Development of in situ, at-wavelength metrology for soft x-ray nano-focusing (open access)

Development of in situ, at-wavelength metrology for soft x-ray nano-focusing

At the Advanced Light Source (ALS), we are developing broadly applicable, high-accuracy, in situ, at-wavelength wavefront slope measurement techniques for Kirkpatrick-Baez (KB) mirror nano-focusing. We describe here details of the metrology beamline endstation, the at-wavelength tests, and an original alignment method that have already allowed us to precisely set a bendable KB mirror to achieve a FWHM focused spot size of ~;;120 nm, at 1-nm soft x-ray wavelength.
Date: September 19, 2010
Creator: Yuan, Sheng Sam; Yashchuk, Valeriy V.; Goldberg, Kenneth A.; Celestre, Richard; McKinney, Wayne R.; Morrison, Gregory Y. et al.
Object Type: Article
System: The UNT Digital Library
A Dual Channel X-ray Spectrometer for Fast Ignition Research (open access)

A Dual Channel X-ray Spectrometer for Fast Ignition Research

A new Dual Channel Highly Ordered Pyrolytic Graphite (DC-HOPG) x-ray spectrometer was developed to study laser-generated electron beam transport. The instrument uses a pair of graphite crystals and has the advantage of simultaneously detecting self emission from low-Z materials in first diffraction order and high-Z materials in second order. The emissions from the target are detected using a pair of parallel imaging plates positioned in a such way that the noise from background is minimized and the mosaic focusing is achieved. Initial tests of the diagnostic on Titan laser (I {approx} 10{sup 20} W/cm{sup 2}, {tau} = 0.7 ps) show excellent signal-to-noise ratio (SNR) > 1000 for the low energy channel and SNR > 400 for the high energy channel.
Date: April 19, 2010
Creator: Akli, K. U.; Patel, P. K.; Van Maren, R.; Stephens, R. B.; Key, M. H.; Higginson, D. P. et al.
Object Type: Article
System: The UNT Digital Library
Dynamics of Arctic and Sub-Arctic Climate and Atmospheric Circulation: Diagnosis of Mechanisms and Biases Using Data Assimilation (open access)

Dynamics of Arctic and Sub-Arctic Climate and Atmospheric Circulation: Diagnosis of Mechanisms and Biases Using Data Assimilation

This is the final report for DOE grant DE-FG02-07ER64434 to Eric DeWeaver at the University of Wisconsin-Madison. The overall goal of work performed under this grant is to enhance understanding of simulations of present-day climate and greenhouse gas-induced climate change. Enhanced understanding is desirable 1) as a prerequisite for improving simulations; 2) for assessing the credibility of model simulations and their usefulness as tools for decision support; and 3) as a means to identify robust behaviors which commonly occur over a wide range of models, and may yield insights regarding the dominant physical mechanisms which determine mean climate and produce climate change. A furthe objective is to investigate the use of data assimilation as a means for examining and correcting model biases. Our primary focus is on the Arctic, but the scope of the work was expanded to include the global climate system to the extent that research targets of opportunity present themselves. Research performed under the grant falls into five main research areas: 1) a study of data assimilation using an ensemble filter with the atmospheric circulation model of the National Center for Atmospheric Research, in which both conventional observations and observations of the refraction of radio waves from …
Date: January 19, 2010
Creator: DeWeaver, Eric T.
Object Type: Report
System: The UNT Digital Library
EFFECT OF PRETREATMENT ON PT-CO/C CATHODE CATALYSTS FOR THE OXYGEN-REDUCTION REACTION (open access)

EFFECT OF PRETREATMENT ON PT-CO/C CATHODE CATALYSTS FOR THE OXYGEN-REDUCTION REACTION

Carbon supported Pt and Pt-Co electrocatalysts for the oxygen reduction reaction in low temperature fuel cells were prepared by the reduction of the metal salts with sodium borohydride and sodium formate. The effect of surface treatment with nitric acid on the carbon surface and Co on the surface of carbon prior to the deposition of Pt was studied. The catalysts where Pt was deposited on treated carbon the ORR reaction preceded more through the two electron pathway and favored peroxide production, while the fresh carbon catalysts proceeded more through the four electron pathway to complete the oxygen reduction reaction. NaCOOH reduced Pt/C catalysts showed higher activity that NaBH{sub 4} reduced Pt/C catalysts. It was determined that the Co addition has a higher impact on catalyst activity and active surface area when used with NaBH{sub 4} as reducing agent as compared to NaCOOH.
Date: January 19, 2010
Creator: Fox, E. & Colon-Mercado, H.
Object Type: Article
System: The UNT Digital Library
Effects of Toroidal Rotation Sshear on Toroidicity-induced Alfven Eigenmodes in the National Spherical Torus Experiment (open access)

Effects of Toroidal Rotation Sshear on Toroidicity-induced Alfven Eigenmodes in the National Spherical Torus Experiment

The effects of a sheared toroidal rotation on the dynamics of bursting Toroidicity-induced Alfven eigenmodes are investigated in neutral beam heated plasmas on the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40 557 (2000)]. The modes have a global character, extending over most of the minor radius. A toroidal rotation shear layer is measured at the location of maximum drive for the modes. Contrary to results from other devices, no clear evidence of increased damping is found. Instead, experiments with simultaneous neutral beam and radio-frequency auxiliary heating show a strong correlation between the dynamics of the modes and the instability drive. It is argued that kinetic effects involving changes in the mode drive and damping mechanisms other than rotation shear, such as continuum damping, are mostly responsible for the bursting dynamics of the modes.
Date: August 19, 2010
Creator: Podesta, M.; Fredrickson, E. D.; Gorelenkov, N. N.; LeBlanc, B. P.; Heidbrink, W. W.; Crocker, N. A. et al.
Object Type: Report
System: The UNT Digital Library
Electrodeposition of U and Pu on Thin C and Ti Substrates (open access)

Electrodeposition of U and Pu on Thin C and Ti Substrates

Physics experiments aimed at deducing key parameters for use in a variety of programs critical to the mission of the National Laboratories require actinide targets placed onto various substrates. The target material quantity and the substrate desired depend upon the type of experiment being designed. The physicist(s) responsible for the experimental campaign will consult with the radiochemistry staff as to the feasibility of producing a desired target/substrate combination. In this report they discuss the production of U and Pu targets on very thin C and Ti substrates. The techniques used, plating cells designed for, tips, and limits is discussed.
Date: May 19, 2010
Creator: Henderson, R. A. & Gostic, J. M.
Object Type: Article
System: The UNT Digital Library
Energy Efficiency Services Sector: Workforce Education and Training Needs (open access)

Energy Efficiency Services Sector: Workforce Education and Training Needs

This report provides a baseline assessment of the current state of energy efficiency-related education and training programs and analyzes training and education needs to support expected growth in the energy efficiency services workforce. In the last year, there has been a significant increase in funding for 'green job' training and workforce development (including energy efficiency), through the American Recovery and Reinvestment Act (ARRA). Key segments of the energy efficiency services sector (EESS) have experienced significant growth during the past several years, and this growth is projected to continue and accelerate over the next decade. In a companion study (Goldman et al. 2009), our research team estimated that the EESS will increase two- to four-fold by 2020, to 220,000 person-years of employment (PYE) (low-growth scenario) or up to 380,000 PYE (high-growth scenario), which may represent as many as 1.3 million individuals. In assessing energy efficiency workforce education and training needs, we focus on energy-efficiency services-related jobs that are required to improve the efficiency of residential and nonresidential buildings. Figure ES-1 shows the market value chain for the EESS, sub-sectors included in this study, as well as the types of market players and specific occupations. Our assessment does not include the manufacturing, …
Date: March 19, 2010
Creator: Goldman, Charles A.; Peters, Jane S.; Albers, Nathaniel; Stuart, Elizabeth & Fuller, Merrian C.
Object Type: Report
System: The UNT Digital Library
Essential Boundary Conditions with Straight C1 Finite Elements in Curved Domains (open access)

Essential Boundary Conditions with Straight C1 Finite Elements in Curved Domains

The implementation of essential boundary conditions in C1 finite element analysis requires proper treatment of both the boundary conditions on second-order differentials of the solution and the curvature of the domain boundary. A method for the imposition of essential boundary conditions using straight elements (where the elements are not deformed to approximate a curved domain) is described. It is shown that pre-multiplication of the matrix equation by the local rotation matrix at each boundary node is not the optimal transformation. The uniquely optimal transformation is found, which does not take the form of a similarity transformation due to the non-orthogonality of the transformation to curved coordinates.
Date: February 19, 2010
Creator: N.M. Ferraro, S.C. Jardin, X. Luo
Object Type: Report
System: The UNT Digital Library
An Extension of Implicit Monte Carlo Diffusion: Multigroup and The Difference Formulation (open access)

An Extension of Implicit Monte Carlo Diffusion: Multigroup and The Difference Formulation

Implicit Monte Carlo (IMC) and Implicit Monte Carlo Diffusion (IMD) are approaches to the numerical solution of the equations of radiative transfer. IMD was previously derived and numerically tested on grey, or frequency-integrated problems. In this research, we extend Implicit Monte Carlo Diffusion (IMD) to account for frequency dependence, and we implement the difference formulation as a source manipulation variance reduction technique. We derive the relevant probability distributions and present the frequency dependent IMD algorithm, with and without the difference formulation. The IMD code with and without the difference formulation was tested using both grey and frequency dependent benchmark problems. The Su and Olson semi-analytic Marshak wave benchmark was used to demonstrate the validity of the code for grey problems. The Su and Olson semi-analytic picket fence benchmark was used for the frequency dependent problems. The frequency dependent IMD algorithm reproduces the results of both Su and Olson benchmark problems. Frequency group refinement studies indicate that the computational cost of refining the group structure is likely less than that of group refinement in deterministic solutions of the radiation diffusion methods. Our results show that applying the difference formulation to the IMD algorithm can result in an overall increase in the …
Date: April 19, 2010
Creator: Cleveland, M A; Gentile, N & Palmer, T S
Object Type: Article
System: The UNT Digital Library
Feasibility Studies of Alpha-Channeling in Mirror Machines (open access)

Feasibility Studies of Alpha-Channeling in Mirror Machines

The linear magnetic trap is an attractive concept both for fusion reactors and for other plasma applications due to its relative engineering simplicity and high-beta operation. Applying the α- channeling technique to linear traps, such as mirror machines, can benefit this concept by efficiently redirecting α particle energy to fuel ion heating or by otherwise sustaining plasma confinement, thus increasing the effective fusion reactivity. To identify waves suitable for α-channeling a rough optimization of the energy extraction rate with respect to the wave parameters is performed. After the optimal regime is identified, a systematic search for modes with similar parameters in mirror plasmas is performed, assuming quasi-longitudinal or quasi-transverse wave propagation. Several modes suitable for α particle energy extraction are identified for both reactor designs and for proof- of-principle experiments.
Date: March 19, 2010
Creator: Zhmoginov, A. I. & Fisch, N. J.
Object Type: Report
System: The UNT Digital Library
Final Report LDRD 04-ERD-019 Development of absolute spectroscopic diagnostics for non-LTE plasmas (open access)

Final Report LDRD 04-ERD-019 Development of absolute spectroscopic diagnostics for non-LTE plasmas

This project sought to further our understanding of non-Local Thermodynamic Equilibrium (NLTE) processes by providing benchmark data to validate computational models. This has been a difficult regime to study in the laboratory, where experimental scales produce strong gradients while interpretation requires well-characterized uniform plasmas. It has also been a difficult regime to simulate, as evidenced by the large discrepancies in predictions of NLTE spectra for fixed plasma properties. Not surprisingly, discrepancies between data and calculations of recombining laser-produced plasmas have been in evidence since the 1980's. The goal here was to obtain data of sufficient accuracy to help resolve these discrepancies and enable better modeling of the NLTE processes that are integral to high-energy density experiments. Advances in target fabrication, diagnostic development and simulation capabilities provided the foundations for this project. Uniform plasmas were to be achieved by using aerogel foams of low enough density ({approx}mg/cm{sup 3}) and thickness ({approx}mm) to be volumetrically heated by a laser. The foams were doped with Ti to provide K- and L-shell emission and recombination spectra during the experiments. A new absolutely calibrated transmission grating spectrometer provided absolute temporal measurements at 18 frequencies, in addition to a CCD image of the time-integrated spectrum. Finally, …
Date: April 19, 2010
Creator: Scott, H. A.
Object Type: Report
System: The UNT Digital Library
Fission-Fusion Neutron Source Progress Report July 31, 2009 (open access)

Fission-Fusion Neutron Source Progress Report July 31, 2009

In this report the authors describe progress in evaluating the feasibility of a novel concept for producing intense pulses of 14 MeV neutrons using the DT fusion reaction. In this new scheme the heating of the DT is accomplished using fission fragments rather than ion beams as in conventional magnet fusion schemes or lasers in ICF schemes. This has the great advantage that there is no need for any large auxiliary power source. The scheme does require large magnetic fields, but generating these fields, e.g. with superconducting magnets, requires only a modest power source. As a source of fission fragments they propose using a dusty reactor concept introduced some time ago by one of us (RC). The version of the dusty reactor that they propose using for our neutron source would operate as a thermal neutron reactor and use highly enriched uranium in the form of micron sized pellets of UC. Our scheme for using the fission fragments to produce intense pulses of 14 MeV neutrons is based on the fission fragment rocket idea. In the fission fragment rocket scheme it was contemplated that the fission fragments produced in a low density reactor core would then be guided out of …
Date: February 19, 2010
Creator: Chapline, G; Daffin, F & Clarke, R
Object Type: Report
System: The UNT Digital Library
Fission-Fusion Neutron Source Progress Report Sept 30, 2009 (open access)

Fission-Fusion Neutron Source Progress Report Sept 30, 2009

In this report the authors describe the progress made in FY09 in evaluating the feasibility of a new concept for using the DT fusion reaction to produce intense pulses of 14 MeV neutrons. In this new scheme the heating of the DT is accomplished using fission fragments rather than ion beams as in conventional magnet confinement fusion schemes or lasers in inertial confinement schemes. As a source of fission fragments they propose using a dust reactor concept introduced some time ago by one of us (RC). An attractive feature of this approach is that there is no need for a large auxiliary power source to heat the DT plasma to the point where self-sustaining fusion become possible. Their scheme does require pulsed magnetic fields, but generating these fields requires only a modest power source. The dust reactor that they propose using for their neutron source would use micron-sized UC pellets suspended in a vacuum as the reactor fuel. Surrounding the fuel with a moderator such as heavy water (D{sub 2}O) would allow the reactor to operate as a thermal reactor and require only modest amounts of HEU. The scheme for using fission fragments to generate intense pulses of 14 MeV …
Date: February 19, 2010
Creator: Chapline, G F; Daffin, F & Clark, R
Object Type: Report
System: The UNT Digital Library
Fresh Water Generation from Aquifer-Pressured Carbon Storage (open access)

Fresh Water Generation from Aquifer-Pressured Carbon Storage

Can we use the pressure associated with sequestration to make brine into fresh water? This project is establishing the potential for using brine pressurized by Carbon Capture and Storage (CCS) operations in saline formations as the feedstock for desalination and water treatment technologies including reverse osmosis (RO) and nanofiltration (NF). Possible products are: Drinking water, Cooling water, and Extra aquifer space for CO{sub 2} storage. The conclusions are: (1) Many saline formation waters appear to be amenable to largely conventional RO treatment; (2) Thermodynamic modeling indicates that osmotic pressure is more limiting on water recovery than mineral scaling; (3) The use of thermodynamic modeling with Pitzer's equations (or Extended UNIQUAC) allows accurate estimation of osmotic pressure limits; (4) A general categorization of treatment feasibility is based on TDS has been proposed, in which brines with 10,000-85,000 mg/L are the most attractive targets; (5) Brines in this TDS range appear to be abundant (geographically and with depth) and could be targeted in planning future CCS operations (including site selection and choice of injection formation); and (6) The estimated cost of treating waters in the 10,000-85,000 mg/L TDS range is about half that for conventional seawater desalination, due to the anticipated pressure …
Date: February 19, 2010
Creator: Aines, R. D.; Wolery, T. J.; Bourcier, W. L.; Wolfe, T. & Haussmann, C.
Object Type: Article
System: The UNT Digital Library
A Geochemical and Sedimentary Record of High Southern Latitude Holocene Climate Evolution from Lago Fagnano, Tierra del Fuego (open access)

A Geochemical and Sedimentary Record of High Southern Latitude Holocene Climate Evolution from Lago Fagnano, Tierra del Fuego

Situated at the southern margin of the hemispheric westerly wind belt and immediately north of the Antarctic Polar Frontal zone, Tierra del Fuego is well-positioned to monitor coupled changes in the ocean-atmosphere system of the high southern latitudes. Here we describe a Holocene paleoclimate record from sediment cores obtained from Lago Fagnano, a large lake in southern Tierra del Fuego at 55{sup o}S, to investigate past changes in climate related to these two important features of the global climate system. We use an AMS radiocarbon chronology for the last 8,000 years based on pollen concentrates, thereby avoiding contamination from bedrock-derived lignite. Our chronology is consistent with a tephrochronologic age date for deposits from the middle Holocene Volcan Hudson eruption. Combining bulk organic isotopic ({delta}{sup 13}C and {delta}{sup 15}N) and elemental (C and N) parameters with physical sediment properties allow us to better understand sediment provenance and transport mechanisms and to interpret Holocene climate and tectonic change during the last 8,000 years. Co-variability and long-term trends in C/N ratio, carbon accumulation rate, and magnetic susceptibility reflect an overall Holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin. We attribute this variability to westerly wind-derived …
Date: November 19, 2010
Creator: Moy, C M; Dunbar, R B; Guilderson, T P; Waldmann, N; Mucciarone, D A; Recasens, C et al.
Object Type: Article
System: The UNT Digital Library
HCDF: A Hybrid Community Discovery Framework (open access)

HCDF: A Hybrid Community Discovery Framework

None
Date: January 19, 2010
Creator: Henderson, Keith; Eliassi-Rad, Tina; Papadimitriou, Spiros & Faloutsos, Christos
Object Type: Article
System: The UNT Digital Library
High-efficiency 5000 lines/mm multilayer-coated blazed grating for EUV wavelengths (open access)

High-efficiency 5000 lines/mm multilayer-coated blazed grating for EUV wavelengths

Volume x-ray gratings consisting of a multilayer coating deposited on a blazed substrate can diffract with very high efficiency even in high orders if diffraction conditions in-plane (grating) and out-of-plane (Bragg multilayer) are met simultaneously. This remarkable property however depends critically on the ability to create a structure with near atomic perfection. In this work we report on a method to produce these structures. We report measurements that show, for a 5000 l/mm grating diffracting in the 3rd order, a diffraction efficiency of 37.6percent at a wavelength of 13.6 nm, close to the theoretical maximum. This work now shows a direct route to achieving high diffraction efficiency in high order at wavelengths throughout the soft x-ray energy range.
Date: April 19, 2010
Creator: Voronov, Dmitriy; Ahn, Minseung; Anderson, Erik; Cambie, Rossana; Chang, Chih-Hao; Gullikson, Eric et al.
Object Type: Article
System: The UNT Digital Library
High statistics analysis using anisotropic clover lattices: (III) Baryon-baryon interactions (open access)

High statistics analysis using anisotropic clover lattices: (III) Baryon-baryon interactions

Low-energy baryon-baryon interactions are calculated in a high-statistics lattice QCD study on a single ensemble of anisotropic clover gauge-field configurations at a pion mass of m{sub {pi}} {approx} 390 MeV, a spatial volume of L{sup 3} {approx} (2.5 fm){sup 3}, and a spatial lattice spacing of b {approx} 0.123 fm. Luescher's method is used to extract nucleon-nucleon, hyperon-nucleon and hyperon-hyperon scattering phase shifts at one momentum from the one- and two-baryon ground-state energies in the lattice volume. The isospin-3/2 N{Sigma} interactions are found to be highly spin-dependent, and the interaction in the {sup 3}S{sub 1} channel is found to be strong. In contrast, the N{Lambda} interactions are found to be spin-independent, within the uncertainties of the calculation, consistent with the absence of one-pion-exchange. The only channel for which a negative energy-shift is found is {Lambda}{Lambda}, indicating that the {Lambda}{Lambda} interaction is attractive, as anticipated from model-dependent discussions regarding the H-dibaryon. The NN scattering lengths are found to be small, clearly indicating the absence of any fine-tuning in the NN-sector at this pion mass. This is consistent with our previous Lattice QCD calculation of NN interactions. The behavior of the signal-to-noise ratio in the baryon-baryon correlation functions, and in the ratio …
Date: January 19, 2010
Creator: Beane, S; Detmold, W; Lin, H; Luu, T; Orginos, K; Savage, M et al.
Object Type: Article
System: The UNT Digital Library
Hybrid Orbital and Numerical Grid Representationfor Electronic Continuum Processes: Double Photoionization of Atomic Beryllium (open access)

Hybrid Orbital and Numerical Grid Representationfor Electronic Continuum Processes: Double Photoionization of Atomic Beryllium

A general approach for ab initio calculations of electronic continuum processes is described in which the many-electron wave function is expanded using a combination of orbitals at short range and the finite-element discrete variable representation(FEM-DVR) at larger distances. The orbital portion of the basis allows the efficient construction of many-electron configurations in which some of the electrons are bound, but because the orbitals are constructed from an underlying FEM-DVR grid, the calculation of two-electron integrals retains the efficiency of the primitive FEM-DVR approach. As an example, double photoionization of beryllium is treated in a calculation in which the 1s{sup 2} core is frozen. This approach extends the use of exterior complex scaling (ECS) successfully applied to helium and H{sub 2} to calculations with two active electrons on more complicated targets. Integrated, energy-differential and triply-differential cross sections are exhibited, and the results agree well with other theoretical investigations.
Date: April 19, 2010
Creator: Yip, Frank L; McCurdy, C. William & Rescigno, Thomas N
Object Type: Article
System: The UNT Digital Library

Hydrogen Production: Fundamentals and Case Study Summaries

This presentation summarizes hydrogen production fundamentals and case studies, including hydrogen to wind case studies.
Date: May 19, 2010
Creator: Harrison, K.; Remick, R.; Hoskin, A. & Martin, G.
Object Type: Presentation
System: The UNT Digital Library
Improved Space Charge Modeling for Simulation and Design of Photoinjectors (open access)

Improved Space Charge Modeling for Simulation and Design of Photoinjectors

Photoinjectors in advanced high-energy accelerators reduce beam energy spreads and enhance undulator photon fluxes. Photoinjector design is difficult because of the substantial differences in time and spatial scales. This Phase I program explored an innovative technique, the local Taylor polynomial (LTP) formulation, for improving finite difference analysis of photoinjectors. This included improved weighting techniques, systematic formula for high order interpolation and electric field computation, and improved handling of space charge. The Phase I program demonstrated that the approach was powerful, accurate, and efficient. It handles space charge gradients better than currently available technology.
Date: April 19, 2010
Creator: Robert H. Jackson, Thuc Bui, John Verboncoeur
Object Type: Report
System: The UNT Digital Library
The influence of displacement damage on deuterium retentionin tungsten exposed to divertor plasma in DIII-D (open access)

The influence of displacement damage on deuterium retentionin tungsten exposed to divertor plasma in DIII-D

None
Date: May 19, 2010
Creator: Wampler, W R; Rudakov, D L & Lasnier, C J
Object Type: Article
System: The UNT Digital Library
Innovative Coal Solids-Flow Monitoring and Measurement Using Phase-Doppler and Mie Scattering Techniques (open access)

Innovative Coal Solids-Flow Monitoring and Measurement Using Phase-Doppler and Mie Scattering Techniques

Fuel flow to individual burners is complicated and difficult to determine on coal fired boilers, since coal solids were transported in a gas suspension that is governed by the complex physics of two-phase flow. The objectives of the project were the measurements of suspended coal solids-flows in the simulated test conditions. Various extractive methods were performed manually and can give only a snapshot result of fuel distribution. In order to measure particle diameter & velocity, laser based phase-Doppler particle analyzer (PDPA) and particle image velocimetry (PIV) were carefully applied. Statistical methods were used to analyze particle characteristics to see which factors have significant effect. The transparent duct model was carefully designed and fabricated for the laser-based-instrumentation of solids-flow monitoring (LISM). The experiments were conducted with two different kinds of particles with four different particle diameters. The particle types were organic particles and saw dust particles with the diameter range of 75-150 micron, 150-250 micron, 250-355 micron and 355-425 micron. The densities of the particles were measured to see how the densities affected the test results. Also the experiment was conducted with humid particles and fog particles. To generate humid particles, the humidifier was used. A pipe was connected to the …
Date: January 19, 2010
Creator: Lee, Stephen Seong
Object Type: Report
System: The UNT Digital Library
Intermittent Divertor Filaments in the National Spherical Torus Experiment and Their Relation to Midplane Blobs (open access)

Intermittent Divertor Filaments in the National Spherical Torus Experiment and Their Relation to Midplane Blobs

While intermittent filamentary structures, also known as blobs, are routinely seen in the low-field-side scrape-off layer of the National Spherical Torus Experiment (NSTX) (Ono et al 2000 Nucl. Fusion 40 557), fine structured filaments are also seen on the lower divertor target plates of NSTX. These filaments, not associated with edge localized modes, correspond to the interaction of the turbulent blobs seen near the midplane with the divertor plasma facing components. The fluctuation level of the neutral lithium light observed at the divertor, and the skewness and kurtosis of its probability distribution function, is similar to that of midplane blobs seen in Dα; e.g. increasing with increasing radii outside the outer strike point (OSP) (separatrix). In addition, their toroidal and radial movement agrees with the typical movement of midplane blobs. Furthermore, with the appropriate magnetic topology, i.e. mapping between the portion of the target plates being observed into the field of view of the midplane gas puff imaging diagnostic, very good correlation is observed between the blobs and the divertor filaments. The correlation between divertor plate filaments and midplane blobs is lost close to the OSP. This latter observation is consistent with the existence of ‘magnetic shear disconnection’ due to …
Date: May 19, 2010
Creator: Maqueda, R. J. & Stotler, D. P.
Object Type: Report
System: The UNT Digital Library