Naval Research Laboratory Research Articles

Evaluation of CO2 Hydrogenation in a Modular Fixed-Bed Reactor Prototype

Low-cost iron-based CO2 hydrogenation catalysts have shown promise as a viable route to the production of value-added hydrocarbon building blocks. It is envisioned that these hydrocarbons will be used to augment industrial chemical processes and produce drop-in replacement operational fuel. To this end, the U.S. Naval Research Laboratory (NRL) has been designing, testing, modeling, and evaluating CO2 hydrogenation catalysts in a laboratory-scale fixed-bed environment. To transition from the laboratory to a commercial process, the catalyst viability and performance must be evaluated at scale. The performance of a Macrolite®-supported iron-based catalyst in a commercial-scale fixed-bed modular reactor prototype was evaluated under different reactor feed rates and product recycling conditions. CO2 conversion increased from 26% to as high as 69% by recycling a portion of the product stream and CO selectivity was greatly reduced from 45% to 9% in favor of hydrocarbon production. In addition, the catalyst was successfully regenerated for optimum performance. Catalyst characterization by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), along with modeling and kinetic analysis, highlighted the potential challenges and benefits associated with scaling-up catalyst materials and processes for industrial implementation.

High-Performance Structural Batteries

Download : Download high-res image (193KB) Download : Download full-size image Brandon J. Hopkins is a National Research Council postdoctoral fellow at the U.S. Naval Research Laboratory (NRL) focused on advancing next-generation electrochemical energy systems. Hopkins received his PhD at the Massachusetts Institute of Technology (MIT) where he worked on aqueous metal–air batteries. As a master’s candidate at MIT, he was part of the Joint Center for Energy Storage Research (JCESR) where he created gravity-driven flow batteries using semi-solid suspensions. He received his bachelor’s degree from Harvard University and interned at Akamai Technologies, Inc. and Lawrence Livermore National Laboratory. Download : Download high-res image (181KB) Download : Download full-size image Debra Rolison (left) heads and Jeffrey Long (center) and Joseph Parker (right) are members of the Advanced Electrochemical Materials Section at NRL. They design, synthesize, characterize, and prototype 3D-structured, ultraporous, multifunctional, hold-in-your-hand nanoarchitectures for such rate-critical applications as catalysis, energy storage and conversion, ultrafiltration, and sensors. They recently demonstrated that reformulating zinc into a monolithic sponge form-factor allows Zn-based batteries to be cycled at high rate to high specific energy without forming cell-shorting dendrites. They received their PhDs in Chemistry from the University of North Carolina at Chapel Hill in 1980, 1997, and 2010, respectively.

Compositing Eclipse Images from the Ground and from Space

Abstract We present composite white-light images of the 2019 July 2, total solar eclipse, from the minimum of the solar-activity cycle. We exhibit high-resolution high dynamic range composites from three observation sites in Chile, including one made of 646 individual ground-based images and with such a wide field it exceeds the field of view of the Naval Research Laboratory’s C2 and C3 coronagraphs aboard ESA’s Solar and Heliospheric Observatory. We compare the resolution of the coronal streamers and other magnetic phenomena of the corona. We also show continuity of features on the solar surface as observed from NOAA’s GOES-16 and GOES-17 Solar Ultraviolet Imager.

The Network Coordination Office of NHERI (Natural Hazards Engineering Research Infrastructure)

NHERI, or the Natural Hazards Engineering Research Infrastructure, is supported by the United States National Science Foundation (NSF) as a distributed, multi-user national facility that provides the natural hazards research community with access to a powerful research infrastructure. NHERI is comprised of separate research infrastructure awards for a Network Coordination Office (NCO), Cyberinfrastructure, a Computational Modeling and Simulation Center, eight Experimental Facilities, and CONVERGE (an initiative to advance social sciences and interdisciplinary research). Awards made for NHERI contribute to NSF's role in the National Earthquake Hazards Reduction Program and the National Windstorm Impact Reduction Program of the United States. The mission of NHERI is to provide the earthquake, wind, coastal engineering, and social sciences communities with access to research infrastructure, education, and community outreach activities focused on improving the resilience and sustainability of the civil infrastructure against earthquakes, windstorms, and associated natural events such as tsunami and coastal storm surge. In this paper, the role and key NHERI activities are described for the NCO, which is led by Purdue University, along with partner institutions—the University of Texas at San Antonio, North Carolina State University, Texas Tech University, the U.S. Naval Research Laboratory, and the University of Hawaii at Manoa. The NHERI NCO serves as a focal point and leader of a multi-hazards research community, and maintains a community-based NHERI science plan. It manages scheduling of our partner NHERI Experimental Facilities and coordinates all components to ensure effective and fair governance, efficient testing and user support within a safe environment. Another important role of the NCO is to lead NHERI-wide educational and outreach activities. The NCO works to develop strategic national and international partnerships and to coordinate NHERI activities with other awardee components to form a cohesive and fully-integrated global natural hazards engineering research infrastructure that fosters collaboration in new ways.

Does Ring Current Heating Generate the Observed O+ Shell?

AbstractThe Naval Research Laboratory (NRL) Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/plasmasphere code is used to examine the effect of ring current heating during a storm. With a ring current heating function added to SAMI3, a cold thermal (<1 eV) oxygen ion outflow is produced, with O+ density and location similar to observations of the so‐called “oxygen torus.” The ring current heating function is based on a Comprehensive Inner Magnetosphere‐Ionosphere (CIMI) model simulation of the 7 October 2015 storm. We find that the ring current can heat plasmasphere electrons, subsequently heating plasmasphere H+, and ionosphere O+. The resulting O+ outflows resemble observed O+ enhancements in the inner magnetosphere.

Analysis of UHF-band sea clutter reflectivity at low grazing angles in offshore waters of the Yellow Sea

ABSTRACT Reflectivity is an important characteristic of sea clutter that depends on the parameters of the radar and the environment. This paper presents reflectivity measurements of UHF-band horizontal polarized sea clutter based upon data collected in the offshore waters of the Yellow Sea of China at low grazing angles. During the experiment, the oceanic and meteorological conditions were recorded by the Datawell Waverider 4 and Lufft WS700-UMB on the sea surface. The factors that affect the reflectivity acquisition are analysed and the selective median filtering method in average Doppler power spectrum is presented to remove the effect of ground clutter from the sidelobes of the antenna beam pattern and the normalized reflectivity of the sea surface is computed. The applicability of the four classical reflectivity empirical models to the datasets is analysed. The results show that the Hybrid (HYB) and Technology Service Corporation (TSC) models are suitable while the Georgia Institute of Technology (GIT) and Naval Research Laboratory (NRL) models are unsuitable for the UHF-band horizontal polarized sea clutter in the offshore waters of the Yellow Sea of China.

Properties of a double-layer EMW-absorbing structure containing a graded nano-sized absorbent combing extruded and sprayed 3D printing

The ever-increasing electromagnetic wave (EMW) energy and its reflections may impair human health and information security. An ordinary EMW-absorbing structure usually exhibits limited EMW-reflecting capacity given its ungraded structure in both the micro and macro scales. In this study, four nano-sized graded absorbents are explored by wrapping carbonyl-iron powder with nano-sized silicon dioxide. The micro-scale wrapping effects are assessed via a scanning electron microscopy experiment to identify the best sample, including a 5 wt% coupling agent and a 10 wt% dispersant in CIP ethanol. The 10 mm thick concrete matching layer containing the graded absorbent is built using spraying methodology, and the 15 mm thick absorption layer is fabricated using extruding methodology. The mercury intrusion porosimetry experiments show that the sprayed matching layer incurs maximum porosity at 19.8% while the 3D extruded layer ensures the minimum porosity at 11.13%, strengthening the laminar grading effect to improve the EMW impedance matching. The Naval Research Laboratory experiments corroborate that double-layer structures improve the EMW-reflecting capacity compared to their single-absorption-layer counterparts and that the double-layer element containing the best wrapping effect absorbent yields the best reflection loss value, with a minimum of −14.7 dB and a 9.72 GHz effective bandwidth. The EMW-reflecting mechanism for the novel graded double-layer structure containing the graded nano-sized absorbent is then summarized. Theoretical calculations using the transform line theory suggest that a 15 mm absorbing layer and a 15 mm impedance matching layer is specified as the most optimized configuration, with −10.47 dB in average reflection, −15.18 dB in maximum RL, and 9.56 GHz in effective bandwidth.

U-Pu Mixed Oxide Particle Analysis by NAUTILUS and Implications for Next-Generation Verification Challenges.

Precise and accurate measurement of U and Pu isotopes from micrometer-sized particles represents new verification challenges for the International Atomic Energy Agency. The U and Pu isotopes and U-Pu elemental ratio provide valuable information about the intended use, the production process, and the purification process of Pu and mixed oxide (MOX) fuels. We demonstrate the ability to directly measure U and Pu isotopes from MOX fuel particles using the U.S. Naval Research Laboratory's Naval Ultra-Trace Isotope Laboratory's Universal Spectrometer (NAUTILUS). Reactor-grade MOX reference materials with well-characterized U and Pu isotopic composition (e.g., UKMOX10 and UKMOX100) were prepared using standard sample preparation methods for large geometry-secondary ion mass spectrometry (LG-SIMS). The results show that the NAUTILUS can discriminate the 238U1H+ signal from 239Pu+, enabling the accurate measurement of the 240Pu/239Pu ratio for MOX particles within 2σ of the certificate value for U-Pu ratios from 3:1 to 300:1. The accuracy of previously reported LG-SIMS measurements was limited to U-Pu ratios <15:1. Using the NAUTILUS, the 234U/238U, 235U/238U, 236U/238U, 240Pu/239Pu, and 242Pu/239Pu ratios for UKMOX10 and UKMOX100 can all be measured accurately within 2σ of the reference values, directly, without correction. The application of the NAUTILUS to the accurate and precise determination of the elemental and isotopic composition of MOX particles in environmental samples may unravel some emerging verification challenges in international safeguards.

Autonomous clock ensemble algorithm for GNSS applications

The US Naval Research Laboratory (NRL) has developed clock ensembles for a number of vital GNSS projects and services throughout the US and international community. Some efforts include algorithms for local realization of Coordinated Universal Time; participation in the upgrade of the Global Positioning System (GPS) system time; the initial implementation of a coherent geophysical reference time known as IGS Time (IGST); and development of various Department of Defense (DoD) capabilities for the dissemination and transfer of precise time. This paper will cover the major algorithm components that compute and maintain a robust and stable time reference for the most stringent applications mentioned here. These components include automated alert and response to clock anomalies and reduction of measurement weight in response to large clock measurement residuals. Both real and simulated data have been used to validate the ensemble algorithm and its products for reliable and robust usage in these environments.

Development of a broad bandwidth 193 nanometer laser driver for inertial confinement fusion

The U.S. Naval Research Laboratory (NRL) has built a 137 J electron beam pumped argon fluoride (ArF) laser operating at 193 nm utilizing the Electra facility. This paper highlights initial ArF oscillator measurements in the context of significant benefits of ArF laser characterization for inertial confinement fusion target performance and development of a kinetics code with predictive capabilities. Other aspects of NRL's ArF laser development program, including large scale electron beam pumped ArF amplifier development and ArF optical transport, are discussed. Initial measurements were made utilizing a quadruple pass oscillator configuration constructed in the Electra facility with a nominal 100 cm2 aperture. Laser yields between 80 and 100 J, time-dependent laser intensity, and amplified spontaneous emission (ASE) are reported over a range of gas pressure (0.8–1.4 atmospheres). Higher laser yields, 137 J, were attained in a non-optimized dual ArF oscillator configuration wherein the optical axis was rotated to conform to the measured electron beam deposition in the laser gas mixture.

The Effects of Different Shaped Baffle Blocks on the Energy Dissipation

Stilling basins can be defined as energy dissipaters constructed of the irrigation systems. This study aims at investigating the performance of the new seven baffle blocks design in terms of reducing the dimensions of stilling basins in irrigation systems. In order to assess the hydraulic efficiency of a new model for baffle block used in stilling basins, a Naval Research Laboratory (NRL) has conducted. The results of this study demonstrate that the performance of the new baffle block, in term of hydraulic jump length reduction and hydraulic energy dissipation, it's better than standard blocks. However, the ratios of the drag resistance attributed to the new baffles block (FB / F2) have been larger than that applied on the normal block. It was found that the new block dissipates the energy by 9.31% more than the concrete block, and decreases the length of the hydraulic jump by 38.6% in comparison with the standard blocks. However, the new block maximizes the drag force ratio by 98.6% in comparison with the standard baffle blocks. The findings indicated that in terms of energy reduction and dissipation in the length of the hydraulic jump, the new block is superior to the other kinds.

Fluorinated Bisphenol Sorbent Materials for Spectroscopic Chemical Threat Sensing and Photonics Applications

Alcoholic and phenolic hydrogen-bond (HB) acidic absorbents activated by fluorine chemistries have been previously developed at the U.S. Naval Research Laboratory and elsewhere to augment sorbent HB acidity, reduce sorbent HB basicity and target complementary HB basicity of a wide range of hazardous target chemicals. A significant limitation of HB sorbents developed to date has been the propensity for sorbent self-association. This intermolecular bonding between sorbent molecules hinders sorbate access to active HB acid sites in the sorbent, limiting its overall efficacy. Sorbent self-association is evidenced by broadened hydroxyl peaks in the mid-infrared (MIR) region, which can obscure important absorption frequencies that appear upon absorption of an analyte into the sorbent. In this current work our aim is to develop improved HB acidic sorbent compounds which minimize undesired sorbent self-association in order to apply these sorbents to infrared- and Raman-based sensing devices for chemical threat detection.A series of new HB acidic sorbents have been synthesized and the subsequent sorbent-sorbate interactions have been characterized by a number of methods. MIR spectroscopy has been used to help elucidate sorbent-analyte vapor interactions. The newly synthesized sorbents have been challenged with various analyte vapors, including toxic industrial chemicals, chemical warfare agent simulants, and background interferents. A particular focus of these characterization efforts has been to observe the spectral changes that occur in the hydroxyl region of the MIR upon exposure of a sorbent material to an analyte vapor. Analyte binding of an HB base occurs principally at the sorbent hydroxyl site. The resulting redshift of the hydroxyl stretching frequency is characteristic of the basicity of the analyte.These sorbent materials are specifically designed to be selective toward hazardous chemicals through complementary hydrogen-bonding interactions between sorbent and analyte molecules. Generally, common interferents, such as hydrocarbons, have little or no hydrogen-bond basicity, while hazardous chemicals of interest have moderate to high basicity. More strongly HB basic analytes trigger larger redshifts of the hydroxyl absorption frequency. Benchtop FTIR characterization has confirmed that these newly designed sorbent materials are responsive to threat chemicals of interest at low concentrations and largely unresponsive to interferent chemicals, even at relatively high concentrations.Based on the strong affinity of these sorbents to threat chemicals of interest and the significant spectral changes that occur in the MIR upon formation of the hydrogen-bonded complex, these sorbent materials make useful candidates for MIR sensing applications. A frequency shift of the hydroxyl stretch indicates a sorbate has formed a HB with the sorbent. The magnitude of the frequency shift correlates with the basicity of the analyte, which is indicative of the class of compound to which the newly bound chemical belongs. In a sensing application, this feature can provide an alert that a hazardous chemical is present, even if it is an unknown threat. While the hydroxyl region allows for class specificity of unknown compounds, the fingerprint region complexity may facilitate specific analyte recognition. At present, this work has been focused on analysis of the hydroxyl region and distinction of different classes of compounds, but future efforts will turn to the fingerprint region to provide an avenue for specific chemical identification.Raman spectroscopy has also been used to characterize these sorbent materials. Specifically, a technique known as waveguide-enhanced Raman spectroscopy (WERS) has been used, which features the use of highly evanescent, low-loss waveguides with the sorbent material as a top cladding.2 WERS can be achieved using an incredibly small footprint with a sorbent-functionalized nanophotonic waveguide that is approximately a few centimeters long. Using WERS, the differential Raman spectra of the sorbent material interacting with different chemical warfare agent simulants has been measured at parts-per-billion detection levels. The spectra exhibit extrapolated three-sigma detection limits as low as 3 ppb. Continuing efforts are focused on adapting this technique to photonic integrated circuit-based fabrication and chip-scale Raman spectroscopy for trace chemical vapor detection.This presentation will highlight the design of these next-generation sorbents as a tool to facilitate MIR- and Raman-based sensing of threat chemicals. It will focus on analyzing sorbent-analyte spectral interactions and discuss how to exploit these features to develop MIR- and Raman-based sensors.

Investigation of sources of gravity waves observed in the Brazilian equatorial region on 8 April 2005

Abstract. On 8 April 2005, strong gravity wave (GW) activity (over a period of more than 3 h) was observed in São João do Cariri (7.4∘ S, 36.5∘ W). These waves propagated to the southeast and presented different spectral characteristics (wavelength, period and phase speed). Using hydroxyl (OH) airglow images, the characteristics of the observed GWs were calculated; the wavelengths ranged between 90 and 150 km, the periods ranged from ∼26 to 67 min and the phase speeds ranged from 32 to 71 m s−1. A reverse ray-tracing analysis was performed to search for the possible sources of the waves that were detected. The ray-tracing database was composed of temperature profiles from the Naval Research Laboratory Mass Spectrometer Incoherent Scatter (NRLMSISE-00) model and SABER measurements as well as wind profiles from the Horizontal Wind Model (HWM) and meteor radar data. According to the ray tracing result, the likely source of these observed gravity waves was the Intertropical Convergence Zone, which caused intense convective processes to take place in the northern part of the observatory. Also, the observed preferential propagation direction of the waves to the southeast could be explained using blocking diagrams, i.e. due to the wind filtering process.

Pulsed Power as a Science: Predictive Simulations for Beams, Z-Pinches, and Other Applications

This article is based on my plenary presentation that was associated with my Peter Haas Award, where I overview my 40 years of research and the people with whom I have had the pleasure of working, both domestically and internationally. In 1978, Sandia’s electron beam fusion program emerged from a weapons simulator community that was machine oriented and relied on design principles and J. Charlie Martin (JCM) criteria. The simulation tools were primarily used retrospectively. Fusions’ extraordinary requirements stimulated tremendous innovation in pulsed power, beams, pinches, and simulation tools. I started by developing ion beam deposition and transport models that were integrated into radiation-hydrodynamics codes; validated by experiments on Gamble II and Proto I; and helped initiate Sandia’s light-ion-beam fusion program. Strategic Defense Initiative (SDI) program research led to the development of the Integrated Tiger Series (ITS) suite of electron–photon Monte Carlo codes (1985). A research on Particle Beam Fusion Accelerator I (PBFA-I) and PBFA-II on generating, transporting, and focusing ion beams required developing transport, diagnostic simulation, and analysis tools, which were used in focusing protons to 5 TW/cm2 (1991) and lithium beams to 2 TW/cm2 and heating hohlraums to 65 eV (1996). They also helped identify anode plasma formation by electron heating as the source of diode impedance collapse leading to efforts to include electron–electrode interaction models into particle-in-cell (PIC) codes and initiating hybrid fluid-PIC development (IPROP, LSP). Electrode physics remains a power flow grand challenge for high-yield fusion. In 1999, I led rad-magnetohydrodynamic (MHD) development [arbitrary-Lagrangian–Eulerian general research applications high-energy-density physics (ALEGRA-HEDP)] and oversaw equation of state (EOS) and conductivity model development using quantum molecular dynamics/density function theory (QMD/DFT), resulting in predictive capabilities for dynamic material experiments. Improved z-pinch dynamic hohlraum modeling and experiments resulted in thermonuclear neutrons (2004). 3-D wire array dynamics were modeled and understood. We developed advanced radiographic sources and built a linear transformer driver (LTD) test bed. At the Naval Research Laboratory (NRL), I have overseen advances in modeling and experiments in beams, pinches, pulsed power, and their applications (2009-). My goal throughout has been to develop and validate predictive simulation tools, making pulsed power a Science.

A New Data Set of Thermospheric Molecular Oxygen From the Global‐scale Observations of the Limb and Disk (GOLD) Mission

AbstractThe Global‐scale Observations of the Limb and Disk (GOLD) instrument was launched on 25 January 2018 onboard the SES‐14 commercial communications satellite and began nominal science operations in October 2018. Operating from geostationary orbit at 47.5°W longitude, GOLD images the Earth's thermosphere and ionosphere in the far‐ultraviolet (132–162 nm), measuring critical geophysical parameters by continuously scanning the Earth's disk and limb 18 hours per day. GOLD also performs stellar occultation measurements using bright type O and B stars. Up to 10 occultations per day are obtained at latitudes ranging from 60°S to 45°N and two fixed longitudes, ~33°E and ~128°W. The occultation data provide a direct measurement of atmospheric absorption in the O2 Schumann Runge continuum, which is used to retrieve the O2 density profile from 130‐ to 200‐km altitude. This paper describes the GOLD occultation measurement technique and the operational retrieval algorithm used to derive the Level 2 O2DEN data product. The spatial, temporal, and local time sampling of the GOLD O2 data product is summarized, and the data quality, retrieval errors, and validation plans are discussed. Occultations are observed under both daytime and nighttime conditions, providing the O2 density over a complete range of local times. GOLD retrievals have an estimated precision of 10% and a vertical resolution of 5–10 km, depending on altitude. The data have sufficient accuracy and resolution to provide scientifically useful constraints on the O2 abundance and variability. Initial comparisons show qualitative agreement, but also notable differences, between the GOLD O2 data and the Naval Research Laboratory Mass Spectrometer Incoherent Scatter Radar (NRLMSISE‐00) empirical model predictions.

SAMI3 Simulations of Ionospheric Metallic Layers at Arecibo

AbstractThe Naval Research Laboratory Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/plasmasphere code is used to examine the physics of metallic layers at altitudes from 80 to 160 km. Results are presented near the simulated location of the Arecibo observatory (18°N, 66°W). We find that simulations, using winds from the empirical horizontal wind model, produce layers consistent with those observed at Arecibo. Specifically, we find upper semidiurnal and lower diurnal traces similar to those identified in previous observational surveys. While metallic layers are shaped by meridional winds, zonal winds, and electric fields, much of the observed structure is produced if only meridional wind forces are included in the model. Stratification below 110 km, where the ions are very weakly magnetized, is supported mainly by meridional wind shear.

Comment on “Radiation-Belt Remediation Using Space-Based Antennas and Electron Beams” by Carlsten et al.

In a recent article, Carlsten et al. state “VLF modes in the ionosphere can be driven either by an antenna or by an electron beam” and dismiss the U.S. Naval Research Laboratory (NRL) concept of producing the very low frequency (VLF) waves by high-speed neutral atom injection perpendicular to the magnetic field as “impractical.” In this comment, we highlight that the scientific basis used to make this conclusion is dubious and point to published literature that refutes this conclusion that was not cited in their article.

Response to Comment on “Radiation-Belt Remediation Using Space-Based Antennas and Electron Beams” by G. Ganguli and C. Crabtree

Ganguli and Crabtree have written a comment about a recent article by the authors listed above on radiation-belt remediation. They have objected to our evaluation of the Naval Research Laboratory's chemical release concept which states that this concept may be impractical due to an apparently low overall efficiency. In their comment, they provide a scientific argument and refer to the published literature to counter our statement. Here, we provide more details on our numerical calculations and experimental results which led to this evaluation.

A New Method for Deriving the Nightside Thermospheric Density Based on GUVI Dayside Limb Observations

AbstractWe propose a new method to derive the nightside thermospheric density by extending Global Ultraviolet Imager (GUVI) dayside limb observations using empirical orthogonal function (EOF) analysis. First, we acquire the GUVI dayside total mass density during 2002–2005 to construct a preliminary empirical model (EM). Simultaneously, we decompose the background thermospheric density from U.S. Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Extended model into different EOFs. The decomposed EOFs are then used to fit the continuous density from EM, to develop a new nightside extended model (NEM). The preliminary EM and developed NEM are further evaluated with Challenging Minisatellite Payload (CHAMP) satellite observations. Higher correlation coefficients and smaller relative standard errors between CHAMP observations and the NEM results are obtained than those between CHAMP observations and the EM results, and the NEM results are in good agreement with the CHAMP observations in time series during both daytime and nighttime, which all prove the NEM method is effective to the reproduction and extension of GUVI original dayside observations. Furthermore, the NEM reveals two typical seasonal variation features, the semiannual variation and equinoctial asymmetry of thermospheric density. The model provides an effective tool to derive the nightside thermospheric density and explore the thermospheric intrinsic structure, and needs the further development to achieve more widespread application of the thermosphere.

Spatial distribution of ion emission in gas-puff z-pinches and dense plasma foci

Mega-ampere dense plasma foci and deuterium gas-puff z-pinches can accelerate deuterons to multi-MeV energies. Diagnostic measurements of the properties of these ions provide information about ion acceleration in z-pinch plasmas. In particular, the results from ion pinhole cameras seem to be useful for the discussion of ion acceleration mechanisms. Recently, we have used various configurations of ion pinhole cameras in deuterium gas-puff experiments on the GIT-12 generator at the Institute of High Current Electronics in Tomsk and on the HAWK generator at the US Naval Research Laboratory in Washington. The stack of radiochromic films and CR-39 solid-state nuclear track detectors recorded deuterons with energies up to 30 MeV. From our ion diagnostics, we obtained the spatial distribution of the ion source and the ion-beam divergence during the ion emission. This ion-beam divergence was found to decrease with increasing deuteron energy. At 20 MeV, the divergence of each of the individual micro-beams that composed the ion source was on the order of 10 mrad. The deflection of each micro-beam due to the azimuthal magnetic and/or radial electric fields resulted in radial stripes observed by the beam-profile detectors. By analyzing the ion pinhole images, we found that the deuterons were emitted both from a central spot and from a ring-shaped region with a rather large diameter, on the order of 1 cm. The origin and particular diameter of this ring is attributed to the geometry of the electrodes and to the distribution of the current density before the disruption.