Contributions to Plasma Physics最新文献

The accurate definition and powerful evaluation modeling of the various generalized Fermi–Dirac and Bose–Einstein functions remain a challenging problem in various areas of physics. In this study, we develop a general analytical technique for accurately calculating logarithmic and double Fermi–Dirac and Bose–Einstein functions. The obtaining analytical formulae are established by considering the binomial expansion theorem. The obtained expressions are valid in chemical potential values between -∞ <μ <0 and have been designated as explicit form features, high precision, and less computing time. The calculation results are tabularly illustrated to show the consistency of the analytical relations analysis under the effect of parameters. Based on a comprehensive analysis of the results, they are potentially useful in applications to evaluate thermionic emission and astrophysics problems.

A computational study is presented on laser wakefield acceleration (LWFA) in bubble regime with the use of ultrashort laser pulse propagating in an under-dense plasma. The Particle-In-Cell simulations are performed to investigate the bubble wakefield acceleration of electrons realized by the incidence of an intense laser beam on cold, under-dense plasma in two-dimensional geometry. Different simulations are carried out and the results are compared for the beams with trapezoidal and Gaussian temporal pulse profiles having almost equal but slightly different energy contents. Focus is given to plasma density modulation, wakefield strength, electrons self-injection, energy spectrum of accelerated electrons, the effect of an external longitudinal magnetic field and the study of pump depletion length and dephasing length in bubble regime with respect to these laser pulse profiles. Two limiting cases of the trapezoidal pulse, that is, triangular and rectangular pulses, are also discussed for better understanding of the role of steepness and plateau region in the laser pulse profile to the bubble wakefield acceleration. Since down ramp density gradient plays a crucial role for the generation of high-quality electron beam in plasma wakefield acceleration as well as in LWFA, three different adjustments on the down ramp length determining three different density gradients are discussed for uncovering the role of trapezoidal laser pulse in LWFA.

Edge localized modes resulted from magnetohydrodynamic (MHD) instabilities in the pedestal region are a significant concern for future tokamaks. In this work, Ci-Liu-Ti (CLT), an MHD code in the three-dimensional toroidal geometry, is applied for the linear simulation of the ideal pedestal MHD instabilities. The simulations are performed for the experimental advanced superconducting tokamak-like elongated divertor configuration with large triangularity, which is generated by the high-accuracy free-boundary equilibrium solver (CLT-EQuilibrium, i.e., CLT-EQ) developed recently. The present work focuses on the influence of the magnetic shear, which is scanned by adjusting the pedestal current with a fixed pedestal pressure profile. As the pedestal current increases, both the local (S_local) and global (S_global) magnetic shear decrease. The ballooning mode is destabilized along with the decrease of S_local, and stabilized when S_local is negative for the whole region of bad curvature, which implies the access of the second stable region. Further increase of the pedestal current leads to the destabilization of the kink mode, which is stabilized again until S_global is negative at the location of significant gradient of current density. The simulated results are consistent with the findings in Radovanovic et al. Nucl. Fusion 62 (2022) 086004 and C. K. Sun et al. Phys. Plasmas 25 (2018) 082106, which indicates the availability of CLT in the linear simulation of the ideal pedestal instabilities.

We summarize the method of hydrodynamic approximation for weakly ionized plasmas developed with Klimontovich in 1962 and give a generalization to many—component systems using Onsagers matrix theory and including dispersion effects. We develop the conductivity theory of complex plasma and electrolyte mixtures based on the model of charged hard spheres with given non-additive contact distances, including frequency-dependent electric fields. These generalizations are made with the aim to allow applications to complex natural systems as atmospheric plasmas and seawater. Finally, we give as an example a numerical calculation of the single ion conductivities of a six-component seawater model.

The scattering dynamics of electron capture in $��e^{+}�$-H(1 s) scattering under dense semi-classical plasma (DSCP) environments has been investigated theoretically. Coupled multi-channel two-body Lippmann-Schwinger equations have been solved by retaining $��e^{+}�$+H(1 s) and p + Ps(1 s) channels to calculate the cross sections (CS) of the electron capture process at intermediate and high incident energies. The effective interaction of the plasma charged particles is modelled by a pseudopotential which is a function of two parameters, namely the plasma screening strength and the de Broglie wavelength. A detailed study is made to explore the changes in the CSs of the above-mentioned process with respect to the variation in the plasma screening strength and de Broglie wavelength. Significant changes are found to take place, when the screening strength and the de Broglie wavelength are varied. Specifically, the sharp minimum in the differential CS moves toward the forward direction with increasing de Broglie wavelength at a given screening strength.

In this work, emission spectra measurements from direct current (DC) reverse-brush discharge plasmas were used to elucidate the energy level transition processes corresponding to each spectral line based on the mechanism of emission spectrum generation. The axial distribution patterns of the spectral line intensity and the electron excitation temperature in the electrode gap and post-cathode space were systematically investigated. By comparing the acquired experimental results, it was observed that both the relative intensity of the plasma emission spectra and the electron excitation temperature in the electrode gap were higher than in the post-cathode space, while their axial distribution trends exhibited an initial increase followed by a decrease. Additionally, the impact of the discharge gas pressure, reverse-brush electrode thickness, and the number of electrode openings on the emission spectral line intensity and electron excitation temperature in the electrode gap were explored. Explanations for the underlying physical mechanisms were also provided.

(a) Electron current density, z-component; (b) Electric field intensity (V/m); filament line: electron flow. Fig.6 of the paper by Yiqun Ma et al. https://doi.org/10.1002/ctpp.202300169

Partially detached H-modes are the baseline regime for the future ITER operation. The ASDEX Upgrade partially detached H-mode is modeled using the SOLPS-ITER code with drifts enabled and compared with experimental data. For the first time, boron (B) impurity is simulated in the Scrape-off layer (SOL) and divertor. A comparison between divertor diagnostics and discrepancies between Langmuir probe and Divertor Thomson scattering/Stark broadening diagnostic are discussed. In the modeling, experimental target profiles are reproduced if the experimental level of radiation in the SOL and divertor is achieved using nitrogen (N) impurity seeding. Bolometry measurements detect substantial radiation from the partially detached outer strike point. With B radiation, this maximum in bolometry data is reproduced in the modeling, which is not possible with N alone.

A first principle molecular dynamics (MD) simulation study on the nonlinear excitations in a quasi-localized state of a Yukawa system is presented to validate the findings of the nonlinear quasi-localized charge approximation (QLCA) model. Unlike solids or gases, quasi-localized states lack certain simplifying features, such as the ability to assume a fixed shape or volume, and they combine large displacements with strong interactions, further complicating the theoretical underpinnings of their behavior. In a recent paper [P. Kumar and D. Sharma, Physics of Plasmas 30 (2023)], the nonlinear QLCA model was applied to characterize the nonlinear excitations in a quasi-localized state of a Yukawa system, as existing continuum models have shown limited success in this regime. The simulation data presented with the screening and coupling parameters show a close agreement with the QLCA model findings. The MD simulations validate the prediction made by the QLCA model that the properties of a soliton remain unaffected by variations in the coupling parameter. The prediction made by QLCA regarding the formation of multiple solitons at higher screening parameter values has also been confirmed by the MD simulation data. The possibility of the formation of rarefactive solitons at relatively high screening parameter values within the QLCA model is also discussed.