237 research outputs found
Spectral characteristics of waves and particles in the model of cyclotron wave-particle interactions near plasmapause
International audienceFurther analysis of energetic electron precipitation at the evening sector of magnetosphere is performed. In the framework of the quantitative model of cyclotron wave-particle interactions developed in the previous Pasmanik et al. paper, the case of finite spread over energies of initial energetic electron distribution is studied. The solution for distribution function of energetic electron is found. The energetic spectrum of trapped and precipitating electrons and whistler wave spectrum are analysed
Electromagnetic cyclotron instabilities in bi-Kappa distributed plasmas : a quasilinear approach
Anisotropic bi-Kappa distributed plasmas, as encountered in the solar wind and planetary magnetospheres,are susceptible to a variety of kinetic instabilities including the cyclotron instabilities driven by an excess ofperpendicular temperature Tâ„ > Tâ„ (where â„, â„ denote directions relative to the mean magnetic field). Theseinstabilities have been extensively investigated in the past, mainly limiting to a linear stability analysis. Abouttheir quasilinear (weakly nonlinear) development some insights have been revealed by numerical simulationsusing PIC and Vlasov solvers. This paper presents a self-consistent analytical approach, which provides forboth the electron and proton cyclotron instabilities an extended picture of the quasilinear time evolution ofthe anisotropic temperatures as well as the wave energy densities
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High-Speed Data Acquisition System for Nanoscale Imaging
This technical report is the product of a senior design project in the Department of Electrical and
Computer Engineering at the University of Texas at Austin and was written in conformance with
the ECE senior design final report requirements. Current scanning probe microscopy systems are
often limited by the speed and resultion at which they sample. In this technical report, we
demonstrate a novel data acquisition, processing, and visualization system that leverages
machine learning to collect and analyze data from an extant scanning probe microscope at 4
MS/s. The system comprises four subsystems: a current preamplifier, a data acquisition system, a
data processing and visualization module, and an interactive graphic user interface. The current
preamplifier amplifies small currents on the order of nanoamps to voltages readable by the data
acquisition system. The data acquisition system takes in input data from the scanning probe
microscope and stores them into usable file formats for the data processing module. The data
processing module uses various software signal processing techniques to analyze and visualize
the data. Finally, the graphic user interface acts as the main user control system, initiating data
collection and viewing collected data on user command. Future work on this system includes
system-wide testing as well as optimizing the robustness of each subsystem to meet the
constraints of the scanning probe microscope system.Electrical and Computer Engineerin
Nonlinear local parallel acceleration of electrons through Landau trapping by oblique whistler mode waves in the outer radiation belt
International audienceSimultaneous observations of electron velocity distributions and chorus waves by the Van Allen Probe B are analyzed to identify long-lasting (more than 6 h) signatures of electron Landau resonant interactions with oblique chorus waves in the outer radiation belt. Such Landau resonant interactions result in the trapping of Ë1-10 keV electrons and their acceleration up to 100-300 keV. This kind of process becomes important for oblique whistler mode waves having a significant electric field component along the background magnetic field. In the inhomogeneous geomagnetic field, such resonant interactions then lead to the formation of a plateau in the parallel (with respect to the geomagnetic field) velocity distribution due to trapping of electrons into the wave effective potential. We demonstrate that the electron energy corresponding to the observed plateau remains in very good agreement with the energy required for Landau resonant interaction with the simultaneously measured oblique chorus waves over 6 h and a wide range of L shells (from 4 to 6) in the outer belt. The efficient parallel acceleration modifies electron pitch angle distributions at energies Ë50-200 keV, allowing us to distinguish the energized population. The observed energy range and the density of accelerated electrons are in reasonable agreement with test particle numerical simulations
Frequencies of wave packets of whistler-mode chorus inside its source region: a case study
Whistler-mode chorus is a structured wave emission observed in the Earth's magnetosphere in a frequency range from a few hundreds of Hz to several kHz. We investigate wave packets of chorus using high-resolution measurements recorded by the WBD instrument on board the four Cluster spacecraft. A night-side chorus event observed during geomagnetically disturbed conditions is analyzed. We identify lower and upper frequencies for a large number of individual chorus wave packets inside the chorus source region. We investigate how these observations are related to the central position of the chorus source which has been previously estimated from the Poynting flux measurements. We observe typical frequency bandwidths of chorus of approximately 10% of the local electron cyclotron frequency. Observed time scales are around 0.1 s for the individual wave packets. Our results indicate a lower occurrence probability for lower frequencies in the vicinity of the central position of the source compared to measurements recorded closer to the outer boundaries of the source. This is in agreement with recent research based on the backward wave oscillator theory
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