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Abstract:
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In the disertation, by the linear plasma theory we show that resonant electromagnetic (EM)micro-instabilities are excited by the two colliding plasmas which are interpenetrating eachother with the super-Alfv ́enic velocity, in the direction quasi-parallel to the magnetic field.The expected Rankine-Hugoniot shock conditions, naturally arise as a consequence of a highlyresonant interaction of ions with the instability. By using kinetic simulations, we find herethat such resonant instabilities appear in the linear stage, and we show how these instabilitiestrigger the shock formation during the non-linear stage.By theoretical modeling, we show how a magnetosonic soliton forms and leads to the periodicshock reformation and initiation of the return current of ions, which drives the EM upstreaminstability. We find that ions are being pre-accelerated by the upstream and shock instabilities ina mechanism that is similar to the diffusive shock acceleration (DSA). By our EM test particlesimulation runs we show that at quasi-parallel shocks, EM instabilities highly contribute toelectron pre-acceleration, leading to the formation of a power-law electron spectra through theFermi-like mechanism.By very long kinetic simulation runs, in this disertation we find that ions and electronsenter DSA in a similar number which is further applied in a model of non-linear DSA. Withinthis model, we obtain the theoretical particle spectra and we find the electron-to-proton ratioat high energies for the different Mach numbers. We show that the spectra of quasi-thermalparticles at the shock can be represented by a non-equilibriumκ-distribution. We find thatthe level of modification decreases andκ-index increases behind the shock, implying that theparticle distribution tends to become a Maxwellian. |