16 research outputs found
Eigenmodes and growth rates of relativistic current filamentation instability in a collisional plasma
I theoretically found eigenmodes and growth rates of relativistic current
filamentation instability in collisional regimes, deriving a generalized
dispersion relation from self-consistent beam-Maxwell equations. For
symmetrically counterstreaming, fully relativistic electron currents, the
collisional coupling between electrons and ions creates the unstable modes of
growing oscillation and wave, which stand out for long-wavelength
perturbations. In the stronger collisional regime, the growing oscillatory mode
tends to be dominant for all wavelengths. In the collisionless limit, those
modes vanish, while maintaining another purely growing mode that exactly
coincides with a standard relativistic Weibel mode. It is also shown that the
effects of electron-electron collisions and thermal spread lower the growth
rate of the relativistic Weibel instability. The present mechanisms of
filamentation dynamics are essential for transport of homogeneous electron beam
produced by the interaction of high power laser pulses with plasma.Comment: 44 pages, 12 figures. Accepted for publication in Phys. Rev.
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Improved intra-species collision models for PIC simulations
In recent years, the authors have investigated methods to improve the effectiveness of modeling collisional processes in particle-in-cell codes. Through the use of generalized collision models, plasma dynamics can be followed both in the regime of nearly collisionless plasmas as well as in the hydrodynamic limit of collisional plasmas. They have developed a collision-field method to treat both the case of collisions between unlike plasma species (inter-species collisions), through the use of a deterministic, grid-based force, and between particles of the same species (intra-species collisions), through the use of a Langevin equation. While the approach used for inter-species collisions is noise-free in that the collision experienced by a particle does not require any random numbers, such random numbers are used for intra-species collisions. This gives rise to a stochastic cooling effect inherent in the Langevin approach. In this paper, the authors concentrate on intra-species collisions and describe how the accuracy of the model can be improved by appropriate corrections to velocity and spatial moments
Recursos minerais nĂŁo-metĂĄlicos
OS RECURSOS minerais nĂŁo-metĂĄlicos, embora muito importantes para o atendimento das necessidades da população e para o comĂ©rcio exterior, sĂŁo pouco contemplados pelas açÔes governamentais e ignorados pelo pĂșblico. Geralmente nĂŁo-incluĂda no planejamento territorial, a mineração de nĂŁo-metĂĄlicos no Brasil causa extensos impactos ambientais mal controlados. PropĂ”e-se uma ação coordenada de fomento e controle patrimonial e ambiental da mineração, que sĂł serĂĄ conseguida por ação polĂtica, a qual depende da formação abrangente dos profissionais da mineração e de sua maior comunicação com a totalidade da população.<br>NONMETALLIC mineral resources, albeit very important for the needs of the population and for exportation, are ill-favored by governmental actions and ignored by the public. Generally not included in territorial planning, the mining of nonmetallic minerals in Brazil produces extensive, ill-controlled environmental impacts. A coordinated action of promotion and control, both patrimonial and environmental of mining, is proposed. This will only be achieved by political action, which depends on a more comprehensive education of mining professionals and on a greater communication by them with the population as a whole