Production of Ultrarelativistic Particles by Large-Amplitude Plasma Waves

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We have studied "production of ultrarelativistic particles by large-amplitude plasma waves" with theory and computer simulations. Our work may be summarized as follows.1)By using a one-dimension (one space coordinate and three velocity components), relativistic, electromagnetic, particle simulation code, we have studied the wave propagation and particle acceleration in electron-positron-ion plasmas. We have found that a magnetosonic shock wave, propagating obliquely to an external magnetic field can accelerate some positrons to ultrarelativistic energies. Also, we presented a theory for this acceleration mechanism. in the simulations, positrons with their Lorentz factors γ〜1000 have been observed.2)We investigated theoretically and numerically the acceleration of nonthermal, fast ions by an oblique shock wave. With test particle simulations, it has been demonstrated that some fast ions can be accelerated from γ〜1 to γ〜100. The evolution of energy and momentum distribution functions has also been examined. In the momentum space, these fast ions spread along a hyperbola.3)We theoretically investigated the electron acceleration to ultrarelativistic energies in detail. We obtained a simple expression for the maximum energy accelerated by a shock wave. The theory and simulation results were in good agreement.4)A three-dimension, electrostatic particle simulation code was used to study the ion Bernstein waves in a thermal equilibrium plasma. It is found that autocorrelation functions of these electric fields are damped if the plasma contains multiple ion species.5)In connection with these studies, we have theoretically investigated the structure and propagation of linear and nonlinear magnetohydrodynamic waves.