Contributions to Plasma Physics最新文献

This study investigates how spin polarization, arising from spin mismatch between electron populations, influences the propagation of kinetic Alfvén waves (KAWs) in a low-beta electron-ion plasma. By analyzing the impact of spin-polarized electron densities in distinct spin states, the research examines modifications to wave dispersion in both linear and nonlinear regimes. In the linear analysis, the study derives and examines the coupled dispersion relation for two dominant wave modes: one governed by Alfvénic dynamics and the other by acoustic interactions. The findings indicate that spin polarization increases the phase speed in the Alfvénic regime, while a larger spin mismatch significantly reduces the phase speed in the acoustic regime. Additionally, the interplay between perpendicular wave characteristics and ion gyration effects modifies wave dispersion, particularly for shorter wavelengths. The study also highlights the role of wave propagation direction in shaping frequency characteristics. In the nonlinear regime, the evolution of KAWs is analyzed using the Reductive Perturbation Technique, leading to a mathematical framework that describes solitary wave structures. The results show that spin polarization suppresses the amplitude and narrows the width of these solitons, while higher electron degeneracy counteracts these effects, contributing to their stabilization. Furthermore, wave obliqueness and the Mach number play a significant role in determining the spatial characteristics and energy distribution of the solitons. These insights provide a deeper understanding of KAW behavior in spin-polarized plasmas, which is relevant to space and astrophysical environments where such conditions prevail.

Using the Lee model code, numerical experiments were performed to compute the soft x-ray (SXR) yield as a function of the initial neon pressure for seven different energy plasma focus devices (NX2, INTI, UNU/ICTP, APF, NX1, PF7, PF24). In addition, the effect of operation voltage for four plasma focus devices (APF, NX2, UNU/ICTP, NX1) and the anode length for two plasma focus devices (NX1, NX2) on the soft x-ray yield (Y_sxr) versus pressure was studied and discussed. At experimental pressure, the computed current waveform was well fitted to the measured total current waveform for each device. Furthermore, the maximum discharge current, pinch current, axial and radial velocities, average pinch temperatures and densities, and pinch dimensions around the optimum pressure for the maximum Y_sxr were computed for the seven mentioned devices. The computed values obtained are within the temperature window required to generate H-like (1022 eV) and He-like (922 eV) plasmas. The computed Y_sxr are in good agreement with part of the experimental results. Moreover, experimental and computed values of the end axial speed (v_a), final inward shock speed (v_s), the speed factor (SF) and the current per cm of anode radius (ID) were compared for part of the considered devices.

The ice giant planets Uranus and Neptune are assumed to contain large amounts of planetary ices such as water, methane, and ammonia. The properties of mixtures of such ices at the extreme pressures and temperatures of planetary interiors are not yet well understood. Ab initio computer simulations have predicted that a number of ices exhibit a hydrogen superionic state and a doubly superionic state. Since the latter state has not yet been generated with experiments, we outline here two possible pathways for reaching and detecting such a state with dynamic compression experiments. We suggest X-ray diffraction as the principal tool for detecting when the material becomes doubly superionic and the sublattice of one of the heavy nuclei melts. That would require a temperature of $��\sim �$3500 K and pressures greater than $��\sim �$200 GPa for H$��{\hspace{0.17em}}_3�$NO$��{\hspace{0.17em}}_4�$, which we use as an example material here. Such conditions can be reached with experiments that employ an initial shock that is followed by a ramp compression wave. Alternatively, one may use triple-shock compression because a single shock does not yield sufficiently high densities.

This study explores how both an external magnetic field and finite particle size influence the diffusion characteristics of two-dimensional Yukawa systems. By employing the equilibrium molecular dynamics method, we calculate the mean-squared displacements of particles and the diffusion coefficients across a broad range of system parameters. It is well established that magnetic fields reduce the diffusion coefficient by constraining particle motion within the system. Our research shows that the effect of finite particle size on diffusion is influenced by the degree of magnetization, resulting in either increased or decreased diffusion coefficients depending on magnetic field strength.

Dynamic properties of two important exanples of binary and ternary ionic mixtures are studied using the self-consistent version of the method of moments. It is determined that in a $��H^{+}�-�D^{+}�$ mixture the lifetime of the roton branch of the system plasmon-roton mode is comparable or even shorter than the mode period, that is, that this branch is virtual or strongly decaying. In the ternary mixture $��D^{+}�-�T^{+}�{-}^3�{\mathrm{He}}^{�+�+�}�$ this branch's decrement is found to be smaller than its frequency, so that it becomes observable. Conditions are established for the mixture dielectric function to lose its analyticity in the complex frequency upper half-plane, and the relative contributions to the $��f�-�$ sum rule of the unique pole located on the positive part of the imaginary axis called the “ghost plasmon” and of other two poles located in the lower half-plane are found.

With a view to understanding some nonlinear properties of the ion-acoustic solitary waves (IASWs) like phase velocity, nonlinearity, amplitude and production of solitons in the $��A�r^{+}�$, $��F^{-}�$, and $��{\mathrm{SF}}_5^{-}�$ species plasma (referred to as $��A�r^{+}�$ plasma) as well as $��{\mathrm{SF}}_5^{+}�$, $��F^{-}�$, and $��{\mathrm{SF}}_5^{-}�$ species plasma (referred to as $��{\mathrm{SF}}_5^{+}�$ plasma) including nonthermal electrons and positrons under the influence o