Download or read book Stochastic Acceleration of Electrons by Turbulence in Solar Flares written by Qingrong Chen and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Solar flares are among the most powerful explosions and most efficient particle accelerators in the solar system. The model of stochastic acceleration by plasma turbulence has been very instrumental in explaining the observed high-energy radiations and particles from solar flares. In this thesis, we aim to better constrain the electron acceleration and scattering processes by turbulence from hard X-ray imaging spectroscopic observations of solar flares. By utilizing the leaky box Fokker-Planck equation and the thick target equation describing particle acceleration and transport, we derive analytical formulas for the stochastic acceleration model quantities directly in terms of the accelerated and escaping particle spectra. Based on the hard X-ray radiating electron flux spectral images via regularized inversion, we determine the timescales for electron escape, pitch angle scattering, energy diffusion, and direct acceleration in two intense solar flares with a high-energy loop-top coronal source observed by the RHESSI mission. The existence of distinct coronal hard X-ray sources up to 100-150 keV in the impulsive phase indicates efficient confinement of high-energy electrons in the corona. The results that the electron escape time increases with energy and the acceleration time and scattering time exhibit very different energy dependences contradict existing predictions for stochastic acceleration due to wave-particle resonant interactions. The discrepancy between the observations and the acceleration model could be alleviated if the turbulence spectrum is much steeper than commonly assumed. A more plausible explanation for such events is that the escape of electrons from the loop-top acceleration region is not diffusive in nature due to scattering, but is affected by magnetic mirroring.
Download or read book Stochastic Acceleration in Electron dominated Solar Flares written by Brian Taewon Park and published by . This book was released on 1996 with total page 246 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Acceleration of Electrons and Ions by Strong Lower Hybrid Turbulence in Solar Flares written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-29 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the outstanding problems in solar flare theory is how to explain the 10-20 keV and greater hard x-ray emissions by a thick target bremsstrahlung model. The model requires the acceleration mechanism to accelerate approximately 10(exp 35) electrons sec(exp -l) with comparable energies, without producing a large return current which persists for long time scales after the beam ceases to exist due to Lenz's law, thereby, producing a self-magnetic field of order a few mega-Gauss. In this paper, we investigate particle acceleration resulting from the relaxation of unstable ion ring distributions, producing strong wave activity at the lower hybrid frequency. It is shown that strong lower hybrid wave turbulence collapses in configuration space producing density cavities containing intense electrostatic lower hybrid wave activity. The collapse of these intense nonlinear wave packets saturate by particle acceleration producing energetic electron and ion tails. There are several mechanisms whereby unstable ion distributions could be formed in the solar atmosphere, including reflection at perpendicular shocks, tearing modes, and loss cone depletion. Numerical simulations of ion ring relaxation processes, obtained using a 2 1/2-D fully electromagnetic, relativistic particle in cell code are discussed. We apply the results to the problem of explaining energetic particle production in solar flares. The results show the simultaneous acceleration of both electrons and ions to very high energies: electrons are accelerated to energies in the range 10-500 keV, while ions are accelerated to energies of the order of MeVs, giving rise to x-ray emission and gamma-ray emission respectively. Our simulations also show wave generation at the electron cyclotron frequency. We suggest that these waves are the solar millisecond radio spikes. The strong turbulence collapse process leads to a highly filamented plasma producing many localized regions for particle acceleration and resulting in ...
Download or read book Particle Acceleration and Kinematics in Solar Flares written by Markus Aschwanden and published by Springer Science & Business Media. This book was released on 2013-03-09 with total page 233 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the last decade we entered a new exploration phase of solar flare physics, equipped with powerful spacecraft such as Yohkoh, SoHO, and TRACE that pro vide us detail-rich and high-resolution images of solar flares in soft X-rays, hard X -rays, and extreme-ultraviolet wavelengths. Moreover, the large-area and high sensitivity detectors on the Compton GRO spacecraft recorded an unprecedented number of high-energy photons from solar flares that surpasses all detected high energy sources taken together from the rest of the universe, for which CGRO was mainly designed to explore. However, morphological descriptions of these beau tiful pictures and statistical catalogs of these huge archives of solar data would not convey us much understanding of the underlying physics, if we would not set out to quantify physical parameters from these data and would not subject these measurements to theoretical models. Historically, there has always been an unsatisfactory gap between traditional astronomy that dutifully describes the mor phology of observations, and the newer approach of astrophysics, which starts with physical concepts from first principles and analyzes astronomical data with the goal to confirm or disprove theoretical models. In this review we attempt to bridge this yawning gap and aim to present the recent developments in solar flare high-energy physics from a physical point of view, structuring the observations and analysis results according to physical processes, such as particle acceleration, propagation, energy loss, kinematics, and radiation signatures.
Download or read book Physical Processes in Solar Flares written by B.V. Somov and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 255 pages. Available in PDF, EPUB and Kindle. Book excerpt: Solar flares are very complex electromagnetic phenomena of a cataclysmic nature. Particles are accelerated to very high velocities and a variety of physical processes happen inside and outside flares. These processes can be studied by a large number of techniques from Earth and from space. The aim is to discover the physics behind solar flares. This goal is complicated because information about the flare mechanism can be obtained only in an indirect way by studying the secondary effects. This book provides three stages in the solution of the solar flare problem. Chapter one describes the connection between observational data and theoretical concepts, where it is stressed that next to investigating flares, the related non-stationary large-scale phenomena must be studied as well. The second chapter deals with secondary physical processes, in particular the study of high-temperature plasma dynamics during impulsive heating. The last chapter presents a model built on the knowledge of the two previous chapters and it constructs a theory of non-neutral turbulent current sheets. The author believes that this model will help to solve the problem of solar flares. For solar physicists, plasma physicists, high-energy particle physicists.
Download or read book Acceleration of Electrons and Ions by Strong Lower hybrid Turbulence in Solar Flares written by and published by . This book was released on 1994 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stochastic Acceleration of Solar Flare Protons written by Stanford University. Institute for Plasma Research and published by . This book was released on 1978 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: Consider the acceleration of solar flare protons by cyclotron damping of intense Alfven wave turbulence in a magnetic trap. The energy diffusion coefficient D sub EE is computed for a near-isotropic distribution of super-Alfvenic protons and a steady-state solution for the particle spectrum is found for both transit-time and diffusive losses out of the ends of the trap. The acceleration time to a characteristic energy of about 20 Mev/nucl can be as short as 10 sec. From phenomenological arguments one can infer that the Alfven wave spectrum has a 1/omega-squared frequency dependence and that the correlation time of the turbulence lies in the range .0005s
Download or read book Particle Acceleration and Trapping in Solar Flares written by G. Trottet and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt: These are the Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares. The Workshop was held on June 23-26,1986, at the city hall of Aubigny-sur-Nere (France), near Bourges and near the Nan
Download or read book Solar Energetic Particles written by Donald V. Reames and published by Springer. This book was released on 2017-03-10 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt: This concise primer introduces the non-specialist reader to the physics of solar energetic particles (SEP) and systematically reviews the evidence for the two main mechanisms which lead to the so-called impulsive and gradual SEP events. More specifically, the timing of the onsets, the longitude distributions, the high-energy spectral shapes, the correlations with other solar phenomena (e.g. coronal mass ejections), as well as the all-important elemental and isotopic abundances of SEPs are investigated. Impulsive SEP events are related to magnetic reconnection in solar flares and jets. The concept of shock acceleration by scattering on self-amplified Alfvén waves is introduced, as is the evidence of reacceleration of impulsive-SEP material in the seed population accessed by the shocks in gradual events. The text then develops processes of transport of ions out to an observer. Finally, a new technique to determine the source plasma temperature in both impulsive and gradual events is demonstrated. Last but not least the role of SEP events as a radiation hazard in space is mentioned and a short discussion of the nature of the main particle telescope designs that have contributed to most of the SEP measurements is given.
Download or read book Combined Modeling of Acceleration Transport and Hydrodynamic Response in Solar Flares 1 The Numerical Model written by and published by . This book was released on 2009 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: Acceleration and transport of high-energy particles and fluid dynamics of atmospheric plasma are interrelated aspects of solar flares, but for convenience and simplicity they were artificially separated in the past. We present here self consistently combined Fokker-Planck modeling of particles and hydrodynamic simulation of flare plasma. Energetic electrons are modeled with the Stanford unified code of acceleration, transport, and radiation, while plasma is modeled with the Naval Research Laboratory flux tube code. We calculated the collisional heating rate directly from the particle transport code, which is more accurate than those in previous studies based on approximate analytical solutions. We repeated the simulation of Mariska et al. with an injection of power law, downward-beamed electrons using the new heating rate. For this case, a -10% difference was found from their old result. We also used a more realistic spectrum of injected electrons provided by the stochastic acceleration model, which has a smooth transition from a quasi-thermal background at low energies to a non thermal tail at high energies. The inclusion of low-energy electrons results in relatively more heating in the corona (versus chromosphere) and thus a larger downward heat conduction flux. The interplay of electron heating, conduction, and radiative loss leads to stronger chromospheric evaporation than obtained in previous studies, which had a deficit in low-energy electrons due to an arbitrarily assumed low-energy cutoff. The energy and spatial distributions of energetic electrons and bremsstrahlung photons bear signatures of the changing density distribution caused by chromospheric evaporation. In particular, the density jump at the evaporation front gives rise to enhanced emission, which, in principle, can be imaged by X-ray telescopes. This model can be applied to investigate a variety of high-energy processes in solar, space, and astrophysical plasmas.
Download or read book Stochastic Forces on Electrons in the Solar Flare Plasma written by Claudia-Veronika Meister and published by . This book was released on 1994 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Radio and X Ray Evidence for Electron Acceleration in Solar Flares written by R. T. Stewart and published by . This book was released on 1982 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: Radio and X-ray observations, as well as gamma-ray and interplanetary electron observations, are briefly reviewed for evidence of electron acceleration during solar flares. The evidence suggests that in some large flares a second stage of particle acceleration takes place where ions and electrons are accelerated to very high energies. This second stage follows no more than several minutes after the first or impulsive stage, which occurs during the initial minute or so of the solar flare. During the impulsive phase electrons are accelerated to energies of approximately approx. 10-100 keV, probably by bulk energization, where stored magnetic energy is converted into thermal energy. Energy-loss arguments favor the electrons having a quasi-thermal (near-Maxwellian) electron velocity distribution. During large flares second-phase electrons are accelerated to much higher energies, approx. 10 MeV, and appear to have a power-law velocity distribution. The second-stage acceleration mechanism may be associated with a coronal shock wave, but so far there is no clear evidence that electrons with energies> or = 100 keV are directly associated with a shock wave. (Author).
Download or read book Physics of the Solar Corona written by Markus Aschwanden and published by Springer Science & Business Media. This book was released on 2004-09 with total page 888 pages. Available in PDF, EPUB and Kindle. Book excerpt: A thorough introduction to solar physics based on recent spacecraft observations. The author introduces the solar corona and sets it in the context of basic plasma physics before moving on to discuss plasma instabilities and plasma heating processes. The latest results on coronal heating and radiation are presented. Spectacular phenomena such as solar flares and coronal mass ejections are described in detail, together with their potential effects on the Earth.
Download or read book Solar Flare Loops Observations and Interpretations written by Guangli Huang and published by Springer. This book was released on 2018-01-31 with total page 437 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides results of analysis of typical solar events, statistical analysis, the diagnostics of energetic electrons and magnetic field, as well as the global behavior of solar flaring loops such as their contraction and expansion. It pays particular attention to analyzing solar flare loops with microwave, hard X-ray, optical and EUV emissions, as well as the theories of their radiation, and electron acceleration/transport. The results concerning influence of the pitch-angle anisotropy of non-thermal electrons on their microwave and hard X-ray emissions, new spectral behaviors in X-ray and microwave bands, and results related to the contraction of flaring loops, are widely discussed in the literature of solar physics. The book is useful for graduate students and researchers in solar and space physics.
Download or read book The Stochastic Acceleration of Plasma Particles in Solar Flares written by Timothy Q. Donaghy and published by . This book was released on 1999 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Energetic Electrons in Impulsive Solar Flares written by David Allen Batchelor and published by . This book was released on 1984 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Thermal nonthermal Approach to Solar Flares written by Stephen G. Benka and published by . This book was released on 1991 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt:
