Investigating the n=1 and n=2 error fields in W7-X using the newly accelerated FIELDLINES code

No fusion device can be created without any uncertainty; there is always a slight deviation from the geometric specification. These deviations can add up create a deviation of the magnetic field. This deviation is known as the (magnetic) error field. Correcting these error fields is desired as they cause asymmetries in the divertor loads and can thus cause damage to the device if they grow too large. These error fields can be defined by their toroidal (n) and poloidal number (m). The correction of the n = 1 and n = 2 fields in Wendelstein 7-X (W7-X) is investigated in this work. This investigation focuses on field line diffusion to the divertor, a proxy for divertor heat flux. Such work leverages the 25x speedup obtained through the implementation of a new particle-wall collision model. The n = 1 and n = 2 error fields of the as-built coils model of W7-X are corrected by scanning phase and amplitude of the trim and control coils. Reductions in the divertor load asymmetry by factors of four are demonstrated using error field correction. It is found that the as-built coils model has a significantly lower m⁄n = 1⁄1 error field than found in experiments.

Placement of a fast ion loss detector array for neutral beam injected particles in Wendelstein 7-X

In light of measuring the fast ionized particle confinement in the stellarator Wendelstein 7-X, particles generated by the neutral beam injection system are simulated to determine the placement of an array of faraday-cup fast ion loss detectors. This array is important due to the localization of the loss pattern, which changes drastically with experimental parameters. The Monte Carlo codes BEAMS3D and ASCOT5 are used for the simulations, following the particles from injection to wall collision. Different magnetic configurations and plasma pressures are investigated in this manner, and a configuration suitable for measuring the loss fraction is found. It qualitatively reproduces the global losses, is installable in locations of current carbon wall-tiles and the individual detector output appears well-suited for experimental purposes.

Curvature flows, scaling laws and the geometry of attrition under impacts

Impact induced attrition processes are, beyond being essential models of industrial ore processing, broadly regarded as the key to decipher the provenance of sedimentary particles. Here we establish the first link between microscopic, particle-based models and the mean field theory for these processes. Based on realistic computer simulations of particle-wall collision sequences we first identify the well-known damage and fragmentation energy phases, then we show that the former is split into the abrasion phase with infinite sample lifetime (analogous to Sternberg’s Law) at finite asymptotic mass and the cleavage phase with finite sample lifetime, decreasing as a power law of the impact velocity (analogous to Basquin’s Law). This splitting establishes the link between mean field models (curvature-driven partial differential equations) and particle-based models: only in the abrasion phase does shape evolution emerging in the latter reproduce with startling accuracy the spatio-temporal patterns (two geometric phases) predicted by the former.

Numerical simulation of the particle-wall collision strength and swirling effect on the performance of the axial flow cyclone separator

The axial cyclone separator has simple structure, operates to reducing dust concentration in grain storehouses, and features low production cost, and convenient installation. Aiming to obtain the separation characteristics of an axial flow guide separator, the particle wall collision and the performance of multi-tubes were simulated with Fluent. The renormalization group (RNG) k − ε model was used to study the turbulent modeling and the user define function (UDF) was used to calculate the particle-wall collision. The simulation and experimental results were compared to verify the computation model. The results showed that the basic feature of the flow pattern remains stable and the separation efficiency of 800 kg/m3 particles is higher than 2650 kg/m3 particles when the inlet velocity increases from 2 to 5 m/s. When the inlet velocity was 5 m/s, the normal velocity restitution ratio had a significant effect on the efficiency, the separation efficiency of 167 μm particles changed from 76.74 to 97.93% and a smaller normal velocity restitution ratio had a higher the efficiency. In comparison, the efficiency remained unchanged when changing the tangential velocity restitution ratio. Furthermore, the effects of three target wall materials on the separation efficiency were investigated. And the simulated efficiency the of 296 μm particle of 2024 aluminum, 410 stainless steel and Ga1–4V titanium were 82.15, 79.52 and 77.53% respectively. Besides, effects of tube diameter on performances of cyclone separator were discussed and high intense collisions between particles and walls may occur in a small diameter of cyclone tube, causing deteriorated separation performance. Moreover, with the addition of the dust chamber, the efficiency of cyclone used in combination is slightly improved since the vortex in the exhaust pipe has been finely changed.

Collision Avoidance and Stability Study of a Self-Reconfigurable Drainage Robot

The inspection and maintenance of drains with varying heights necessitates a drain mapping robot with trained labour to maintain community hygiene and prevent the spread of diseases. For adapting to level changes and navigating in the narrow confined environments of drains, we developed a self-configurable hybrid robot, named Tarantula-II. The platform is a quadruped robot with hybrid locomotion and the ability to reconfigure to achieve variable height and width. It has four legs, and each leg is made of linear actuators and modular rolling wheel mechanisms with bi-directional movement. The platform has a fuzzy logic system for collision avoidance of the side wall in the drain environment. During level shifting, the platform achieves stability by using the pitch angle as the feedback from the inertial measuring unit (IMU) mounted on the platform. This feedback helps to adjust the accurate height of the platform. In this paper, we describe the detailed mechanical design and system architecture, kinematic models, control architecture, and stability of the platform. We deployed the platform both in a lab setting and in a real-time drain environment to demonstrate the wall collision avoidance, stability, and level shifting capabilities of the platform.