Search

The detection of water molecules within the atmosphere of Jupiter, first by the Galileo Atmospheric Probe, and later by the Juno spacecraft, has given rise to the question of whether those molecules are sourced endogenously or exogenously. One hypothesis is that the ablation of meteoroids deposited the necessary oxygen into the atmosphere, which was subsequently used in chemical processes to form water. This paper aims to evaluate this hypothesis by simulating the ablation of carbonaceous objects entering the planet's atmosphere to determine the possible rates of oxygen delivery and the most likely altitude for such delivery within the Jovian atmosphere. We estimate that carbonaceous meteoroids have the potential to deliver $\sim 1.4 \times 10^7 \, \text{kg/m}^2$ of oxygen over a billion years. We further estimate that most of the ablation is expected to occur in the stratosphere, or 450-400 km above the region of 1 bar of atmospheric pressure. In comparison, Interplanetary Dust Particles (IDPs) are estimated to deliver roughly $\sim 10^2 \, \text{kg/m}^2$ of oxygen over the same period.

Plasma shape is a significant factor that must be considered for any Fusion Pilot Plant (FPP) as it has significant consequences for plasma stability and core confinement. A new simulator, NSFsim, has been developed based on a historically successful code, DINA, offering tools to simulate both transport and plasma shape. Specifically, NSFsim is a free boundary equilibrium and transport solver and has been configured to match the properties of the DIII-D tokamak. This paper is focused on validating the Grad-Shafranov (GS) solver of NSFsim by analyzing its ability to recreate the plasma shape, the poloidal flux distribution, and the measurements of the simulated diagnostic signals originating from flux loops and magnetic probes in DIII-D. Five different plasma shapes are simulated to show the robustness of NSFsim to different plasma conditions; these shapes are Lower Single Null (LSN), Upper Single Null (USN), Double Null (DN), Inner Wall Limited (IWL), and Negative Triangularity (NT). The NSFsim results are compared against real measured signals, magnetic profile fits from EFIT, and another plasma equilibrium simulator, GSevolve. EFIT reconstructions of shots are readily available at DIII-D, but GSevolve was manually ran by us to provide simulation data to compare against., Comment: 12 pages, 7 figures

This paper investigates energetic electron transport in magnetized toroidal plasmas with magnetic fields characterized by island chains and regions of stochastic field lines produced by coil perturbations. We report on experiments performed in the DIII-D tokamak, which utilize electron cyclotron heating and current drive pulses to tag electron populations within different locations across the discharge. The cross-field transport of these populations is then inferred from electron cyclotron emission measurements and gamma emission signals from scintillator detectors. Two types of energetic particles are distinguished and discussed: nonrelativistic suprathermal electrons and relativistic runaway electrons. The magnetic field topology in each discharge is reconstructed with field line tracing codes, which are also used to determine the location and scale of magnetic islands and stochastic regions. Comparison of simulations and experiments suggests that suprathermal transport is suppressed when the tagging is performed at a smaller radial location than the location of the q=1 island chain, and enhanced otherwise. We further demonstrate that increasing the width of the stochastic region within the edge plasma yields enhancement of the suprathermal electron transport.

We report on a study of the structure of edge turbulence in NSTX H-mode discharges with applied n=1 and n=3 non-axisymmetric magnetic perturbations. The edge turbulence is diagnosed in NSTX using the gas puff imaging (GPI) system to understand how these 3D fields affect edge transport. The presented database study uses a selection of discharges that have a change in the RWM coil current during the GPI gas puff. We compare the turbulence before and after this change in the applied non-axisymmetric fields, and compares the turbulence between the two states. Our findings show that these 3D fields do not have a strong, statistically significant impact on the average poloidal size, autocorrelation time, or relative fluctuation levels of the turbulence. In addition, we find that the displacement of the radial location of the GPI signal peak intensity is correlated with the shift in the perturbed separatrix location as predicted by the 3D vacuum magnetic field code MAFOT. We find that in general the non-axisymmetric fields from the RWM coils locally displace the edge flux surface as expected even when the self-consistent plasma response is not included, and that the model reproduces the localized shift observed by GPI.

Most methods for automated full-bore rock core image analysis (description, colour, properties distribution, etc.) are based on separate core column analyses. The core is usually imaged in a box because of the significant amount of time taken to get an image for each core column. The work presents an innovative method and algorithm for core columns extraction from core boxes. The conditions for core boxes imaging may differ tremendously. Such differences are disastrous for machine learning algorithms which need a large dataset describing all possible data variations. Still, such images have some standard features - a box and core. Thus, we can emulate different environments with a unique augmentation described in this work. It is called template-like augmentation (TLA). The method is described and tested on various environments, and results are compared on an algorithm trained on both 'traditional' data and a mix of traditional and TLA data. The algorithm trained with TLA data provides better metrics and can detect core on most new images, unlike the algorithm trained on data without TLA. The algorithm for core column extraction implemented in an automated core description system speeds up the core box processing by a factor of 20., Comment: 20 pages, 16 figures, 1 table, the augmentation pipeline code samples published as Open-Source code for TLA at https://github.com/BEEugene/TemplateArtification/, continue of the research from arXiv:1909.10227

We present the design of ATJ graphite rods developed for ablation experiments under high heat flux (up to 50 MW/m2) in the lower divertor of the DIII-D tokamak [1], a magnetic plasma confinement device. This work is motivated by the need to test ablation models relevant to carbon-based thermal shields used in high-speed spacecraft atmospheric entries, where the heat fluxes encountered can be comparable to those achieved in the DIII-D divertor plasma. Several different designs for the flow-facing side of the rod are analyzed, including "sharp nose," "blunt," and "concave". The last shape is studied for its potential to lower heat fluxes at the rod surface by increased radiation from trapped neutrals and reduced parallel plasma pressure. We also analyze the possibility of applying a thin (approximately 30 microns) layer of silicon carbide (SiC) to the exposed part of several carbon ablation rods to benchmark its erosion calculations and lifetime predictions. Such calculations are of interest as SiC represents a promising material for both thermal protection systems (TPS) and a fusion plasma-facing material (PFM). Preliminary results from the DIII-D rod ablation experiments are also discussed.

Edge-Localized-Mode (ELM) suppression by resonant magnetic perturbations (RMPs) generally occurs over very narrow ranges of the plasma current (or magnetic safety factor q95) in the DIII-D tokamak. However, wide q95 ranges of ELM suppression are needed for the safety and operational flexibility of ITER and future reactors. In DIII-D ITER Similar Shape (ISS) plasmas with n=3 RMPs, the range of q95 for ELM suppression is found to increase with decreasing electron density. Nonlinear two-fluid MHD simulations reproduce the observed q95 windows of ELM suppression and the dependence on plasma density, based on the conditions for resonant field penetration at the top of the pedestal. When the RMP amplitude is close to the threshold for resonant field penetration, only narrow isolated magnetic islands form near the top of the pedestal, leading to narrow q95 windows of ELM suppression. However, as the threshold for field penetration decreases with decreasing density, resonant field penetration can take place over a wider range of q95. For sufficiently low density (penetration threshold) multiple magnetic islands form near the top of the pedestal giving rise to continuous q95 windows of ELM suppression. The model predicts that wide q95 windows of ELM suppression can be achieved at substantially higher pedestal pressure in DIII-D by shifting to higher toroidal mode number (n=4) RMPs.

The description of rocks is one of the most time-consuming tasks in the everyday work of a geologist, especially when very accurate description is required. We here present a method that reduces the time needed for accurate description of rocks, enabling the geologist to work more efficiently. We describe the application of methods based on color distribution analysis and feature extraction. Then we focus on a new approach, used by us, which is based on convolutional neural networks. We used several well-known neural network architectures (AlexNet, VGG, GoogLeNet, ResNet) and made a comparison of their performance. The precision of the algorithms is up to 95% on the validation set with GoogLeNet architecture. The best of the proposed algorithms can describe 50 m of full-size core in one minute., Comment: 25 pages, 9 figures, 3 tables, submitted to Computers and Geosciences Journal. Keywords: Core Image; Description; Convolutional Neural Networks; Representation; Geology; Lithotypes