DETERMINATION OF NEAR-SOL CARBON IMPURITY CONTENT DUE TO DIVERTOR TARGET LEAKAGE USING CARBON-13 TRACERS VIA METHANE INJECTION ON THE DIII-D TOKAMAK

Experiments with outer strike point injection of isotopically enriched methane (13CD­4) in DIII-D L-mode discharges have demonstrated the ability to infer near scrape-off-layer (SOL) impurity density profiles based on: far-SOL collector probe (CP) measurements; a stable isotopic mixing model; and SOL impurity transport modelling. This work enables one of the first in-depth investigations on the source and transport of SOL impurities which could hinder performance of future fusion devices. Modelling by DIVIMP and 3DLIM of 13C SOL evolution is consistent with diagnostic observations and indicates that the buildup of injected impurities on plasma-facing surfaces must be considered while inferring representative impurity distributions. Namely, 13C deposits on the inner and outer targets are shown to contribute 50% at a minimum of the enriched 13C deposition on CPs and to cause poloidal shifting of the impurity density peaks in the near-SOL. This analysis elucidates the importance of source location, connection length, poloidal diffusion, and radial convective velocity of impurities to accurately model and interpret SOL impurity behavior

The Application of Mass Spectrometry Techniques for the Benefit of Tungsten Impurity Transport Research and Nuclear Fusion

Several barriers prevent the capability of on the grid nuclear fusion power plants. With the research presented here, these issues are confronted and the work makes progress towards addressing known gaps in the fusion community’s understanding of material and impurity migration in fusion devices. Recent successes that were achieved during the DIII-D metal rings campaign of the summer in 2016 must continue to develop in preparation for testing on additional plasma devices. During this campaign, impurities generated from the metal tiles of DIII-D were collected on graphite collector probes. These were then studied with several techniques, and it has been shown that traditional analytical techniques such as Rutherford backscattering and inductively coupled plasma mass spectrometry (ICP-MS) are able to determine the presence and isotopic ratios of heavy metals. Adding to these tools, an in depth study of laser ablation mass spectrometry (LAMS) is necessary. Methods have been developed so that they may be used in direct solid sample analysis of graphite collector probes using LAMS. With these procedures in place, a comparative study has be completed between the LAMS system and traditional aqueous intake ICP-MS. With these results in hand, empirical evidence may be used to benchmark computational techniques for interpretive modeling of impurity transport in fusion devices like the DIVIMP-OEDGE-WallDYN code

Phaseless computational imaging with a radiating metasurface

Computational imaging modalities support a simplification of the active architectures required in an imaging system and these approaches have been validated across the electromagnetic spectrum. Recent implementations have utilized pseudo-orthogonal radiation patterns to illuminate an object of interest---notably, frequency-diverse metasurfaces have been exploited as fast and low-cost alternative to conventional coherent imaging systems. However, accurately measuring the complex-valued signals in the frequency domain can be burdensome, particularly for sub-centimeter wavelengths. Here, computational imaging is studied under the relaxed constraint of intensity-only measurements. A novel 3D imaging system is conceived based on 'phaseless' and compressed measurements, with benefits from recent advances in the field of phase retrieval. In this paper, the methodology associated with this novel principle is described, studied, and experimentally demonstrated in the microwave range. A comparison of the estimated images from both complex valued and phaseless measurements are presented, verifying the fidelity of phaseless computational imaging.Comment: 18 pages, 18 figures, articl

A Study of Social Security Disability Litigation in the Federal Courts

A person who has sought and failed to obtain disability benefits from the Social Security Administration (“the agency”) can appeal the agency’s decision to a federal district court. In 2015, nearly 20,000 such appeals were filed, comprising a significant part of the federal courts’ civil docket. Even though claims pass through multiple layers of internal agency review, many of them return from the federal courts for even more adjudication. Also, a claimant’s experience in the federal courts differs considerably from district to district around the country. District judges in Brooklyn decide these cases pursuant to one set of procedural rules and have in recent years remanded about seventy percent to the agency. Magistrate judges in Little Rock handle this docket with a different set of rules and have in recent years remanded only twenty percent. The adjudication of disability claims within the agency has received relentless attention from Congress, government inspectors general, academic commentators, and others. Social security litigation in the federal courts has not weathered the same scrutiny. This report, prepared for the Administrative Conference of the United States, fills this gap. It provides a comprehensive qualitative and quantitative empirical study of social security disability benefits litigation. Our report makes four contributions. The first is a thorough introduction to the process by which a disability benefits claim proceeds from initial filing to a federal judge’s chambers. This description is intended to deepen understandings of where many of federal civil cases come from, and why they raise the same sorts of concerns repeatedly. Second, the report provides some context for understanding why the federal courts remand claims to the agency at the rate that they do. We argue that the federal courts and the agency have different institutional goals, commitments, and resources. These differences would cause a sizable number of remands even if the agency adjudicated claims successfully and the federal courts applied the appropriate standard of review. Third, we undertake extensive statistical analysis to try to understand what factors explain the sharp variation in district-level remand rates. Circuit boundaries account for some, but not all, of this disparity. After excluding a number of other potential causes, we hypothesize that district courts remand claims to the agency at different rates in part because uneven adjudication within the agency produces pools of appeals of differing quality. Finally, the report analyzes contrasting procedural rules used by different districts to govern social security litigation. We argue that these differences are unnecessary and create needless inefficiencies. We conclude with a set of recommendations to improve social security litigation within the federal courts

A Study of Social Security Disability Litigation in the Federal Courts

A person who has sought and failed to obtain disability benefits from the Social Security Administration (“the agency”) can appeal the agency’s decision to a federal district court. In 2015, nearly 20,000 such appeals were filed, comprising a significant part of the federal courts’ civil docket. Even though claims pass through multiple layers of internal agency review, many of them return from the federal courts for even more adjudication. Also, a claimant’s experience in the federal courts differs considerably from district to district around the country. District judges in Brooklyn decide these cases pursuant to one set of procedural rules and have in recent years remanded about seventy percent to the agency. Magistrate judges in Little Rock handle this docket with a different set of rules and have in recent years remanded only twenty percent. The adjudication of disability claims within the agency has received relentless attention from Congress, government inspectors general, academic commentators, and others. Social security litigation in the federal courts has not weathered the same scrutiny. This report, prepared for the Administrative Conference of the United States, fills this gap. It provides a comprehensive qualitative and quantitative empirical study of social security disability benefits litigation. Our report makes four contributions. The first is a thorough introduction to the process by which a disability benefits claim proceeds from initial filing to a federal judge’s chambers. This description is intended to deepen understandings of where many of federal civil cases come from, and why they raise the same sorts of concerns repeatedly. Second, the report provides some context for understanding why the federal courts remand claims to the agency at the rate that they do. We argue that the federal courts and the agency have different institutional goals, commitments, and resources. These differences would cause a sizable number of remands even if the agency adjudicated claims successfully and the federal courts applied the appropriate standard of review. Third, we undertake extensive statistical analysis to try to understand what factors explain the sharp variation in district-level remand rates. Circuit boundaries account for some, but not all, of this disparity. After excluding a number of other potential causes, we hypothesize that district courts remand claims to the agency at different rates in part because uneven adjudication within the agency produces pools of appeals of differing quality. Finally, the report analyzes contrasting procedural rules used by different districts to govern social security litigation. We argue that these differences are unnecessary and create needless inefficiencies. We conclude with a set of recommendations to improve social security litigation within the federal courts

Generating Information-Diverse Microwave Speckle Patterns Inside a Room at a Single Frequency With a Dynamic Metasurface Aperture

We demonstrate that dynamic metasurface apertures (DMAs) are capable of generating a multitude of highly uncorrelated speckle patterns in a typical residential environment at a single frequency. We use a DMA implemented as an electrically-large cavity excited by a single port and loaded with many individually-addressable tunable metamaterial radiators. We placed such a DMA in one corner of a plywood-walled L-shape room transmitting microwave signals at 19 GHz as we changed the tuning states of the metamaterial radiators. In another corner, in the non-line-of-sight of the DMA, we conducted a scan of the field generated by the DMA. For comparison, we also performed a similar test where the DMA was replaced by a simple dipole antenna with fixed pattern but generating a signal that spanned 19-24 GHz. Using singular value decomposition of the scanned data, we demonstrate that the DMA can generate a multitude of highly uncorrelated speckle patterns at a single frequency. In contrast, a dipole antenna with a fixed pattern can only generate such a highly uncorrelated set of patterns when operating over a large bandwidth. The experimental results of this paper suggest that DMAs can be used to capture a diversity of information at a single frequency which can be used for single frequency computational imaging systems, NLOS motion detection, gesture recognition systems, and more

Computational polarimetric microwave imaging

We propose a polarimetric microwave imaging technique that exploits recent advances in computational imaging. We utilize a frequency-diverse cavity-backed metasurface, allowing us to demonstrate high-resolution polarimetric imaging using a single transceiver and frequency sweep over the operational microwave bandwidth. The frequency-diverse metasurface imager greatly simplifies the system architecture compared with active arrays and other conventional microwave imaging approaches. We further develop the theoretical framework for computational polarimetric imaging and validate the approach experimentally using a multi-modal leaky cavity. The scalar approximation for the interaction between the radiated waves and the target---often applied in microwave computational imaging schemes---is thus extended to retrieve the susceptibility tensors, and hence providing additional information about the targets. Computational polarimetry has relevance for existing systems in the field that extract polarimetric imagery, and particular for ground observation. A growing number of short-range microwave imaging applications can also notably benefit from computational polarimetry, particularly for imaging objects that are difficult to reconstruct when assuming scalar estimations.Comment: 17 pages, 15 figure