Contributions to Plasma Physics最新文献

This paper studies the acceleration of an electron in a magnetized plasma waveguide caused by the interaction between the twisted electromagnetic wave and the plasma wave in a motional plasma. The spatial dependence of the amplitude and phase of the twisted TM mode has been derived by solving the wave equation. With appropriately assigned initial values, total electron energy gain can be calculated using numerical calculations. Numerical results show that plasma motion, as long as the twisted electromagnetic wave pulse, significantly affects electron acceleration during an electron's passage through the waveguide.

Only recently, plasma edge simulations up to the wall have been enabled with SOLPS-ITER. This requires dedicated gridding techniques to reconcile grid alignment with the magnetic field and refinement toward the wall as grid quality is primordial to ensure fast and reliable convergence. Therefore, the gridding approach for the grids up to the wall is analyzed and improved. A truncation error analysis is performed on the discrete operators of the discretization scheme in SOLPS-ITER, resulting in indicators of grid properties that are undesired. Based on these indicators, grid adaptation and grid smoothing algorithms are developed to reduce truncation errors and improve the overall grid quality. The resulting methods are applied on an AUG single-null case. Here, the impact of the new gridding strategy is examined on the divertor heat load, a typical quantity of interest for plasma edge simulations. The new gridding methods allow to mitigate spurious numerical spikes in the target heat load profiles, reduce the convergence time with a factor 30, and improve the accuracy of the heat load with a factor 3 compared to original grids with similar total number of cells.

The effect of differential biasing of the divertor plates in a tokamak is analyzed using SOLPS-ITER modeling with account of drifts and currents in the SOL. The ASDEX-Upgrade like geometry and transport parameters adjusted for modeling of the semi-detached nitrogen-seeded plasma of shot #28903 are used in analysis. The additional voltage is applied to the outer divertor plate with respect to the grounded vacuum chamber and the inner divertor plate. When high negative voltage is applied, the high field side high density region almost disappears and the divertor plates become more symmetrical than without biasing, while in the case with positive voltage, the formation of the X-point radiator begins, and both divertor plates become more detached. The results are qualitatively consistent with the experiments conducted on the JFT-2 M and DIII-D tokamaks. In addition, both signs of the applied voltage lead to a significant redistribution of the nitrogen within the SOL. Therefore, the possibility of edge plasma control by biasing is demonstrated.

This study investigates the counterintuitive behaviors of a microwave-induced atmospheric pressure plasma jet (APPJ) under the influence of an external electrostatic field applied by one or a pair of parallel electrode plates subjected to DC voltages. The findings demonstrate that the plasma jet consistently deflects toward the electrode plate with an electrostatic potential, irrespective of the direction of the applied field. The deflection becomes more pronounced with increasing voltage on the electrode plate until the ionic wind generated by the high voltage significantly affects the jet's behavior. Remarkably, a negative voltage induces a greater deflection compared to a positive voltage. To further investigate this discovery, the dielectric properties and the non-neutral characteristics of the APPJ are analyzed, and the simulations of the electric field distribution reveal a non-uniform distribution, which plays a crucial role in understanding the mechanism behind the observed behaviors of the plasma jet. This study provides a comprehensive understanding of the underlying mechanism driving the observed phenomena and sheds light on the collective behavior of plasma jets under non-uniform electric fields. The findings of this study offer valuable guidelines for investigating and controlling the behavior of APPJs.

Distribution of internal plasma channel temperature and rock conductivity under different magnetic field conditions. Fig. 9 of the paper by Weiji Liu et al., https://doi.org/10.1002/ctpp.202300086

The magnetic topology is a critical issue in fusion plasma research. An example is the Resonant Magnetic Perturbation (RMP), which controls the edge transport in tokamaks. However, the physics of how the RMP affects edge transport is not clear. One reason is the transport process on the stochastic magnetic field is poorly understood. This study examines anisotropic heat diffusion numerically to understand heat transport in stochastic magnetic fields. We developed a numerical model of an anisotropic temperature diffusion model, where the significant deviation of the parallel and perpendicular thermal conductivity exists. We applied this implementation to the realistic stellarator geometry with the stochastic magnetic field in the edge. The smooth temperature profile is obtained for the large perpendicular diffusion, although the magnetic field is stochastic. However, for another case of significant parallel diffusion, the small flattening of the temperature on the magnetic island in the stochastic region appears. That result suggests that the stochastic magnetic field can keep the finite temperature gradient if the connection length of the magnetic field line in the stochastic region is sufficiently long.

The burst of edge-localized modes (ELMs) leads to an increase in the energy and particle fluxes to the divertor target. Tungsten (W) is chosen as the primary candidate material for plasma-facing components (PFCs) in the future fusion devices, and EAST has already upgraded all divertors to use W. Therefore, understanding tungsten target erosion during ELMs and finding the correlation between erosion rate and key ELM parameters are crucial for steady-state operation. In this work, based on the Vlasov–Poisson model (VPM), we develop a one-dimensional kinetic parallel transport code to investigate the parallel transport of particles in the EAST device during ELMs and the resulting target erosion. The EAST experiment (#102182) is simulated by VPM code. The simulation results are compared with experimental data as well as free-stream model (FSM) calculation, showing the accuracy of the code. Considering the presence of lithium (Li) impurities in EAST discharge, the erosion of the W target is simulated. The results indicate that during the burst of ELM, the total average tungsten erosion rate, $��{\Gamma }_{\text{total}}^{\mathrm{AVG}}�$, is determined by both deuterium (D) and Li ions. D ions dominate the erosion when the ELM frequency (f_ELM) is low (ranging from 50 to 175 Hz), while Li impurities become more important than D⁺ in high-frequency ELMs (f_ELM > 175 Hz). As f_ELM increases, the time-averaged erosion of the W target first increases and then decreases. Therefore, the reduction of W erosion benefits from high-frequency ELMs, with impurity ions being the primary contributor to the erosion.

A linear plasma device (LPD) module has been developed under the BOUT++ framework to simulate plasma transport in the MPS-LD. However, previously, the LPD module used a simplistic neutral particle model that only includes particle density and velocity, which prevents the full understanding of the plasma-neutrals interactions. In this work, we further optimize the neutral model by using a more complete neutral fluid model containing the continuity equation, momentum equation, and energy equation. The reactions such as charge exchange, excitation, and radiation collisions are included. Since the neutral particle source is mainly provided by particle recycling from the target, a particle recycling model is employed, which includes both fast reflection and slow thermal release. The upgraded LPD module is applied to simulate the argon (Ar) discharge experiment of MPS-LD, and the benchmark against experiment measurement and SOLPS-ITER simulation results are presented. Good agreements are obtained, showing the validation of the upgraded module. After that, the impact of particle recycling on Ar plasma is investigated. It is found that a higher recycling coefficient (R) promotes the achievement of high-density plasma at the target. The recycled Ar atoms change target plasma pressure as well as plasma-neutral collisions, which both contribute to plasma momentum loss, thus promoting the rollover of ion flux to the target.

Efficient handling of high heat flux on the plasma-facing components, particularly the divertor targets, poses a significant challenge for the Chinese Fusion Engineering Testing Reactor (CFETR) with fusion power of Gigawatt. This work investigates the divertor plasma detachment of CFETR with a standard ITER-like divertor geometry by neon (Ne) or argon (Ar) impurity seeding using UEDGE code. The cross-field drifts terms are switched off, and fluid neutral models and a “fixed-fraction” impurity model are applied to enable efficient simulations for the study of CFETR detachment. In order to reduce the heat load on the divertor targets below the acceptable level (<10 MW/m²), the impurity fraction (f), pumping speed (S), and upstream density are varied to identify the suitable operations window during Ne seeding. The effects of Ne and Ar impurities on the plasma detachment are compared. It is found that with the power across the core-edge interface P_SOL = 200 MW and separatrix density of 2.8 $��\times �$ 10¹⁹ $��m^{�-�3�}�$, Ne impurity fraction ≥1.7%, and Ar impurity fraction ≥0.24% can achieve the partial detachment. Achieving similar total radiation power (˜148 MW), the Ne fraction is 2.3% and the Ar fraction is 0.24%. Moreover, the simulation results indicate that Ar exhibits better power radiation efficiency and core compatibility compared with Ne.