Determination of the characteristic magnetic pre-sheath length at divertor surfaces using micro-engineered targets on DiMES at DIII-D

The magnetic pre-sheath (MPS) width, L MPS, is a critical parameter to define the sheath potential, which controls the ion trajectory of low-Z species (D, T, He, and C), as well as the prompt re-deposition of high-Z species. To determine L MPS, we fabricated micro-trenches (30×30×4 µm) via focused ion beam (FIB) milling on a silicon surface and exposed them to L-mode deuterium plasmas in DIII-D via the Divertor Material Evaluation System (DiMES) removable sample exposure probe. The areal distribution of impurity depositions, mainly consisting of carbon, was measured by energy-dispersive X-ray spectroscopy (EDS) to reveal the deuterium ion shadowing effect on the trench floors. The carbon deposition profiles showed that the erosion was maximized for the azimuthal direction of φ = -40° (referenced to the toroidal magnetic field direction) as well as the polar angle of θ = 80°. A Monte Carlo equation-of-motion model, based on a collisionless MPS, was used to calculate the azimuthal and polar deuterium ion angle distributions (IADs) for a range of L MPS = k × ρ i, where ρ i is the ion gyro radius and k = 0.5-4. Then, gross erosion profiles were calculated by a Monte Carlo micro-patterning and roughness (MPR) code for ion sputtering using as input the calculated azimuthal and polar IADs for each value of k. Good agreement with the experimental C deposition profiles was obtained for the case k = 2.5-3.5. This result is consistent with a previous kinetic modeling prediction of k ~ 3, as well as previous analytical investigations that predicted the L MPS to be several ion gyro radii. A validation of theoretical sheath models supports its applicability to ITER and pilot plant divertors to successfully predict plasma-materials interactions.

BIOSTRATIGRAPHY AND SEQUENCE STRATIGRAPHY OF THE DEEP OFFSHORE NIGER DELTA AND IMPLICATIONS FOR FUTURE HYDROCARBON EXPLORATION IN THE PALAEOGENE SEQUENCES

The Niger Delta Deep Offshore Basin has been the latest frontier within the Niger Delta for hydrocarbon exploration and production activities. Until the onset of drilling activities in the early nineteen nineties, little was known about the biostratigraphy of this frontier setting. Thus, uncertainties existed in the ages ascribed to the various stratigraphic sequences. Presently, several wells have been drilled in the Deep Offshore Niger Delta and a three-pronged biostratigraphic data and some sequence stratigraphic interpretations have become available. We integrated biostratigraphic data comprising palynological, foraminiferal, and calcareous nannoplankton zonation and biofacies, wireline log information and regional-3D seismic data, with simple basic sequence stratigraphic analysis for a detailed well correlation, regional mapping of hydrocarbon-bearing intervals, and evaluation of the thicknesses of promising stratigraphic intervals. Results show a significant effect on not only the earlier conceptualized age of the deepest prospective reservoirs, but also the ages of possible source rocks in the Paleogene of the Niger Delta Offshore sequence. This finding will help in the realistic assumptions of source rock characterization, charge modeling/prediction, and the stratigraphic thicknesses of the offshore sequences and their reservoirs. This paper examines the specific derivable age interpretations from the integration of at least six wells, biostratigraphic data with seismic and the implications of these interpretations for hydrocarbon prospectivity of the Paleogene sequences. Furthermore, this paper documents the biostratigraphy work done in the area, in all the structural belts where drilling has occurred including the deepest well drilled in the Deep Offshore Niger Delta, Bosi-006. The results of this study have a critical impact on the current regional geological understanding of the Deep Offshore Niger Delta.

Influence of montane altitudinal ranges on species distribution models; evidence in Andean blow flies

Background Blow flies are a family of dipterans of medical, veterinary and sanitary importance. We aim to predict the current geographical distribution of six neotropical blowfly species with different altitudinal ranges of distribution (high, medium, and lowlands) and degree of synanthropy (eusynanthropic, hemisynanthropic and asynanthropic) based on their existing fundamental niche (EA) in Northwestern South America. Methods Geographical records were compiled based on data from museum specimens and literature. The accessible area hypothesis (M) was calculated based on three criteria: (1) Altitudinal range, (2) Synanthropy values deducted based on the Human Influence Index (HII) raster dataset, and (3). The mean dispersal capability of flies. The modeling was performed using the Maxent entropy modeling software. The selection of parameters was made with the R Program ENMeval package. Results The models were assessed using the area under the operator-partial receiver curve (ROCp). The high statistical performance was evidenced in every modeling prediction. The modeling allowed identifying possible taxonomic inaccuracies and the lack of exhaustive collection in the field, especially for lowlands species. Geographical distribution predicted by the modeling and empirical data was remarkably coherent in montane species. Discussion The data obtained evidence that montane elevational ranges affect the performance of the distribution models. These models will allow a more precise predicting of medium and high elevation blow flies than lowlands species. Montane species modeling will accurately predict the fly occurrence to use such biological information for medical, legal, veterinary, and conservation purposes.