Monthly Archives: August 2015

Thermodynamics of Yukawa fluids near the one-component-plasma limit

Thermodynamics of weakly screened (near the one-component-plasma limit) Yukawa fluids in two and three dimensions is analyzed in detail. It is shown that the thermal component of the excess internal energy of these fluids, when expressed in terms of the properly normalized coupling strength, exhibits the scaling pertinent to the corresponding one-component-plasma limit (the scalings differ considerably between the two- and three-dimensional situations). This provides us with a simple and accurate practical tool to estimate thermodynamic properties of weakly screened Yukawa fluids. Particular attention is paid to the two-dimensional fluids, for which several important thermodynamic quantities are calculated to illustrate the application of the approach.

Parametric study of a Schamel equation for low-frequency dust acoustic waves in dusty electronegative plasmas

In this paper, our attention is first concentrated on obliquely propagating properties of low-frequency (ω ≪ ω cd ) “fast” and “slow” dust acoustic waves, in the linear regime, in dusty electronegative plasmas with Maxwellian electrons, kappa distributed positive ions, negative ions (following the combination of kappa-Schamel distribution), and negatively charged dust particles. So, an explicit expression for dispersion relation is derived by linearizing a set of dust-fluid equations. The results show that wave frequency ω in long and short-wavelengths limit is conspicuously affected by physical parameters, namely, positive to negative temperature ion ratio (βp ), trapping parameter of negative ions (μ), magnitude of the magnetic field B 0 (via ωcd ), superthermal index ( κ n , κ p ), and positive ion to dust density ratio (δp ). The signature of the penultimate parameter (i.e., κn ) on wave frequency reveals that the frequency gap between the modes reduces (escalates) for k k c r ( k > k c r ), where kcr is critical wave number. Alternatively, for weakly nonlinear analysis, reductive perturbation theory has been used to construct 1D and 3D Schamel Korteweg-de Vries (S-KdV) equations, whose nonlinearity coefficient prescribes only compressive soliton for all parameter values of interest. The survey manifests that deviation of ions from Maxwellian behavior leads intrinsic properties of solitary waves to be evolved in opposite trend. Additionally, at lower proportion of trapped negative ions, solitary wave amplitude mitigates, whilst the trapping parameter has no effect on both spatial width and the linear wave. The results are discussed in the context of the Earth's mesosphere of dusty electronegative plasma.

Jeans instability with exchange effects in quantum dusty magnetoplasmas

Jeans instability is examined in magnetized quantum dusty plasmas using the quantum hydrodynamic model. The quantum effects are considered via exchange-correlation potential, recoil effect, and Fermi degenerate pressure, in addition to thermal effects of plasma species. It is found that the electron exchange and correlation potential have significant effects over the threshold value of wave vector and Jeans instability. The presence of electron exchange and correlation effect shortens the time of dust sound that comparatively stabilizes the self gravitational collapse. The results at quantum scale are helpful in understanding the collapse of the self-gravitating dusty plasma systems.

Weak turbulence in dusty plasmas with collisional dust charging: Quasilinear wave-particle interaction

Author(s): Renato A. Galvão and Luiz F. Ziebell

Starting from the exact microscopic equations for an unmagnetized dusty plasma, where the dust charge is regarded as a new degree of freedom of the system, we present a self-consistent set of equations that is suitable for weak turbulence analyses, where we have considered that the dust is electrica…

[Phys. Rev. E 92, 023102] Published Thu Aug 13, 2015

Stability of an elliptical vortex in a strongly coupled dusty plasma

The stability of a long scale equilibrium vortex structure to short scale perturbations is studied in a strongly coupled dusty plasma in the framework of a generalized hydrodynamic model. It is shown that the free energy associated with the velocity shear of the vortex can drive secondary instabilities consisting of transverse shear waves when the resonance condition between the vortex rotation frequency and the secondary wave frequency is met. Such a process can transfer energy from the long scale vortex to the short scale secondary wave and thereby provide a saturation mechanism for long scale vortices in plasmas in a manner analogous to that in neutral fluids.

Soft mean spherical approximation for dusty plasma liquids: Level of accuracy and analytic expressions

The soft mean spherical approximation is employed for the study of the thermodynamics of dusty plasma liquids, the latter treated as Yukawa one-component plasmas. Within this integral theory method, the only input necessary for the calculation of the reduced excess energy stems from the solution of a single non-linear algebraic equation. Consequently, thermodynamic quantities can be routinely computed without the need to determine the pair correlation function or the structure factor. The level of accuracy of the approach is quantified after an extensive comparison with numerical simulation results. The approach is solved over a million times with input spanning the whole parameter space and reliable analytic expressions are obtained for the basic thermodynamic quantities.

Reaction-in-flight neutrons as a test of stopping power in degenerate plasmas

We present the first measurements of reaction-in-flight (RIF) neutrons in an inertial confinement fusion system. The experiments were carried out at the National Ignition Facility, using both Low Foot and High Foot drives and cryogenic plastic capsules. In both cases, the high-energy RIF ( E n > 15 MeV) component of the neutron spectrum was found to be about 10−4 of the total. The majority of the RIF neutrons were produced in the dense cold fuel surrounding the burning hotspot of the capsule, and the data are consistent with a compressed cold fuel that is moderately to strongly coupled ( Γ ∼ 0.6) and electron degenerate ( θ Fermi / θ e ∼ 4). The production of RIF neutrons is controlled by the stopping power in the plasma. Thus, the current RIF measurements provide a unique test of stopping power models in an experimentally unexplored plasma regime. We find that the measured RIF data strongly constrain stopping models in warm dense plasma conditions, and some models are ruled out by our analysis of these experiments.

Dual-mode resonant instabilities of the surface dust-acoustic wave in a Lorentzian plasma slab

The dual-mode resonant instabilities of the dust-acoustic surface wave propagating at the plasma-vacuum interfaces of the generalized Lorentzian dusty plasma slab are kinetically investigated. The dispersion relation is derived for the two propagation modes: symmetric and anti-symmetric waves. We have found that the temporal growth rate of the resonant instability increases with an increase of the slab thickness for both modes. Especially, the nonthermality of plasmas enhances the growth rate of the anti-symmetric resonant wave, and the nonthermal effect is enhanced as the slab thickness is increased. It is also found that the growth rate increases with increasing angular frequency of the rotating dust grain due to the enhanced resonant energy exchange.

Observation of the Rayleigh-Bénard convection cells in strongly coupled Yukawa liquids

Using “first principles” molecular dynamics simulation, we report for the first time the formation of Rayleigh-Bénard convection cells (RBCC) in two-dimensional strongly coupled Yukawa liquids, characterized by coupling strength Γ (ratio of average potential energy to kinetic energy per particle) and screening parameter κ (ratio of average inter-particle distance to Debye length). For typical values of (Γ, κ), existence of a critical external temperature difference is demonstrated, beyond which RBCC are seen to set in. Beyond this critical external temperature difference, the strength of the maximum convective flow velocity is shown to exhibit a new, hitherto unsuspected linear relationship with external temperature difference and with a slope independent of (Γ, κ). The time taken for the transients to settle down (τs ) to a steady state RBCC is found to be maximum close to the above said critical external temperature difference and is seen to reduce with increasing external temperature difference. For the range of values of (Γ, κ) considered here, τs ≈ 10 000–20 000 ω p d − 1 , where ωpd is dust plasma frequency. As Γ is increased to very high values, due to strong coupling effects, cells are seen to be in a transient state without attaining a steady state for as long as 100 000 ω p d − 1 , even for a very high external temperature difference. Role of system size, aspect ratio, and dust-neutral collisions has also been addressed.

Kinetic theory of dust ion acoustic waves in a kappa-distributed plasma

Using a kinetic theory approach, dust ion acoustic (DIA) waves are investigated in an unmagnetized collisionless plasma with kappa-distributed electrons and ions, and Maxwellian dust grains of constant charge. Both analytical and numerical results, the latter following from the full solution of the associated dispersion relation, are presented, and a comparison is made. The effects of the ion and electron spectral indices, as well as the species' density ( n e / n i ) and temperature ( T e / T i ) ratios, on the dispersion and damping of the waves are considered. In the long wavelength regime, increases in both the electron spectral index (κe ) and the dust density fraction (reduced f = n e / n i ) lead to an increase in phase velocity. The range in wavelength over which modes are weakly damped increases with an increase in T e / T i . However, the ion spectral index, κi , does not have a significant effect on the dispersion or damping of DIA waves.