Contributions to Plasma Physics最新文献

Crystallization of dense matter in neutron star crusts and white dwarf cores may be similar to epitaxial crystal growth in terrestrial laboratories. However, in stellar crystals, the spacing between horizontal planes has to gradually increase with the outward movement of the crystallization front, tracing decrease of the electron density. This process produces Coulomb crystals with stretched rather than cubic elementary cells. We extend the analysis of the elastic and breaking properties of such crystals to the face-centered (fc) lattice. Shear deformations orthogonal to the stretch direction have been studied for 22 crystallographic shear planes. A common property for all these planes is the reduction and eventual nulling of the breaking shear strain with deviation from the unstretched configuration. The effective shear moduli for deformations orthogonal to the stretch direction have been calculated. It is possible that the epitaxial crystallization in compact stars results in a formation of large-scale crystallites or, at least, in growth of the whole crystallization front perpendicular to particular crystallographic planes. For fc structure growth orthogonal to the $���\left\{�111�\right\}��$ planes, we expect that, at any density, $��\sim �5�\%�$ ($��\sim �0.5�\%�$) of crystallite height is occupied by layers one (two) orders of magnitude weaker than the bulk of the crystallite. This may be important for realistic modeling of crustquakes on neutron stars.

Yuri L'vovich Klimontovich (September 28, 1924–October 26, 2002) was an outstanding theoretical physicist who made major contributions to kinetic theory. On the occasion of his 100th birthday, we recall his main scientific achievements.

This paper presents a first implementation of gradient, divergence, and particle tracing schemes for the EMC3 code, a stochastic 3D plasma fluid code widely employed for edge plasma and impurity transport modeling in tokamaks and stellarators. These schemes are essential to accommodate plasma drift computations, which are currently absent in the code. Plasma drifts have been recognized to significantly influence transport of particles and energy, and their inclusion in future code upgrades will substantially enhance the code's predictive capabilities. For gradient and divergence calculations, we introduce a second-order least-squares gradient scheme. We confirm the second-order convergence properties and assess the accuracy of several analytical test cases in the presence of synthetic noise. In the second part of this paper, we employ the validated gradient scheme in a fourth-order Runge–Kutta particle tracing scheme to trace a particle through a generic drift velocity field. The impact of synthetic noise on the scheme's performance is investigated by evaluating various error metrics. We find that the implemented schemes function as intended and exhibit sufficient accuracy to enable drift computations.

A Pulsed ns laser operating at 532 nm wavelength with 150 mJ pulse energy was employed to irradiate micrometric thick mylar films, from 1 to 100 μm thick, covered by 0.05 μm Au in the back face. Protons and light ions have been accelerated by the electric field developed in the non-equilibrium plasma by the laser pulse in a vacuum at an intensity of the order of 10¹⁰ W/cm². Time-of-flight technique, obtained using a Faraday cup and a fast storage oscilloscope, is employed to measure the ion velocity, energy, and yield emitted in backward and forward directions. The yield of the emitted plasma photons is also evaluated. Two ion collectors are used in opposite directions to measure the plasma radiations emitted in backward and forward directions. Data analysis is based on the Coulomb-Boltzmann-shifted (CBS) distribution function. The target ablation yield is evaluated in the order of 3.5 μm per laser shot.

Based on High Magnetic field Helicon eXperiment, considering the parabolic distribution and Gaussian distribution of radial plasma density, HELIC code was used to study the influence of temperature and pressure gradient on power deposition, electric field, and current density of Helicon Wave Plasma. Three different gradients (positive, negative, and zero gradient) were selected. The results show that positive temperature gradient is beneficial to increase the relative absorption power at the center of plasma. Compared with negative and zero pressure gradients, positive pressure gradient increases the relative absorption power and weakens the current density at the center of plasma, and increases the electric field intensity at the edge of plasma. Larger edge heating will cause the relative absorption power at edge to rise rapidly, which is not conducive to the coupling at the center of plasma. In practical experiments, it is particularly important to reduce the heating effect at edge by cooling the antenna itself. Three different gradients of temperature and pressure have little effect on electric field intensity and current density in plasma, and the variation trend is basically similar, which proves the stability of the antenna mode: m = 1.

The trajectories and the ablation positions of boron dust particles dropped from an impurity powder dropper in the peripheral plasma in the Large Helical Device (LHD) were calculated using a three-dimensional edge plasma simulation code (EMC3-EIRENE) and a dust transport simulation code (DUSTT). The simulation shows that the trajectory of the boron dust particles is deflected at the upper divertor leg due to the effect of the hydrogen plasma flow, and the ablation positions of the dust particles in an ergodic layer change toward the outboard side of the torus for higher plasma densities. The effect of the boron ion flow in the divertor leg on the deflection is investigated by coupling the two codes self-consistently. The simulation predicts that the boron ions in the divertor leg, which are produced by sputtering on the divertor plates, which do not affect the change in the ablation positions. It also shows that the ablation positions move toward the inboard side and approach the Last Closed Flux Surface (LCFS) in case of increased boron dust drop rates, which is caused by the lowered plasma flow in the upper divertor leg due to the lowered electron temperature by radiation cooling by the dropped dust particles.

In this study, we investigate the dependence of potential energy of the one–component plasma on the number of particles with pure Coulomb, Ewald, and angular–averaged Ewald potentials. We show that in the weakly–coupled regime, the Coulomb potential provides a faster convergence of the energy to the thermodynamic limit. However, in the medium- and, especially, strong-coupling regime, the Ewald potential shows significantly better convergence. Thus, the criticism of the Ewald potential in [Fraser et al. Phys. Rev. B 53, 1814 (1996)] within classical simulations turns out to be unjustified in this case: the accounting for long-range interaction effects greatly improves the $��N�$-convergence of one–component plasma thermodynamic functions.

Experimental results from several tokamaks suggest a strong impact of divertor density regimes on turbulent transport in the edge plasma. Reciprocally, the change in transverse transport and SOL width affects the access to density regimes, making it a fundamental topic for heat exhaust issue. Such phenomenology is highly nonlinear and can only be approached quantitatively using numerical simulations treating turbulence and neutrals recycling physics self-consistently. In this study, the SOLEDGE3X edge multi-fluid code is used to investigate the mutual interaction between edge plasma turbulence and neutrals recycling. A fluid neutrals model based on the assumption of a charge-exchange-dominated plasma-neutral interaction has been implemented. Two simulations in circular geometry are compared: one without neutrals, where the particle flux is driven by a constant in flux from the core region, and the other one with neutrals recycling included in which the particle input to the system is self-consistently injected by a gas puff from the midplane. The presence of the neutrals triggers three types of perturbations on the plasma: a local and non-axisymmetric one driven by the gas puff, a global perturbation affecting both profiles and turbulence properties in the whole domain, and a local one in the vicinity of the limiter where recycling occurs. The largest effect of the inclusion of self-consistent neutrals recycling is a large-scale reorganization of the plasma profiles and turbulence properties due to the dissociation of particle and energy fluxes. These effects are expected to be more important at higher densities regimes or in diverted configuration.

Charging and dynamics of a spherical dust grain injected into a continuous and pulsed radio frequency (RF) discharge have been studied using a one-dimensional fluid model. First, the plasma characteristics of the two types of discharges are computed and compared. In the pulsed discharge, it is found that the central electron density exhibits a periodic variation while the averaged electron density is lower compared to that in the continuous discharge due to the decrease in the total ionization rate. Further, the dust charge is computed using the plasma characteristics. It is found that the dust charge negatively increases as the duty cycle ratio increases. Also, the charge in the pulsed discharge is lower in comparison to the continuous discharge due to the shorter duration of the pulsed RF discharge limiting the amount of energy transferred to electrons. On the other hand, the dust particle remains in the powered sheath region exhibiting a damped oscillation in the two discharges with higher oscillation frequency in the continuous discharge.

Tungsten (W) impurity eroded from the divertor target can degrade the confinement performance of future fusion reactors. The mechanism of the effect of E × B drift on the W transport in the scrape-off layer (SOL) was investigated with a fixed cross-field anomalous particle diffusion coefficient for W ions (D_⊥,W) of 1 m²s⁻¹ in our previous simulation work, which indicates that the W flux entering the confined region (Γ_enter) and mean W concentration in the confined region ($��C_W^{\mathrm{avg}}�$) can be increased by more than one order of magnitude by drifts. In this work, the influence of the cross-field anomalous diffusion on the W transport in the SOL is further investigated. The basic flow pattern of the W ion flux (Γ_W) keeps when D_⊥,W varying from 0.5 to 3 m²s⁻¹, and Γ_enter mainly comes from the hotter divertor region. Results show that D_⊥,W value affects the W leakage from divertor region and entry into confined region. Therefore, Γ_enter and $��C_W^{\mathrm{avg}}�$ both decrease with increasing D_⊥,W. Mechanisms for cases w/wo drifts are compared.