Dust-ion-acoustic damped solitary waves and shocks in laboratory and Saturn's E-ring magnetized nonthermal dusty plasmas with anisotropic ion pressure and dust-charge fluctuation

We study the oblique propagation of weakly nonlinear dust-ion-acoustic (DIA) solitary waves (SWs) and shocks in collisional magnetized nonthermal dusty plasmas that are relevant in laboratory and space (Saturn's E-ring) environments. We consider plasmas to be composed of $q$-nonextensive hot electrons, thermal positive ions, and immobile negatively charged dust grains immersed in a static magnetic field and take into account the effects of ion creation (source), and ion loss (sink), ion-neutral and ion-dust collisions, anisotropic ion pressure and dust-charge fluctuations on the evolution of small-amplitude SWs and shocks. The ion-neutral collision enhancement equilibrium dust-charge number is self-consistently determined using Newton's Raphson method. We found that in laboratory dusty plasmas with adiabatic dust-charge variation [i.e., when the dust charging frequency ($\nu_{\rm{ch}}$) is much higher than the dust-plasma oscillation frequency ($\omega_{\rm{pd}}$)], the DIA solitary waves (DIASWs) get damped by the effects of the ion-dust and ion-neutral collisions, whereas the ion creation and ion loss leads to the amplification of solitary waves, and they appear as only compressive types with positive potential. On the other hand, in Saturn's E-ring plasmas, where the collisional and ion creation or ion loss effects are insignificant, the non-adiabaticity of dust-charge variation can give rise to the evolution of either damped DIASWs or DIA shocks, depending on the smallness of the ratios $\nu_{\rm{ch}}/\omega_{\rm{pd}}$ or $\omega_{\rm{pd}}/\nu_{\rm{ch}}$, respectively. Furthermore, two critical values of the nonextensive parameter $q$ exist, below (or above) which, the DIASWs and shocks can appear as rarefactive (or compressive) types. The characteristics of DIASWs and shocks are also analyzed numerically for parameters relevant to the laboratory and Saturn's E-ring plasmas.Comment: Total 19 pages and 21 Figures with some Figure number has subplot

Trophic transfer of mercury in the fish species from Lake Phewa, Pokhara, Nepal

This study represents the first attempt to quantify concentrations of mercury and its trophic transfer along the food chain, in one of the lakes in Nepal, Lake Phewa. Stomach content analysis and stable isotopes of nitrogen (δ15N) and carbon (δ13C) were used as an index of trophic level and carbon source and were used to study bioaccumulation and biomagnifications of mercury in Nile Tilapia (Oreochromis niloticus), African magur (Clarias gariepinus), Sahar (Tor putitora) and Chuche Baam (Mastacembelus armatus) . Metal concentration in water and in the gill and liver of these fish species were examined. Muscles samples of the largest among each species were analyzed to identify the concentration of Persistant Organic Pollutants (POPs). The diet of O. niloticus were dominated by aquatic plants, regardless the size, whereas in other three species, aquatic insects, crustacea, fish were dominated in the diet. The mean and maximum value of total mercury (THg mg kg-1 w.w.) concentrations were 0.071 and 0.32 for C. gariepinus, 0.031 and 0.081 for O. niloticus, 0.116 and 0.21for T. putitora and 0.079 and 0.22 for M. armatus. The relationship between THg and total length and total weight were positive and significant in C. gariepinus and M. armatus. Age determination could not be done for any of the fish species. For none of the species, the value of δ15N and δ13C correlates with the total length of the fish, possibly because of few isotope analysis. The relationship between log THg and δ15N were with the present analysis, not significant for any of the species indicating no biomagnification. Since the THg level in all the fish species was consistently low, it will not pose any harm to the fish consuming community. In the food chain, M. armatus hold the top position and O. niloticus the bottom. Metal analysis of water, gill and liver showed the exposure of fish species to various trace metals. Except for high levels of manganese (Mn), the values were comparable to levels found in other lake and river system in Europe. Metabolites of DDT and Endosulfan sulfate were found in the muscle sample of fish, but at levels of low concern by the present regulations. The present study represents only 4 out of nearly 30 species so far registered in Lake Phewa. Further studies on Hg and pesticides in the most important fish species in Lake Phewa, as well as in the other lakes in the region, should be facilitated to improve risk assessment and enable a proper management in relation to pollutants in the fish populations of the lakes

Effects of collision and ion Mach number on magnetized plasma sheath with two species of positive ions

We study the effect of collision and ion Mach number in a magnetized plasma sheath having two species of positive ions using fluid model. It is assumed that both the ions are singly ionized and in thermal equilibrium, and the electrons obey Boltzmann distribution. Our work signifies that the collision greatly affects the ion densities, which explicitly affect space charge density, net current density and the transverse drift of ions. On increasing the collisional frequency, ions accumulation point and current saturation point shift towards the sheath entrance (away from the wall). The ion Mach number affects potential profile and velocity profiles of both ion species. The magnitude of wall potential increases from 34 V to 45 V with the increase in ion Mach number from 0.3 to 0.9. Furthermore, it is shown that the effect of collisional force and Lorentz force is reduced at the sheath entrance by increasing the ion Mach number, which helps to control the flux of particles, momentum flow and energy flow towards the wall

Kinetic-theory-based investigation of electronegative plasma–wall transition with two populations of electrons

Abstract Kinetic theory has been employed to investigate the magnetized plasma-sheath structure and its characteristics in the presence of more than one species of negatively charged particles: hot electrons, cold electrons, and negative ions. The cold electrons and negative ions are considered to obey a Maxwellian distribution, whereas the hot electrons follow a truncated Maxwellian distribution. The Bohm sheath condition has been extended for the case of more than one species of negatively charged particles, in which the concentration of hot electrons has a crucial role in achieving the Bohm velocity. The thermal motion of hot electrons is much higher compared to cold electrons and negative ions, such that the variation of hot electron concentrations and the temperature ratio of hot to cold electrons play a key role in the determination of the plasma-sheath parameters: particle densities, electrostatic potential, the flow of positive ions towards the wall, and sheath thickness. We have estimated the deviation of the resultant drift velocity of positive ions on the plane perpendicular to the wall from the parallel component at the presheath–sheath interface. It is found that the deviation between the two velocity components increases with an increase in the obliqueness of the magnetic field. Furthermore, the results obtained from the kinetic trajectory simulation model are compared with the results obtained using a fluid model; the results are qualitatively similar, although the potential varies by less than 4% in terms of the magnitude at the wall.</jats:p

Electronegative magnetized plasma sheath properties in the presence of non-Maxwellian electrons with a homogeneous ion source

Abstract The three-fluid model was employed to study electronegative magnetized plasma sheath properties in the presence of non-Maxwellian electrons. The Bohm condition for the electronegative magnetized plasma was extended in the presence of a homogeneous ionization source term and an ion-neutral collision force. The effect of the following physical parameters: the degree of non-Maxwellian electrons, ion-neutral collisions, obliqueness of the magnetic field and source frequency on the plasma sheath parameters are numerically analyzed and presented. It was found that the magnitude of the potential increased in all cases and hence the velocity of the ions increased towards the wall. The plasma sheath parameters were not significantly varied about 2λ De from the presheath—sheath interface, but after that, the sheath parameters abruptly changed towards the wall. The effect of ion-neutral collisions and the obliqueness of the magnetic field on the potential distribution, net charge density and drift velocity of ions are discussed. Furthermore, a comparison of plasma sheath characteristics with and without the ion source term is systematically presented.</jats:p