Contributions to Plasma Physics最新文献

The impact of spatial and temporal evolution of nonlinear mixing of two Gaussian laser pulses propagating in plasma on generation of terahertz (THz) radiation have been investigated taking into account the ponderomotive nonlinearity. By calculating the modified electron density of plasma caused by the finite ponderomotive force of the pump lasers and using wave equation and paraxial ray approximation, two coupled governing equations for temporal and spatial pulse-width parameters have been derived. The electric field of the THz wave as a result of nonlinear current density induced by the beat ponderomotive force of the pulses was extracted. Combined effects of initial laser and plasma parameters on the behavior of self-compression and self-focusing as well as THz radiation generation were investigated. The numerical results indicated a considerable spatiotemporal compression takes place within a specific range of laser intensity, exhibiting a saturation intensity point where the compression process reaches its maximum extent. It is observed that the generated THz radiation also strongly depends on the spatiotemporal dynamics of the pump pulses. The maximum THz amplitude corresponds to the strongest pump pulse compression extent.

The high-density transient plasma, streaming from a pulsed plasma accelerator (PPA), was diagnosed with a Triple Langmuir probe (TLP) for spatial mapping of the stream in terms of plasma density and temperature. A contour plot for density and temperature shows a distinct form of a highly dense island of plasma with varied plasma temperatures. The formation of such highly dense islands can be correlated with the formation of distinct plasma structures, as observed in astrophysical plasmas and fusion plasma. The results of TLP were supported by the intensity variation derived from signals of a photodetector system. The plasma stream imaged with high-speed video camera also showed the density fluctuation inside the plasma stream. The estimated maximum density and temperature were ∼7.2 × 10²⁰ m⁻³ and ∼28 eV, respectively.

Because of the low rate of penetration (ROP) and high cost of traditional rotary rock breaking, it is important to explore some unconventional new rock breaking methods. High-voltage electrical pulse (HVEP) drilling has attracted much attention because of its advantages such as environmental protection, good borehole wall quality, and high rock breaking efficiency. This paper independently designs and builds a complete indoor experimental platform of HVEP electric breakdown, and selects the self-designed classic coaxial type and cross-type electrode bits to carry out laboratory experiments of HVEP rock-breaking, to truly reveal the rock breaking mechanism of HVEP drilling and further promote its industrial application. The influence of the anode structure of electrode bit, liquid insulation medium, drilling fluid circulation condition, and pulse voltage on rock breaking mechanism are investigated. The findings indicate that the bottom-hole morphology of the rock sample is related to the electrode bit structure. The S-type electrode bit has a certain discharge blind area, which is not conducive to the rock breaking of HVEP. With the increase of pre-charging voltage, the effective discharge rate (EDR) of both electrode bits increases gradually, trending towards 100% as the pre-charging voltage grows. Under non-circulating working conditions, greater conductivity of liquid medium results in a lower EDR of electrode bits. In all kinds of liquid media, under low voltage (pre-charging voltage <15 kV), the single pulse penetration depth (SPPD) under the non-circulating working condition is larger than that of the circulating condition, in contrast, at a higher voltage (pre-charging voltage >15 kV), the SPPD under the circulating condition is larger than that the non-circulating condition. To further observe the generation of plasma channel and the rock damage characterization of HVEP, this paper also establishes a three-dimensional numerical model of dynamic electrical breakdown of red sandstone to reproduce the generation of plasma channel, which can be mutually confirmed by indoor experimental results. The research results are essential for a deeper understanding of the rock breaking mechanism by electric pulse and for providing some theoretical guidance for the industrial application of electric pulse drilling technology.

The latest version of the SONIC code with the extended thermal force model that is capable to treat collisionality dependence of the force has been applied to the interpretative simulation of L-mode discharge of JT-60 U to investigate the impact of kinetic correction of the thermal force on the scrape-off layer (SOL) plasma properties. As a first attempt, we have selected an L-mode attached discharge #39090 (I_p = 1.6 MA, B_t = 3.1 T, and P_NBI = 4.5 MW), where $��{\bar{n}}_e�$ = 2.08 × 10¹⁹ m⁻³, $��{\bar{n}}_e�/�n_{\mathrm{Gr}}�$ = 0.392 with deuterium plasmas. It has been found that the peak values of SOL impurity density are reduced by a factor of 2, with the kinetic correction, because the thermal force is reduced by the low collisionality of SOL plasma between the X-point and the (inner and outer) midplane. On the other hand, the profiles near the divertor plates are unaffected by the kinetic correction due to the highly collisional condition. The kinetic correction is found more pronounced for the higher charge states impurity due to the charge dependence of the parallel impurity force balance. Overall effects due to the kinetic correction on the total impurity radiation and the divertor heat load are confirmed to be a few % in the present discharge condition of JT-60U.

The plasmon pole approximation used for the stopping function in a dense electron plasma is given a temperature-dependent cutoff wavenumber via the ion projectile thermal wavelength. Excepted for projectile inter-ion distance smaller than the target electron screening length and small ion fragment velocities, featuring a attosecond interaction time with a maximum correlated ion stopping (CIS) in inertial confinement fusion and warm dense matter (WDM), the given procedure is shown to yield back accurately the CIS estimated within the standard random phase approximation framework at any temperature, provided the ion fragment distribution is taken Gaussian.

This study investigates the diffusion of charged particles interacting through a Yukawa potential. Confined by a parabolic potential along the y-axis, the particles experience an aperiodic substrate potential along the x-axis. To analyze their diffusion behavior, we employ molecular dynamics simulations based on the Langevin equation. We primarily focus on the influence of particle density, system temperature, particle charge, and the aperiodicity parameter ($��L_2�$) of the quasi-aperiodic substrate on the system's diffusion characteristics. By adjusting $��L_2�$ for various system parameters, we can manipulate diffusion and observe diverse diffusion modes. Our findings reveal that the aperiodicity's effect becomes pronounced at lower densities and smaller $��L_2�$ values, leading to faster diffusion compared with the periodic case. However, over longer timescales, the system transitions to normal diffusion regardless of the specific parameters.

Discharge images under airflow, water level 150 mm, L = 40 mm, condition II (a) U = 10 kV, (b) U = 14 kV, (c) U = 18 kV. Fig. 4 of the paper by Desheng Zhou et al. https://doi.org/10.1002/ctpp.202300080

The effect of an ionic core on the temperature relaxation in dense hot plasma of beryllium is studied using the pseudpotential model by Gericke et al [Phys. Rev. E 2010, 81, 065401(R)]. Employing the screened version of the ion pseudpotential [by Ramazanov et al, Phys. Plasmas 2021, 28 (9), 092702], we computed the quantum transport cross section for the electron-ion collisions in dense beryllium plasma, where screening is taking into account using the density response function in the long-wavelength regime. The results for the transport cross section are used to compute a generalised Coulomb logarithm and electron-ion collision frequency. Utilizing the latter, we show the effect of the ionic core on the temperature relaxation. To understand the role of the ionic core, we compare the results with the data computed considering ions as point-like charges.

The modulation of surface properties of Ti₃C₂T_x plays a crucial role in its diverse applications across various fields. However, a straightforward and reliable technique for controlling its surface functional groups remains elusive. In this study, we achieved controlled modification of Ti₃C₂T_x surface functional groups using atmospheric-pressure cold plasma. We evaluated the plasma generation characteristics and found that the gas parameters could influence the discharge power and lead to different gas temperatures with the same voltage. Spectral analysis confirmed the presence of numerous reactive species in the plasma, facilitating the breaking and recombination of chemical bonds of functional groups on the Ti₃C₂T_x surface. The interaction between the plasma jet and Ti₃C₂T_x film revealed that the semiconductor properties of the Ti₃C₂T_x film limit the plasma diffusion area, while N₂ doping and increased gas flow rates respectively reduce and enlarge the coverage area of cold plasma. A brief one-minute cold plasma treatment induced a slight etching effect on the Ti₃C₂T_x film surface, effectively altering the -O and -F functional groups. However, it is noteworthy that excessive cold plasma treatment in the air may result in partial oxidation of Ti₃C₂T_x, necessitating the use of custom gas environments in further applications. This research provides valuable insights into surface modification techniques for Ti₃C₂T_x with potential implications in a wide range of applications.