Kinetic-MHD hybrid simulation of fishbone modes excited by fast ions on the experimental advanced superconducting tokamak (EAST)

Kinetic-MagnetoHydroDynamic hybrid simulations are carried out to investigate fishbone modes excited by fast ions on the Experimental Advanced Superconducting Tokamak. The simulations use realistic equilibrium reconstructed from experiment data with the constraint of the q = 1 surface location (q is the safety factor). Anisotropic slowing down distribution is used to model the distribution of the fast ions from neutral beam injection. The resonance condition is used to identify the interaction between the fishbone mode and the fast ions, which shows that the fishbone mode is simultaneously in resonance with the bounce motion of the trapped particles and the transit motion of the passing particles. Both the passing and trapped particles are important in destabilizing the fishbone mode. The simulations show that the mode frequency chirps down as the mode reaches the nonlinear stage, during which there is a substantial flattening of the perpendicular pressure of fast ions, compared with that of the parallel pressure. For passing particles, the resonance remains within the q = 1 surface, while, for trapped particles, the resonant location moves out radially during the nonlinear evolution. In addition, parameter scanning is performed to examine the dependence of the linear frequency and growth rate of fishbones on the pressure and injection velocity of fast ions

Simulations of toroidal Alfvén eigenmode excited by fast ions on the Experimental Advanced Superconducting Tokamak

Kinetic-MagnetoHydroDynamic (MHD) hybrid simulations are carried out to study fast ion driven toroidal Alfvén eigenmodes (TAEs) on the Experimental Advanced Superconducting Tokamak (EAST). The first part of this article presents the linear benchmark between two kinetic-MHD codes, namely MEGA and M3D-K, based on a realistic EAST equilibrium. Parameter scans show that the frequency and the growth rate of the TAE given by the two codes agree with each other. The second part of this article discusses the resonance interaction between the TAE and fast ions simulated by the MEGA code. The results show that the TAE exchanges energy with the co-current passing particles with the parallel velocity |ν| ≈ V a0/3 or |ν| ≈ V A0/5 where V A0is the Alfvén speed on the magnetic axis. The TAE destabilized by the counter-current passing ions is also analyzed and found to have a much smaller growth rate than the co-current ions driven TAE. One of the reasons for this is found to be that the overlapping region of the TAE spatial location and the counter-current ion orbits is narrow, and thus the wave-particle energy exchange is not efficient

A Deterministic Method for Evaluating Safety Factor of Deep Excavation Stability against Groundwater Inrush Equivalently Considering Soil Uncertainty

In current design specifications for deep excavation, the determination of safety factors against groundwater inrush only considers the self-weight effect of soil mass at the bottom. However, the shear strength and its spatial variability in a cement-solidified bottom layer also plays an important role in safety factor estimation. Based on that, in this study, the strength reduction method was introduced into reliability analysis of deep excavation engineering, and the influence of shear strength and its spatial variability of cement-solidified soil on the stability of deep excavation is studied. Furthermore, a deterministic analysis method that can equivalently consider soil uncertainty is proposed and verified

Health impacts of an extreme dust event: a case and risk assessment study on airborne bacteria in Beijing, China

Abstract Dust events are concerning due to their potential to cause environmental pollution and health issues by carrying numerous particles from various regions. However, the risks of airborne bacteria from dust have not yet been thoroughly investigated. This study aimed to reveal the particle size distribution, antibiotic resistance, microbial community structure, and diversity of airborne bacteria by using culture methods, and assess the potential health risks by calculating the dose expectation $$(\overline{d })$$ ( d ¯ ) , daily short-term intake (STI), and Hazard Index (HI) during an extreme dust event in urban Beijing (China). Airborne bacteria were sampled before, during, and the day after a severe dust event in March 2021 in Beijing using the six-stage impactor. The major findings were as follows: (1) airborne bacterial concentration increased during the dust event, and inhalable bacteria account for 67.93%. The Hazard Index (HI) of cultivable and inhalable airborne bacteria in men, women, and children exposed to dust events was up to 1.42 and 1.54 times higher than that in individuals who were not exposed, respectively. HI was 1.52 times higher in children than in men when exposed to the dust event. (2) The percentage of Gram-positive bacteria (GPB) resistant to different antibiotics was altered. The abundance of ciprofloxacin-resistant bacteria increased by 24.51%, while that of clindamycin-resistant bacteria decreased by 34.64%. The $$\overline{d }$$ d ¯ , STI, and HI of antibiotic-resistant bacteria per breath for men, women, and children after the dust event were 14 times greater than those before the dust event. (3) The diversity of airborne bacteria increased throughout the dust event. Opportunistic bacteria were found after the dust event. From a health perspective, airborne bacteria during extreme dust events should be further studied for their sources, changes, human exposure, and so forth. Government-scale measures are necessary to control dust dissemination. Graphical Abstrac