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Yoshiharu Omura - One of the best experts on this subject based on the ideXlab platform.
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Dynamic Variation of Earth's Outer Radiation Belt due to Nonlinear Wave-Particle Interactions
2019 URSI Asia-Pacific Radio Science Conference (AP-RASC), 2019Co-Authors: Yoshiharu OmuraAbstract:During space weather events, energetic particles are injected from the magnetotail to the inner magnetosphere, and various kinds of Wave-Particle Interactions take place. Whistler-mode chorus emissions are one of the most important waves for the dynamics of relativistic electrons forming the outer radiation belt. Chorus emissions are excited via interaction with 10 - 100 keV electrons outside the plasmasphere, and they can accelerate a fraction of resonant electrons to MeV energy. The time scale of acceleration is much shorter than that predicted by the quasi-linear theory. Effective acceleration of electrons through Landau resonance with obliquely propagating chorus emissions can also take place. Another kind of waves important for the radiation belt dynamics is EMIC rising-tone emissions excited by nonlinear interaction with energetic protons both inside and outside the plasmasphere. The EMIC emissions can interact with relativistic electrons and scatter them to lower pitch angles efficiently by nonlinear wave trapping, resulting in significant precipitation of radiation belt electrons as well as energetic protons. In these nonlinear Wave-Particle Interactions, the rising-tone frequencies of the emissions and the gradient of the magnetic field play essential roles. We review recent development of nonlinear theory and simulations that can describe dynamic nature of the radiation belts under intense space weather events.
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Nonlinear Wave-Particle Interactions in the Earth's inner magnetosphere: Dynamic variation of the Earth's outer radiation belt due to whistler-mode chorus and EMIC waves
URSI Radio Science Bulletin, 2019Co-Authors: Yoshiharu OmuraAbstract:Since publication of our previous summary paper on nonlinear Wave-Particle Interactions, published in the Radio Science Bulletin [1], we have achieved a number of advances in the study on the variation of the Earth's outer radiation belt. This paper summarizes our updated understanding of the dynamics of radiation-belt electrons (MeV) interacting with whistler-mode chorus emissions and electromagnetic ion-cyclotron (EMIC) waves, generated through nonlinear Interactions with energetic electrons and protons (10–100 keV) injected from the magnetotail at the time of magnetic disturbances. This paper is not a review paper comprehensively covering all important papers of the topics, but it is a summary of recent papers from our research group on nonlinear Wave-Particle Interactions related to the dynamics of the radiation belt. The major results are that rapid formation of the relativistic electron flux takes place through acceleration due to nonlinear wave trapping by whistler-mode rising-tone chorus emissions. A substantial amount of relativistic electron flux in the outer radiation belt is precipitated through pitch-angle scattering due to nonlinear interaction with EMIC rising-tone emissions.
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Study of Wave-Particle Interactions for whistler-mode waves at oblique angles by utilizing the gyroaveraging method†
Radio Science, 2017Co-Authors: Yikai Hsieh, Yoshiharu OmuraAbstract:We investigate the properties of whistler mode Wave-Particle Interactions at oblique wave normal angles to the background magnetic field. We find that electromagnetic energy of waves at frequencies below half the electron cyclotron frequency can flow nearly parallel to the ambient magnetic field. We thereby confirm that the gyroaveraging method, which averages the cyclotron motion to the gyrocenter and reduces the simulation from two-dimensional to one-dimensional, is valid for oblique Wave-Particle interaction. Multiple resonances appear for oblique propagation but not for parallel propagation. We calculate the possible range of resonances with the first-order resonance condition as a function of electron kinetic energy and equatorial pitch angle. To reveal the physical process and the efficiency of electron acceleration by multiple resonances, we assume a simple uniform wave model with constant amplitude and frequency in space and time. We perform test particle simulations with electrons starting at specific equatorial pitch angles and kinetic energies. The simulation results show that multiple resonances contribute to acceleration and pitch angle scattering of energetic electrons. Especially, we find that electrons with energies of a few hundred keV can be accelerated efficiently to a few MeV through the n = 0 Landau resonance.
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A computational and theoretical investigation of nonlinear wave‐particle Interactions in oblique whistlers
Journal of Geophysical Research, 2015Co-Authors: David Nunn, Yoshiharu OmuraAbstract:Most previous work on nonlinear Wave-Particle Interactions between energetic electrons and VLF waves in the Earth's magnetosphere has assumed parallel propagation, the underlying mechanism being nonlinear trapping of cyclotron resonant electrons in a parabolic magnetic field inhomogeneity. Here nonlinear Wave-Particle interaction in oblique whistlers in the Earth's magnetosphere is investigated. The study is nonself-consistent and assumes an arbitrarily chosen wave field. We employ a “continuous wave” wave field with constant frequency and amplitude, and a model for an individual VLF chorus element. We derive the equations of motion and trapping conditions in oblique whistlers. The resonant particle distribution function, resonant current, and nonlinear growth rate are computed as functions of position and time. For all resonances of order n, resonant electrons obey the trapping equation, and provided the wave amplitude is big enough for the prevailing obliquity, nonlinearity manifests itself by a “hole” or “hill” in distribution function, depending on the zero-order distribution function and on position. A key finding is that the n = 1 resonance is relatively unaffected by moderate obliquity up to 25°, but growth rates roll off rapidly at high obliquity. The n = 1 resonance saturates due to the adiabatic effect and here reaches a maximum growth at ~20 pT, 2000 km from the equator. Damping due to the n = 0 resonance is not subject to adiabatic effects and maximizes at some 8000 km from the equator at an obliquity ~55°.
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Theory and simulations of nonlinear Wave-Particle Interactions in planetary radiation belts
URSI Radio Science Bulletin, 2014Co-Authors: Yoshiharu OmuraAbstract:There has been significant progress in understanding the generation mechanism of whistler-mode chorus emissions in recent years. This is partly due to the successful reproduction of chorus emissions by computer simulations, and partly due to precise observations of the emissions by spacecraft in planetary radiation belts. We give a brief account of the nonlinear theory of the generation mechanism of chorus emissions, which has been revealed by the simulations and observations. We describe the nonlinear dynamics of resonant electrons, and the formation of the electromagnetic electron “hole” that results in resonant currents generating rising-tone emissions. In contrast, falling-tone emissions are generated through the formation of electron “hills.” We also describe the mechanism of nonlinear wave damping due to quasi-oblique propagation, which results in the formation of a gap at half the electron cyclotron frequency. The nonlinear wave-growth theory of chorus emissions can also be applied to the generation mechanism of electromagnetic ion-cyclotron-(EMIC) triggered emissions, recently found in spacecraft observations. Hybrid code simulations have confirmed that coherent rising-tone emissions are generated by energetic protons at frequencies below the proton cyclotron frequency. Electromagnetic ion-cyclotron waves can also interact with relativistic electrons. Both chorus emissions and electromagnetic ion-cyclotron-triggered emissions play important roles in controlling radiation-belt particle dynamics.
R M Thorne - One of the best experts on this subject based on the ideXlab platform.
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Radiation belt dynamics: The importance of wave‐particle Interactions
Geophysical Research Letters, 2010Co-Authors: R M ThorneAbstract:[1] The flux of energetic electrons in the Earth's outer radiation belt can vary by several orders of magnitude over time scales less than a day, in response to changes in properties of the solar wind instigated by solar activity. Variability in the radiation belts is due to an imbalance between the dominant source and loss processes, caused by a violation of one or more of the adiabatic invariants. For radiation belt electrons, non-adiabatic behavior is primarily associated with energy and momentum transfer during Interactions with various magnetospheric waves. A review is presented here of recent advances in both our understanding and global modeling of such Wave-Particle Interactions, which have led to a paradigm shift in our understanding of electron acceleration in the radiation belts; internal local acceleration, rather than radial diffusion now appears to be the dominant acceleration process during the recovery phase of magnetic storms.
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radiation belt dynamics the importance of wave particle Interactions
Geophysical Research Letters, 2010Co-Authors: R M ThorneAbstract:[1] The flux of energetic electrons in the Earth's outer radiation belt can vary by several orders of magnitude over time scales less than a day, in response to changes in properties of the solar wind instigated by solar activity. Variability in the radiation belts is due to an imbalance between the dominant source and loss processes, caused by a violation of one or more of the adiabatic invariants. For radiation belt electrons, non-adiabatic behavior is primarily associated with energy and momentum transfer during Interactions with various magnetospheric waves. A review is presented here of recent advances in both our understanding and global modeling of such Wave-Particle Interactions, which have led to a paradigm shift in our understanding of electron acceleration in the radiation belts; internal local acceleration, rather than radial diffusion now appears to be the dominant acceleration process during the recovery phase of magnetic storms.
Roderick W. Boswell - One of the best experts on this subject based on the ideXlab platform.
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Plasma ionization in low-pressure radio-frequency discharges - Part I: Optical measurements
IEEE Transactions on Plasma Science, 2008Co-Authors: Deborah O'connell, Timo Gans, Albert Meige, Peter Awakowicz, Roderick W. BoswellAbstract:The electron dynamics in the low-pressure operation regime (<5 Pa) of a neon capacitively coupled plasma is investigated using phase-resolved optical emission spectroscopy. Plasma ionization and sustainment mechanisms are governed by the expanding and contracting sheath and complex Wave-Particle Interactions. Electrons are energized through the advancing and retreating electric field of the RF sheath. The associated interaction of energetic sheath electrons with thermal bulk plasma electrons drives a two-stream instability also dissipating power in the plasma.
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Plasma Ionization in Low-Pressure Radio-Frequency Discharges—Part II: Particle-in-Cell Simulation
IEEE Transactions on Plasma Science, 2008Co-Authors: Albert Meige, Timo Gans, Deborah O'connell, Roderick W. BoswellAbstract:Plasma ionization in the low-pressure operation regime (< 5 Pa) of RF capacitively coupled plasmas (CCPs) is governed by a complex interplay of various mechanisms, such as field reversal, sheath expansion, and Wave-Particle Interactions. In a previous paper, it was shown that experimental observations in a hydrogen CCP operated at 13.56 MHz are qualitatively well described in a 1-D symmetrical particle-in-cell (PIC) simulation. In this paper, a spherical asymmetrical PIC simulation that is closer to the conditions of the highly asymmetrical experimental device is used to simulate a low-pressure neon CCP operated at 2 MHz. The results show a similar behavior, with pronounced ionization through field reversal, sheath expansion, and Wave-Particle Interactions, and can be exploited for more accurate quantitative comparisons with experimental observations.
Yuto Katoh - One of the best experts on this subject based on the ideXlab platform.
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Wave-Particle Interaction Analyzer: Direct Measurements of Wave-Particle Interactions in Planetary Magnetospheres
2020Co-Authors: Yuto Katoh, Hirotsugu KojimaAbstract:We present a new instrumentation "Wave Particle Interaction Analyzer (WPIA)" for measurement of the energy transfer process between energetic electrons and plasma waves in the magnetosphere [Fukuhara et al., 2009; Katoh et al., 2013]. The WPIA measures a relative phase angle between the wave vector and velocity vector of each particle and computes an inner product W(t), while W(t) is equivalent to the variation of the kinetic energy of energetic electrons interacting with plasma waves. The WPIA will be firstly realized by the Software-type WPIA in the ERG satellite mission to measure Interactions between energetic electrons and whistler-mode chorus in the Earth's inner magnetosphere. In this talk we discuss scientific objectives and implementation of the WPIA on board ERG.
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direct measurements of two way wave particle energy transfer in a collisionless space plasma
Science, 2018Co-Authors: Masahiro Kitahara, Yoshifumi Saito, N. Kitamura, Yuto Katoh, Yoshizumi Miyoshi, H Hasegawa, Satoko Nakamura, Masafumi Shoji, S. YokotaAbstract:Particle acceleration by plasma waves and spontaneous wave generation are fundamental energy and momentum exchange processes in collisionless plasmas. Such Wave-Particle Interactions occur ubiquitously in space. We present ultrafast measurements in Earth’s magnetosphere by the Magnetospheric Multiscale spacecraft that enabled quantitative evaluation of energy transfer in Interactions associated with electromagnetic ion cyclotron waves. The observed ion distributions are not symmetric around the magnetic field direction but are in phase with the plasma wave fields. The wave-ion phase relations demonstrate that a cyclotron resonance transferred energy from hot protons to waves, which in turn nonresonantly accelerated cold He+ to energies up to ~2 kilo–electron volts. These observations provide direct quantitative evidence for collisionless energy transfer in plasmas between distinct particle populations via Wave-Particle Interactions.
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Data processing in Software-type Wave-Particle Interaction Analyzer onboard the Arase satellite
Earth Planets and Space, 2018Co-Authors: M. Hikishima, Yuto Katoh, Yoshizumi Miyoshi, Hirotsugu Kojima, Satoshi Kasahara, Yoshiya Kasahara, T. Mitani, Nana Higashio, Ayako Matsuoka, Kazushi AsamuraAbstract:The software-type wave–particle interaction analyzer (S-WPIA) is an instrument package onboard the Arase satellite, which studies the magnetosphere. The S-WPIA represents a new method for directly observing wave–particle Interactions onboard a spacecraft in a space plasma environment. The main objective of the S-WPIA is to quantitatively detect wave–particle Interactions associated with whistler-mode chorus emissions and electrons over a wide energy range (from several keV to several MeV). The quantity of energy exchanges between waves and particles can be represented as the inner product of the wave electric-field vector and the particle velocity vector. The S-WPIA requires accurate measurement of the phase difference between wave and particle gyration. The leading edge of the S-WPIA system allows us to collect comprehensive information, including the detection time, energy, and incoming direction of individual particles and instantaneous-wave electric and magnetic fields, at a high sampling rate. All the collected particle and waveform data are stored in the onboard large-volume data storage. The S-WPIA executes calculations asynchronously using the collected electric and magnetic wave data, data acquired from multiple particle instruments, and ambient magnetic-field data. The S-WPIA has the role of handling large amounts of raw data that are dedicated to calculations of the S-WPIA. Then, the results are transferred to the ground station. This paper describes the design of the S-WPIA and its calculations in detail, as implemented onboard Arase.
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Significance of Wave-Particle Interaction Analyzer for direct measurements of nonlinear Wave-Particle Interactions
Annales Geophysicae, 2013Co-Authors: Yuto Katoh, Yoshizumi Miyoshi, M. Kitahara, Hirotsugu Kojima, Yoshiharu Omura, Satoshi Kasahara, Masafumi Hirahara, Kanako Seki, Kazushi Asamura, Takeshi TakashimaAbstract:Abstract. In the upcoming JAXA/ERG satellite mission, Wave Particle Interaction Analyzer (WPIA) will be installed as an onboard software function. We study the statistical significance of the WPIA for measurement of the energy transfer process between energetic electrons and whistler-mode chorus emissions in the Earth's inner magnetosphere. The WPIA measures a relative phase angle between the wave vector E and velocity vector v of each electron and computes their inner product W, where W is the time variation of the kinetic energy of energetic electrons interacting with plasma waves. We evaluate the feasibility by applying the WPIA analysis to the simulation results of whistler-mode chorus generation. We compute W using both a wave electric field vector observed at a fixed point in the simulation system and a velocity vector of each energetic electron passing through this point. By summing up Wi of an individual particle i to give Wint, we obtain significant values of Wint as expected from the evolution of chorus emissions in the simulation result. We can discuss the efficiency of the energy exchange through Wave-Particle Interactions by selecting the range of the kinetic energy and pitch angle of the electrons used in the computation of Wint. The statistical significance of the obtained Wint is evaluated by calculating the standard deviation σW of Wint. In the results of the analysis, positive or negative Wint is obtained at the different regions of velocity phase space, while at the specific regions the obtained Wint values are significantly greater than σW, indicating efficient Wave-Particle Interactions. The present study demonstrates the feasibility of using the WPIA, which will be on board the upcoming ERG satellite, for direct measurement of Wave-Particle Interactions.
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A new instrument for the study of Wave-Particle Interactions in space: One-chip Wave-Particle Interaction Analyzer
Earth Planets and Space, 2009Co-Authors: H. Fukuhara, Yuto Katoh, Hirotsugu Kojima, Yoshiharu Omura, Yoshikatsu Ueda, Hiroshi YamakawaAbstract:Wave-Particle Interactions in a collisionless plasma have been analyzed in several past space science missions but direct and quantitative measurement of the Interactions has not been conducted. We here introduce the Wave-Particle Interaction Analyzer (WPIA) to observe Wave-Particle Interactions directly by calculating the inner product between the electric field of plasma waves and of plasma particles. The WPIA has four fundamental functions: waveform calibration, coordinate transformation, time correction, and interaction calculation. We demonstrate the feasibility of One-chip WPIA (O-WPIA) using a Field Programmable Gate Array (FPGA) as a test model for future science missions. The O-WPIA is capable of real-time processing with low power consumption. We validate the performance of the O-WPIA including determination of errors in the calibration and power consumption.
H Reme - One of the best experts on this subject based on the ideXlab platform.
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a three dimensional plasma and energetic particle investigation for the wind spacecraft
Space Science Reviews, 1995Co-Authors: K A Anderson, M Mccarthy, S Ashford, C W Carlson, D W Curtis, R E Ergun, D E Larson, J P Mcfadden, G K Parks, H RemeAbstract:This instrument is designed to make measurements of the full three-dimensional distribution of suprathermal electrons and ions from solar wind plasma to low energy cosmic rays, with high sensitivity, wide dynamic range, good energy and angular resolution, and high time resolution. The primary scientific goals are to explore the suprathermal particle population between the solar wind and low energy cosmic rays, to study particle accleration and transport and Wave-Particle Interactions, and to monitor particle input to and output from the Earth's magnetosphere.
