, we obtain the velocity-space signature of the electron energization. We explore the variation of the velocity-space signature of electron energization as the spacecraft traverses the exhaust region, illuminating the electron response to the parallel electric field in different regions of the reconnection geometry.   

A nonlinear free-electron laser model of whistler-mode chorus amplification in the magnetosphere

We extend the free-electron laser (FEL) model of whistler chorus amplification in the magnetosphere to the nonlinear regime. Under typical conditions the model predicts a seed wave will initially grow exponentially, in agreement with the linear model. However, whereas the linear model predicts exponential growth for all times, the nonlinear model predicts mode saturation followed by quasiperiodic amplitude pulses. It has been shown that a nonlinear free-electron laser (NLFEL) can be modeled by the Ginzburg-Landau equation (GLE) whose coefficients can be derived via a WKB approximation of the NLFEL equations. We explore the consequences of the GLE for whistler-mode chorus, including the potential formation of solitary wave solutions, which are known solutions of the GLE (these solutions are not solitons because the GLE fails the Painleve test). In the spatially homogeneous limit, the GLE reduces to the Stuart-Landau equation (SLE). We find that the SLE reproduces the exponential growth phase and the saturation amplitude predicted by the NLFEL equations, furthering the connection between the NLFEL equations and the GLE. We will compare analytical and numerical solutions with in situ satellite observations.   

Use of VLF Plasma Waves in the Ionosphere for Detection and Tracking of Harmful Space Debris Produced by the 26 June 2024 Breakup of RESURS P1

The number of satellites launched into low Earth orbit (LEO) is increasing at an exponential rate.  Launches support deployment of multi-satellite constellations for many applications.  Experiments with electric field sensors on Swarm-E have been conducted to better locate the positions of satellites and space debris for prevention of collisions.  Currently, there are about 27,000 known space objects and over 100 million of unknown pieces of space debris.  Collision avoidance requires precise knowledge of the positions for all space objects.   New techniques are being developed to detect the small, < 10 cm, objects by the plasma waves they generate in space.  The bases for this technique is that all space objects in orbit around the Earth (1) pass through a magnetized plasma, (2) become electrically charged, and thus (3) produce detectable plasma waves.  Field aligned irregularities (FAIs) in the path of orbiting space objects are monitored by the SuperDARN radar backscatter and by in situ electron density probes.  Space debris and satellites moving through these irregularities and can excite plasma emissions such as whistler, compressional Alfven, or lower hybrid waves.  Orbital kinetic energy is the source of lower hybrid waves which is converted into an EM plasma oscillation when a charged space object encounters a field aligned irregularity (FAI).  Such whistlers and magnetosonic waves propagate undamped the source regions and can be detected at >100 km range.  This technique is being used to search for the orbits of pieces of the Russian RESURS P1 (NORAD 39186) that broke up on 26 June 2024.    

Connecting Kinetic and MHD Scales in Flows of Partially Ionized Plasma with Shocks

Flows of partially ionized plasma are frequently characterized by the presence of both thermal and nonthermal populations of ions. Such flows cannot be modeled using traditional MHD equations and require more advanced approaches to treat them. If a non-thermal component of ions is formed due to charge exchange and collisions between the thermal ions and neutral atoms, it experiences the action of magnetic field, its distribution function is isotropized, and it soon acquires the velocity of the ambient plasma without being thermodynamically equilibrated. This situation, occurs in the outer heliosphere -- the part of interstellar space beyond the solar system whose properties are determined by the solar wind interaction with the local interstellar medium. To describe such flows we have developed a numerical model that describes the flow of plasma with MHD equations, whereas the transport of neutral atoms is modeled kinetically, by solving the corresponding Boltzmann equations. The presence of non-termal (pickup) ions (PUIs) and turbulence they generate requires their kinetic treatment at collisionless shocks. We incorporate such kinetic process intothe global MHD model of the heliosphere by imposing specifcally designed boundariy conditions at the heliospheric termination shock. We describe the model details and comapre simulation results with the IBEX, New Horizons, and Voyager data.   

Nonlinear evolution and propagation of KdV solitons using fully kinetic PIC simulations

In this study, we conduct a comprehensive investigation into the behavior of ion acoustic solitary waves (solitons) of varying amplitude launched into a one-dimensional plasma in the laboratory frame utilizing fully kinetic particle-in-cell (PIC) simulations. The initial conditions for the ion density, velocity, and potential are prescribed according to the solution of the Korteweg-de Vries (KdV) equation, while the electron density is initialized based on the solution of Poisson's equation at the initial time step, treating ions as a cold species and assigning a temperature to the electrons. Our findings reveal that small amplitude solitons maintain their initial KdV state with negligible particle trapping, whereas larger amplitude solitons exhibit nonlinear evolution to a saturated state at a higher amplitude that deviates from the KdV soliton, with nonlinear effects arising from particle trapping. In particular, we find that the soliton amplitude oscillates roughly at the electron bounce frequency. The soliton ion density, potential, and velocity are found to exhibit better agreement with a modified KdV equation, which incorporates a nonlinear term to capture trapping phenomena or a nonlinear term due to higher order dispersive effects. Furthermore, our results demonstrate that the relationship between soliton speed and amplitude is inconsistent with existing theoretical predictions.