Contributions to Plasma Physics最新文献

This paper presents the multi-species global impurity transport capability developed in a GPU-accelerated fully 3D unstructured mesh-based code, GITRm, to simultaneously track multiple impurity species and handle interactions of these impurities with mixed-material surfaces. Different computational approaches to model particle-surface interaction or surface response have been developed and compared. Sheath electric field is taken into account by employing a fast distance-to-boundary calculation, which is carried out in parallel on distributed or partitioned meshes on multiple GPUs without the need for any inter-process communication during the simulation. Several example cases, including two for the DIII-D tokamak, that is, one with the SAS-V divertor and the other with the collector probes, are used to demonstrate the utility of the current multi-species capability. For the DIII-D probe case, the capability of GITRm to resolve the spatial distribution of particles in localized regions, such as diagnostic probes, within non-axisymmetric tokamak geometries is demonstrated. These simulations involve up to 320 million particles and utilize up to 48 GPUs.

In this study, we developed a model to explore the characteristics of a magnetized plasma sheath, containing positive ions, electrons, and neutral particles. The ions are described using a fluid model based on the continuity and momentum equations, while the electron distribution is analyzed using three cases: the Maxwell–Boltzmann distribution and the Tsallis distribution in both 1-D and 3-D velocity spaces. Applying the Sagdeev method, we established the modified Bohm sheath criterion to obtain the required ion velocity at the sheath entrance for all three cases. The lower Mach number limit for Bohm velocity modification depends on factors such as ion temperature, ionization frequency, collision frequency, magnetic field angle, nonextensive parameter $��q�$, and the velocity space governing the density of nonextensive electrons, independent of magnetic field magnitude. Additionally, the electron velocity distribution was analyzed for various q-values, revealing that in 3-D velocity space, the energy range is broad and extensive, while in 1-D velocity spaces, it is narrower and confined within the broader 3-D interval. We examined the influence of key parameters on sheath characteristics under the Maxwellian distribution, as well as in 1-D and 3-D velocity spaces for the Tsallis distribution. The results demonstrated significant differences between the three cases, showing that in the 3-D case, the sheath thickness expands more compared to the 1-D and the Maxwell–Boltzmann distribution. This underscores the significance of accounting for the dimensionality of velocity space when investigating plasma sheath phenomena. Such understanding is crucial for optimizing plasma-surface interactions in various applications.

Particle-in-cell simulations of bilateral ion extraction process are carried out for electron focusing heating phenomenon in this work. The mechanisms and characteristics of the negative heating effect are simulated and analyzed. Then influences of several factors on electron heating degree and ion collection ratio are provided numerically. Finally, relations between the negative heating effect and extraction instability phenomenon are discussed and an approach to mitigate the heating effect is given.

A coupled electrothermal damage theory model for pipelines is proposed to assess the failure behavior of buried pipelines under lightning strikes. This article considers local thermal nonequilibrium (LTNE) conditions in the soil–water porous medium and the nonlinear characteristics of lightning functions. The calculation results show that the proposed theoretical model has better applicability and accuracy compared with previous models. Parametric analysis shows that under lightning conditions of I_m = 20 kA and T₁/T₂ = 1.2/50 μs, the maximum local temperature of the soil around the pipeline can reach 2160 K, leading to pipeline breakdown. Metal pipelines are shown to be more effective in conducting charges, which alters the electric field distribution in the soil and impacts the formation of plasma channels. The half-peak value of the lightning waveform has a significant impact on pipeline breakdown, and its increase will increase the risk of pipeline breakdown gradually. When considering LTNE conditions, the change in the pipeline surface temperature becomes more pronounced. Under 8/30 and 8/40 μs lightning waveforms, the pipeline surface temperature is approximately 150 and 550 K higher, respectively, compared with the thermal equilibrium conditions. The thermal conductivity and porosity of backfill soil can also affect the thermal damage of lightning-struck pipelines. With clay filling, the highest pipeline surface temperature can reach 2590 K, while with fine sand and coarse sand, it is 1980 and 1510 K, respectively. The pipeline lightning disaster model proposed in this article has engineering significance for the investigation of pipeline lightning failure and disaster prevention mechanisms.