In this paper, a plasma sheath containing primary electrons, cold positive ions, and secondary electrons is studied using a one‐dimensional fluid model in which the primary electrons are described by ...q‐non‐extensive distribution according to the Tsallis statistics. Based on the Sagdeev potential method and the current balance relation, a modified sheath criterion, and floating potential are established theoretically. The effect of secondary electron emission on q‐non‐extensive plasma sheath characteristics have been numerically examined. A significant change is observed in the quantities characterizing the non‐extensive plasma sheath with the presence of the secondary electrons. It is found that the sheath properties with super‐extensive distribution (q<1) and sub‐extensive distribution (q>1) are different compared with plasma sheath with Maxwell distribution (q=1).
The structure of a plasma sheath has been investigated in front of a caesium‐coated metallic plate, using a simple theoretical model. Along with the electrons, the plasma is composed of multi‐species ...of positive ions, and surface and volume produced negative ions. While the volume produced negative ions are common in many plasma processing chambers, the surface produced negative ions are of critical importance, especially to the Neutral Beam Injection (NBI) systems. The surface negative ions are produced via the coated metallic plate. With a single species of positive ion, the Bohm criterion, which determines the sheath edge potential, is multi‐valued for a specific range of electronegativity (α0$$ {\alpha}_0 $$). The width of the multi‐valued region has been reported to increase with the surface production yield (δ$$ \delta $$). Calculations are done for hydrogen plasma with a slight admixture of a second gas such as argon. Besides discussing the differences brought in by the mere presence of a second ion, the paper highlights the importance of the positive ion current density in determining the Bohm criterion. In addition, the effect of three species of positive ions in the surface production process has been discussed.
ABSTRACT In astrophysical plasmas, the magnetic field line random walk (FLRW) plays an important role in guiding particle transport. The FLRW behavior is scaled by the Kubo number for rms magnetic ...fluctuation b, large-scale mean field , and coherence scales parallel ( ) and perpendicular ( ) to . Here we use a nonperturbative analytic framework based on Corrsin's hypothesis, together with direct computer simulations, to examine the R-scaling of the FLRW for varying B0 with finite b and isotropic fluctuations with , instead of the well-studied route of varying for . The FLRW for isotropic magnetic fluctuations is also of astrophysical interest regarding transport processes in the interstellar medium. With a mean field, fluctuations may have variance anisotropy, so we consider limiting cases of isotropic variance and transverse variance (with bz = 0). We obtain analytic theories, and closed-form solutions for extreme cases. Padé approximants are provided to interpolate all versions of theory and simulations to any B0. We demonstrate that, for isotropic turbulence, Corrsin-based theories generally work well, and with increasing R there is a transition from quasilinear to Bohm diffusion. This holds even with bz = 0, when different routes to are mathematically equivalent; in contrast with previous studies, we find that a Corrsin-based theory with random ballistic decorrelation works well even up to R = 400, where the effects of trapping are barely perceptible in simulation results.
Nonrelativistic quantum mechanics is commonly formulated in terms of wavefunctions (probability amplitudes) obeying the static and the time-dependent Schrödinger equations (SE). Despite the success ...of this representation of the quantum world a wave–particle duality concept is required to reconcile the theory with observations (experimental measurements). A first solution to this dichotomy was introduced in the de Broglie–Bohm theory according to which a pilot-wave (solution of the SE) is guiding the evolution of particle trajectories. Here, I propose a geometrization of quantum mechanics that describes the time evolution of particles as geodesic lines in a curved space, whose curvature is induced by the quantum potential. This formulation allows therefore the incorporation of all quantum effects into the geometry of space–time, as it is the case for gravitation in the general relativity.
Sheath region of an electronegative magnetized plasma consisting of q-nonextensive electrons, Boltzmann distributed negative ions and positive ions with finite temperature is investigated by using a ...steady state fluid model. Considering Sagdeev's pseudo potential method, a modified Bohm criterion is derived. Taking into account the new formation criterion, the fluid model is then solved numerically and the density distribution of charged particles in the sheath region is studied for different values of the initial positive ion velocity at the sheath edge.
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