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Sökning: WFRF:(Vasko I. Y.)

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1.
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2.
  • Lotekar, A., et al. (författare)
  • Multisatellite MMS Analysis of Electron Holes in the Earth's Magnetotail : Origin, Properties, Velocity Gap, and Transverse Instability
  • 2020
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:9
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a statistical analysis of more than 2,400 electrostatic solitary waves interpreted as electron holes (EH) measured aboard at least three Magnetospheric Multiscale (MMS) spacecraft in the Earth's magnetotail. The velocities of EHs are estimated using the multispacecraft interferometry. The EH velocities in the plasma rest frame are in the range from just a few km/s, which is much smaller than ion thermal velocity V-Ti, up to 20,000 km/s, which is comparable to electron thermal velocity V-Te. We argue that fast EHs with velocities larger than about 0.1V(Te) are produced by bump-on-tail instabilities, while slow EHs with velocities below about 0.05V(Te) can be produced by warm bistream and, probably, Buneman-type instabilities. We show that typically fast and slow EHs do not coexist, indicating that the instabilities producing EHs of different types operate independently. We have identified a gap in the distribution of EH velocities between V-Ti and 2V(Ti), which is considered to be the evidence for self-acceleration (Zhou & Hutchinson, 2018) or ion Landau damping of EHs. Parallel spatial scales and amplitudes of EHs are typically between lambda(D) and 10 lambda(D) and between 10(-3) T-e and 0.1 T-e, respectively. We show that electrostatic potential amplitudes of EHs are below the threshold of the transverse instability and highly likely restricted by the nonlinear saturation criterion of electron streaming instabilities seeding electron hole formation: e Phi(0)less than or similar to me pi(2)d(parallel to)(2), where pi = min(gamma, 1.5 omega(ce)), where gamma is the increment of instabilities seeding EH formation, while pi(ce) is electron cyclotron frequency. The implications of the presented results are discussed.
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3.
  • Tong, Y., et al. (författare)
  • Simultaneous Multispacecraft Probing of Electron Phase Space Holes
  • 2018
  • Ingår i: Geophysical Research Letters. - : Blackwell Publishing Ltd. - 0094-8276 .- 1944-8007. ; 45:21, s. 11,513-11,519
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a series of electron holes observed simultaneously on four Magnetospheric Multiscale spacecraft in the plasma sheet boundary layer. The multispacecraft probing shows that the electron holes propagated quasi-parallel to the local magnetic field with velocities of a few thousand kilometers per second with parallel spatial scales of a few kilometers (a few Debye lengths). The simultaneous multispacecraft probing allows analyzing the 3-D configuration of the electron holes. We estimate the electric field gradients and charge densities associated with the electrons holes. The electric fields are fit to simple 3-D electron hole models to estimate their perpendicular scales and demonstrate that the electron holes were generally not axially symmetric with respect to the local magnetic field. We emphasize that most of the electron holes had a complicated structure not reproduced by the simple models widely used in single-spacecraft studies.
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4.
  • Wang, R., et al. (författare)
  • Electrostatic Solitary Waves in the Earth's Bow Shock : Nature, Properties, Lifetimes, and Origin
  • 2021
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:7
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a statistical analysis of >2,100 bipolar electrostatic solitary waves (ESWs) collected from 10 quasi-perpendicular Earth's bow shock crossings by Magnetospheric Multiscale spacecraft. We developed and implemented a correction procedure for reconstruction of actual electric fields, velocities, and other properties of ESW, whose spatial scales are typically comparable with or smaller than spatial distance between voltage-sensitive probes. We found that more than 95% of the ESW are of negative polarity with amplitudes typically below a few Volts and 0.1T(e) (5-30 V or 0.1-0.3T(e) for a few percent of ESW), spatial scales of 10-100 m or lambda(D)-10 lambda(D), and velocities from a few tens to a few hundred km/s that is on the order of local ion-acoustic speed. The spatial scales of ESW are correlated with local Debye length lambda(D). The ESW have electric fields generally oblique to magnetic field and they propagate highly oblique to shock normal N; more than 80% of ESW propagate within 30 degrees of the shock plane LM. In the shock plane, ESW typically propagates within a few tens of degrees of local magnetic field projection B-LM and preferentially opposite to N x B-LM. We argue that the ESW of negative polarity are ion holes produced by ion-ion streaming instabilities. We estimate ion hole lifetimes to be 10-100 ms, or 1-10 km in terms of traveling distance. The revealed statistical properties will be useful for quantitative studies of electron thermalization in the Earth's bow shock.
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5.
  • Hanson, E. L. M., et al. (författare)
  • Shock Drift Acceleration of Ions in an Interplanetary Shock Observed by MMS
  • 2020
  • Ingår i: Astrophysical Journal Letters. - : IOP PUBLISHING LTD. - 2041-8205 .- 2041-8213. ; 891:1
  • Tidskriftsartikel (refereegranskat)abstract
    • An interplanetary (IP) shock wave was recorded crossing the Magnetospheric Multiscale constellation on 2018 January 8. Plasma measurements upstream of the shock indicate efficient proton acceleration in the IP shock ramp: 2-7 keV protons are observed upstream for about three minutes (similar to 8000 km) ahead of the IP shock ramp, outrunning the upstream waves. The differential energy flux of 2-7 keV protons decays slowly with distance from the ramp toward the upstream region (dropping by about half within 8 Earth radii from the ramp) and is lessened by a factor of about four in the downstream compared to the ramp (within a distance comparable to the gyroradius of similar to keV protons). Comparison with test-particle simulations has confirmed that the mechanism accelerating the solar wind protons and injecting them upstream is classical Shock Drift Acceleration (SDA). This example of observed proton acceleration by a low-Mach, quasi-perpendicular shock may be applicable to astrophysical contexts, such as supernova remnants or the acceleration of cosmic rays.
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6.
  • Lotekar, Ajay, et al. (författare)
  • Kinetic-scale Current Sheets in Near-Sun Solar Wind : Properties, Scale-dependent Features and Reconnection Onset
  • 2022
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 929:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We present statistical analysis of 11,200 proton kinetic-scale current sheets (CS) observed by the Parker Solar Probe during 10 days around the first perihelion. The CS thickness lambda is in the range from a few to 200 km with the typical value around 30 km, while current densities are in the range from 0.1 to 10 mu A m(-2) with the typical value around 0.7 mu A m(-2). These CSs are resolved thanks to magnetic field measurements at 73-290 samples s(-1) resolution. In terms of proton inertial length lambda(p), the CS thickness lambda is in the range from about 0.1 to 10 lambda(p) with the typical value around 2 lambda(p). The magnetic field magnitude does not substantially vary across the CSs, and accordingly the current density is dominated by the magnetic-field-aligned component. The CSs are typically asymmetric with statistically different magnetic field magnitudes at the CS boundaries. The current density is larger for smaller-scale CSs, J(0) approximate to 0.15 x (lambda/100 km)(-0.76) mu A m(-2), but does not statistically exceed the Alfven current density J(A) corresponding to the ion-electron drift of the local Alfven speed. The CSs exhibit remarkable scale-dependent current density and magnetic shear angles, J(0)/J(A) approximate to 0.17 x (lambda/lambda(p))(-0.67) and Delta theta approximate to 21 degrees x (lambda/lambda(p))(0.32). Based on these observations and comparison to recent studies at 1 au, we conclude that proton kinetic-scale CSs in the near-Sun solar wind are produced by turbulence cascade, and they are automatically in the parameter range, where reconnection is not suppressed by the diamagnetic mechanism, due to their geometry dictated by turbulence cascade.
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7.
  • Vasko, I. Y., et al. (författare)
  • Solitary Waves Across Supercritical Quasi-Perpendicular Shocks
  • 2018
  • Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:12, s. 5809-5817
  • Tidskriftsartikel (refereegranskat)abstract
    • We consider intense electrostatic solitary waves (ESW) observed in a supercritical quasi-perpendicular Earth's bow shock crossing by the Magnetospheric Multiscale Mission. The ESW have spatial scales of a few tens of meters (a few Debye lengths) and propagate oblique to a local quasi-static magnetic field with velocities from a few tens to a few hundred kilometers per second in the spacecraft frame. Because the ESW spatial scales are comparable to the separation between voltage-sensitive probes, correction factors are used to compute the ESW electric fields. The ESW have electric fields with amplitudes exceeding 600mV/m (oriented oblique to the local magnetic field) and negative electrostatic potentials with amplitudes of a few tenths of the electron temperature. The negative electrostatic potentials indicate that the ESW are not electron phase space holes, while interpretation in terms of ions phase space holes is also questionable. Whatever is their nature, we show that due to the oblique electric field orientation the ESW are capable of efficient pitch-angle scattering and isotropization of thermal electrons. Due to the negative electrostatic potentials the ESW Fermi reflects a significant fraction of the thermal electrons streaming from upstream (downstream) back to upstream (downstream) region, thereby affecting the shock dynamics. The role of the ESW in electron heating is discussed. Plain Language Summary Processes governing electron thermalization across shock waves are not entirely understood. The high resolution particle and 3-D electric field measurements provided by the Magnetospheric Multiscale Mission make it possible to study the Earth's bow shock that is an excellent laboratory for addressing the electron thermalization across supercritical shock waves. Previous observations showed that electron heating across the bow shock is generally governed by macroscopic cross-shock electrostatic field. On the other hand, the role of the turbulence observed across the bow shock in the electron thermalization has remained unclear. In this letter we consider a particular bow shock crossing by the Magnetospheric Multiscale Mission and focus on the role of the high amplitude electrostatic solitary waves in the electron thermalization process. We accurately estimate the electrostatic solitary wave parameters and show that due to electric fields oriented oblique to a local DC magnetic field and negative electrostatic potentials with amplitudes of a few tenths of the electron temperature, these Debye-scale structures are capable of efficient pitch angle scattering, Fermi reflection, and isotropization of thermal electrons.
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8.
  • Wang, R., et al. (författare)
  • Electrostatic Turbulence and Debye-scale Structures in Collisionless Shocks
  • 2020
  • Ingår i: Astrophysical Journal Letters. - : IOP PUBLISHING LTD. - 2041-8205 .- 2041-8213. ; 889:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We present analysis of more than 100 large-amplitude bipolar electrostatic structures in a quasi-perpendicular supercritical Earth's bow shock crossing, measured by the Magnetospheric Multiscale spacecraft. The occurrence of the bipolar structures is shown to be tightly correlated with magnetic field gradients in the shock transition region. The bipolar structures have negative electrostatic potentials and spatial scales of a few Debye lengths. The bipolar structures propagate highly oblique to the shock normal with velocities (in the plasma rest frame) of the order of the ion-acoustic velocity. We argue that the bipolar structures are ion phase space holes produced by the two-stream instability between incoming and reflected ions. This is the first identification of the ion two-stream instability in collisionless shocks.
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9.
  • Wang, R., et al. (författare)
  • Multisatellite Observations of Ion Holes in the Earth's Plasma Sheet
  • 2022
  • Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:8
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the first observations of electrostatic solitary waves with electrostatic potential of negative polarity around a fast plasma flow in the Earth's plasma sheet. The solitary waves are observed aboard four Magnetospheric Multiscale spacecraft, which allowed accurately estimating solitary wave properties. Based on a data set of 153 solitary waves, we show that they are locally one-dimensional Debye-scale structures with amplitudes up to 20% of local electron temperature and they propagate at plasma frame speeds ranging from a tenth to a few ion-acoustic speeds at arbitrary angles to the local magnetic field. The solitary waves are associated with multi-component proton distributions and their velocities are around those of a beam-like proton population. We argue that the solitary waves are ion holes, nonlinear structures produced by ion-streaming instabilities, and conclude that once ions are not magnetized, ion holes can propagate oblique to local magnetic field.
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