Power Spectrum in the Conductive Terrestrial Ionosphere

Stochastic differential equation of the phase fluctuations is derived for the collision conductive magnetized plasma in the polar ionosphere applying the complex geometrical optics approximation. Calculating second order statistical moments it was shown that the contribution of the longitudinal conductivity substantially exceeds both Pedersen and Hall’s conductivities. Experimentally observing the broadening of the spatial power spectrum of scattered electromagnetic waves which equivalent to the brightness is analyzed for the elongated ionospheric irregularities. It was shown that the broadening of the spectrum and shift of its maximum in the plane of the location of an external magnetic field (main plane) less than in perpendicular plane for plasmonic structures having linear scale tenth of kilometer; and substantially depends on the penetration angle of an incident wave in the conductive collision turbulent magnetized ionospheric plasma. The angle-of-arrival (AOA) in the main plane has the asymmetric Gaussian form while in the perpendicular plane increases at small anisotropy factors and then tends to the saturation for the power-low spectrum characterizing electron density fluctuations. Longitudinal conductivity fluctuations increase the AOAs of scattered radiation than in magnetized plasma with permittivity fluctuations. Broadening of the temporal spectrum containing the drift velocity of elongated ionospheric irregularities in the polar ionosphere allows to solve the reverse problem restoring experimentally measured velocity of the plasma streams and characteristic linear scales of anisotropic irregularities in the terrestrial ionosphere

Particle-in-cell simulation of astrophysical plasmas: probing the origin of cosmic rays

Cosmic rays, the product of natural extraterrestrial particle accelerators far more powerful than the LHC, were first detected a century ago. A standard model of cosmic-ray acceleration in supernova remnants has begun to emerge, but a number of questions still require satisfactory answers. The maximum particle energy attainable via the most favored mechanism, diffusive shock acceleration, is limited by the amplitude of magnetic-field turbulence in the unshocked interstellar or circumstellar medium, but cosmic rays are observed at high enough energies that some magnetic-field amplification is required. By what mechanisms might this amplification occur, and can it operate to a great enough extent to account for those cosmic rays thought to be of Galactic origin? A number of proposed solutions involve instabilities arising from interactions between cosmic rays and the upstream plasma, whose evolution becomes highly nonlinear. A related question explored is whether the presence of accelerated particles in the shock vicinity has any microscopic effect on the instabilities governing the shock itself. Particle-in-cell kinetic simulations allow us to investigate the growth and saturation of these instabilities at the (astrophysically) microscopic scale, providing valuable insights and important considerations for self-consistent macroscopic models of particle acceleration

On the Origin of Close-Range E Region Echoes Observed by SuperDARN HF Radars in the Mid- and High Latitudes

The Super Dual Auroral Radar Network (SuperDARN) is a global network of coherent high frequency (HF) radars located in the polar, high- and mid-latitudes of both the Northern and Southern hemispheres. This thesis deals with close-range SuperDARN echoes (oblique HF backscatter from the lower part of the ionosphere). The aim of this thesis is to shed light on the origin of these echoes. Previous studies have been content to propose explanations for the origin of these echoes without thorough checking of the proposed mechanisms against constraints available from various radars and other important information. For the purpose of clarifying the situation, a chain of SuperDARN radars in the Northern and Southern hemispheres and several years of daily statistics have been used. This has allowed for several findings. Notably, the close-range SuperDARN echoes show diurnal and seasonal variations and their properties with respect to signal-to-noise-ratio, Doppler velocity and Doppler width vary. Three distinct populations of close-range HF backscatter have been established: (1) a morning population (0400-0700 LT), (2) a midday summer population (0800-1300 LT) and (3) a pre-midnight (2100-2300 LT) population. The morning population is associated with meteor trails which are observed to be peaking near local dawn as expected, and already suggested by previous research. High latitude SuperDARN radars also had echoes (pre-midnight population) with higher Doppler velocities than the others yet the Doppler velocities are smaller than that expected from auroral E region echoes. Given the time and location of this population of echoes, it has been concluded that they are a special class of high latitude E region echoes at high aspect angle which have been termed ``high aspect irregularity region" echoes in the past. Lastly, the midday summer population was found to be too high for polar mesosphere summer echoes and too early for plasma instabilities. It is proposed that these SuperDARN echoes are produced either from contribution from meteors trails or by neutral turbulence which is suspected (from other work) to be present near 100 km. The properties of the midday summer population resembles those of meteor trails as they have the same power, and the same altitude and have high summer occurrence as expected for meteors. Their late morning occurrence could be due to particular look direction of individual radars which may change the occurrence statistics in the presence of meteor showers. With respect to neutral turbulence, the drift of the midday summer population is similar to that of neutral wind

Fundamentals of collisionless shocks for astrophysical application, 1. Non-relativistic shocks

A comprehensive review is given of the theory and properties of nonrelativistic shocks in hot collisionless plasmas—in view of their possible application in astrophysics. Understanding non-relativistic collisionless shocks is an indispensable step towards a general account of collisionless astrophysical shocks of high Mach number and of their effects in dissipating flow-energy, in heating matter, in accelerating particles to high—presumably cosmic-ray—energies, and in generating detectable radiation from radio to X-rays. Non-relativistic shocks have Alfvénic Mach numbers {{\fancyscript{M}}_A\ll \sqrt{m_i/m_e}(\omega_{pe}/\omega_{ce})} , where m i /m e is the ion-to-electron mass ratio, and ω pe , ω ce are the electron plasma and cyclotron frequencies, respectively. Though high, the temperatures of such shocks are limited (in energy units) to T < m e c 2. This means that particle creation is inhibited, classical theory is applicable, and reaction of radiation on the dynamics of the shock can be neglected. The majority of such shocks are supercritical, meaning that non-relativistic shocks are unable to self-consistently produce sufficient dissipation and, thus, to sustain a stationary shock transition. As a consequence, supercritical shocks act as efficient particle reflectors. All these shocks are microscopically thin, with shock-transition width of the order of the ion inertial length λ i = c/ω pi (with ω pi the ion plasma frequency). The full theory of such shocks is developed, and the different possible types of shocks are defined. Since all collisionless shocks are magnetised, the most important distinction is between quasi-perpendicular and quasi-parallel shocks. The former propagate about perpendicularly, the latter roughly parallel to the upstream magnetic field. Their manifestly different behaviours are described in detail. In particular, although both types of shocks are non-stationary, they have completely different reformation cycles. From numerical full-particle simulations it becomes evident that, on ion-inertial scales close to the shock transition, all quasi-parallel collisionless supercritical shocks are locally quasi-perpendicular. This property is of vital importance for the particle dynamics near the quasi-parallel shock front. Considerable interest focusses on particle acceleration and the generation of radiation. Radiation from non-relativistic shocks results mainly in wave-wave interactions among various plasma waves. Non-thermal charged particles can be further accelerated to high energies by a Fermi-like mechanism. The important question is whether the shock can pre-accelerate shock-reflected particles to sufficiently high energies in order to create the seed-population of the non-thermal particles required by the Fermi mechanism. Based on preliminary full-particle numerical simulations, this question is answered affirmatively. Such simulations provide ample evidence that collisionless shocks with high-Mach numbers—even when non-relativistic—could probably by themselves produce the energetic seed-particle population for the Fermi-proces

Physics of Earth’s Radiation Belts

This open access book serves as textbook on the physics of the radiation belts surrounding the Earth. Discovered in 1958 the famous Van Allen Radiation belts were among the first scientific discoveries of the Space Age. Throughout the following decades the belts have been under intensive investigation motivated by the risks of radiation hazards they expose to electronics and humans on spacecraft in the Earth’s inner magnetosphere. This textbook teaches the field from basic theory of particles and plasmas to observations which culminated in the highly successful Van Allen Probes Mission of NASA in 2012-2019. Using numerous data examples the authors explain the relevant concepts and theoretical background of the extremely complex radiation belt region, with the emphasis on giving a comprehensive and coherent understanding of physical processes affecting the dynamics of the belts. The target audience are doctoral students and young researchers who wish to learn about the physical processes underlying the acceleration, transport and loss of the radiation belt particles in the perspective of the state-of-the-art observations

Laser Plasma Study through Simulation and Theory

Department of PhysicsStimulated Raman Scattering (SRS) is a fascinating physical phenomenon that arises from the interaction between a plasma medium and high-energy laser radiation. It involves the transfer of laser energy to plasma waves, resulting in the generation of new waves and the scattering of the incident laser beam. SRS is an important phenomenon in laser plasma interaction, with various applications in fields such as laser fusion, particle acceleration, and high-energy-density physics. The SRS process begins when a high-intensity laser beam interacts with a plasma medium. The laser energy excites plasma waves, which can be longitudinal or transverse depending on the direction of the laser polarization. These waves then undergo a resonance process, where they interact with the plasma ions and transfer energy to them. As a result, new waves are generated, and the incident laser beam is scattered in a different direction. One of the most significant features of SRS is its threshold behavior. SRS only occurs when the laser intensity exceeds a certain threshold value. Below this value, the plasma waves cannot reach the resonance condition and do not transfer energy to the plasma ions. Above the threshold value, however, the plasma waves grow exponentially, leading to a rapid increase in the scattered light intensity. SRS has various applications in laser plasma interaction. In laser fusion, SRS can be a significant obstacle as it leads to the loss of laser energy and can damage the laser system. Researchers have developed various methods to mitigate SRS, such as using frequency conversion techniques, plasma shaping, and polarization smoothing. In particle acceleration, SRS can be used to generate high-energy electron beams. By controlling the laser intensity and plasma conditions, researchers can create plasma wakefields that accelerate charged particles to high energies. Plasma density diagnostics are crucial to understanding the laser plasma interaction process. One diagnostic method involves using a probe laser to measure the plasma density through the interaction with the plasma electrons. Other diagnostic methods include interferometry, Thomson scattering, and Langmuir probes. Raman scattering diagnostics are a powerful tool for measuring the plasma density in a wide range of applications. This technique relies on the inelastic scattering of light from the plasma, which results in a shift in the frequency of the scattered light. By measuring the frequency shift, researchers can determine the plasma density and gain insight into the plasma???s behavior. Overall, Raman scattering diagnostics are a powerful tool for measuring plasma density in a wide range of applications. These techniques can provide valuable insight into the plasma???s behavior and are essential for the development of advanced plasma technologies. Ongoing research continues to improve the sensitivity and accuracy of Raman scattering diagnostics, ensuring that these techniques remain at the forefront of plasma research. Plasma dipole oscillations are a type of collective motion that can occur in a plasma medium when it is excited by an external electromagnetic field. These oscillations result from the motion of the plasma electrons in response to the electromagnetic field, creating a dipole moment that oscillates at a characteristic frequency. Plasma dipole oscillations are an important phenomenon in plasma physics and have various applications, including as a radiation source for plasma diagnostics. Plasma dipole oscillations can also act as a radiation source for plasma diagnostics. When the dipole moment of the plasma oscillates, it generates electromagnetic radiation at the same frequency. This radiation can be in the THzband depending on the plasma parameters. This characteristics create new diagnostic method for plasma density. More easily usage of PDO method, we shot the laser pulse obliquely. The magnetization of the PDO induces the formation of three modes in gyrating electrons: the upper hybrid (H) mode, the right circular mode (R), and the left circular mode (L). The H-mode acts as a resonance point that prevents transmission to the vacuum, whereas X-modes can be transmitted through the plasma. The H-mode diminishes as the magnetic field increases, while X-modes become more prominent. This results in more energy being extracted from the PDO in the form of radiation. This effect is demonstrated by the effective flow, where in the weak field regime, electrons are well organized, resulting in effective longitudinal flow, while in the strong field regime, electron phases are randomized, and circular flows prevail, forming X-modes instead of H-mode.clos

Physics of Earth’s Radiation Belts : Theory and Observations

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