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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on KY(NbCl3)6 by Materials Project

KY(NbCl3)6 crystallizes in the trigonal R3 space group. The structure is three-dimensional. K1+ is bonded to twelve Cl1- atoms to form KCl12 cuboctahedra that share corners with three equivalent YCl6 octahedra, corners with six NbCl5 square pyramids, edges with three equivalent NbCl5 square pyramids, and faces with three equivalent NbCl5 square pyramids. The corner-sharing octahedral tilt angles are 51°. There are a spread of K–Cl bond distances ranging from 3.53–3.62 Å. Y3+ is bonded to six Cl1- atoms to form YCl6 octahedra that share corners with three equivalent KCl12 cuboctahedra and corners with six NbCl5 square pyramids. There are three shorter (2.66 Å) and three longer (2.71 Å) Y–Cl bond lengths. There are two inequivalent Nb+2.33+ sites. In the first Nb+2.33+ site, Nb+2.33+ is bonded to five Cl1- atoms to form NbCl5 square pyramids that share a cornercorner with one KCl12 cuboctahedra, a cornercorner with one YCl6 octahedra, corners with four NbCl5 square pyramids, and a faceface with one KCl12 cuboctahedra. The corner-sharing octahedral tilt angles are 46°. There are a spread of Nb–Cl bond distances ranging from 2.46–2.72 Å. In the second Nb+2.33+ site, Nb+2.33+ is bonded to five Cl1- atoms to form NbCl5 square pyramids that share a cornercorner with one KCl12 cuboctahedra, a cornercorner with one YCl6 octahedra, corners with four NbCl5 square pyramids, and an edgeedge with one KCl12 cuboctahedra. The corner-sharing octahedral tilt angles are 45°. There are a spread of Nb–Cl bond distances ranging from 2.47–2.71 Å. There are six inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a distorted bent 150 degrees geometry to one Y3+ and one Nb+2.33+ atom. In the second Cl1- site, Cl1- is bonded in a 2-coordinate geometry to one K1+ and two equivalent Nb+2.33+ atoms. In the third Cl1- site, Cl1- is bonded in a 3-coordinate geometry to one K1+ and two equivalent Nb+2.33+ atoms. In the fourth Cl1- site, Cl1- is bonded in a 2-coordinate geometry to two Nb+2.33+ atoms. In the fifth Cl1- site, Cl1- is bonded in a 3-coordinate geometry to one K1+ and two Nb+2.33+ atoms. In the sixth Cl1- site, Cl1- is bonded in a 3-coordinate geometry to one K1+, one Y3+, and one Nb+2.33+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KY(TeO3)2 by Materials Project

KY(TeO3)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.88–3.13 Å. Y3+ is bonded in an octahedral geometry to six O2- atoms. There are a spread of Y–O bond distances ranging from 2.26–2.31 Å. There are two inequivalent Te4+ sites. In the first Te4+ site, Te4+ is bonded in a 3-coordinate geometry to three O2- atoms. There is two shorter (1.89 Å) and one longer (1.90 Å) Te–O bond length. In the second Te4+ site, Te4+ is bonded in a distorted trigonal non-coplanar geometry to three O2- atoms. All Te–O bond lengths are 1.89 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Y3+ and one Te4+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one K1+, one Y3+, and one Te4+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+, one Y3+, and one Te4+ atom. In the fourth O2- site, O2- is bonded to two equivalent K1+, one Y3+, and one Te4+ atom to form a mixture of distorted edge and corner-sharing OK2YTe tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Nucleon resonance structure studies via exclusive KY electroproduction

Studying the structure of excited nucleon states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The electrocouplings of $N^*$ states in the mass range below 1.8~GeV have been determined from analyses of CLAS $\pi N$, $\eta N$, and $\pi \pi N$ data. This work has made it clear that consistent results from independent analyses of several exclusive channels with different couplings and non-resonant backgrounds but the same $N^*$ electro excitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic coupling, many high-lying $N^*$ states preferentially decay through the $\pi \pi N$ channel instead of $\pi N$. Data from the $KY$ channels will therefore be critical to provide an independent analysis to compare the extracted electrocouplings for the high-lying $N^*$ states against those determined from the $\pi N$ and $\pi \pi N$ channels. Lastly, a program to study excited $N^*$ state structure in both non-strange and strange exclusive electroproduction channels using CLAS12 will measure differential cross sections and polarization observables to be used as input to extract the $\gamma_vNN^*$ electrocoupling amplitudes for the most prominent $N^*$ states in the range of invariant energy $W$ up 3~GeV in the virtually unexplored domain of momentum transfers $Q^2$ up to 12~GeV$^2$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Near-infrared-to-near-infrared down-shifting and upconversion luminescence of KY{sub 3}F{sub 10} with single dopant of Nd{sup 3+} ion

We have studied the structural and near-infrared (NIR) luminescent properties of KY{sub 3}F{sub 10} phosphors, singly doped with Nd{sup 3+} serving as both sensitizer and activator. With a single laser diode at the wavelength of 808 nm as a pump source, simultaneous NIR-to-NIR upconversion (UC) and down-shifting (DS) emissions are effectively achieved, due to the specific energy levels of Nd{sup 3+} dopant and the low phonon energy of the host. The luminescence mechanism related to energy transfer is discussed. The luminescence can be modulated through controlling the population of Nd{sup 3+}:{sup 4}F{sub 3/2} state in our experiment. Interestingly, both UC and DS emissions of the material fall within the dual biological window, suggesting that the prepared phosphors have potential applications in the bioimaging field.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRSDate not supplied

Formational History and Geomorphic Preservation of Sea Level Highstands Over the Last 150 ky Near Cape Canaveral, Florida, USA

Cape Canaveral, Florida, is perhaps one of the most important stretches of coastline in the United States of America (USA) due to its critical strategic role in the pursuit of space exploration and as the locus of advanced technological innovation. Due to its geographical setting, the entirety of Cape Canaveral, including its infrastructure, facilities, and important natural habitats (e.g., wetlands, estuaries and dunes) is vulnerable to coastal hazards such as continued sea level rise, storm surges, erosion and flooding. As such, accurate sea level characterization and coastal resiliency predictions are essential to promoting long-term coastal planning and sustainability in the area. This study aims to better understand the temporal and spatial evolution of this area with the purpose of more accurately documenting historical sea level fluctuations and calibrating more localized projections at this site. The Cape Canaveral coastline is situated on a passive margin mostly affected by oceanic (sea level change and wave impact) and atmospheric (aeolian) alteration. This sector is part of the east Florida coast microtidal (1.2 m) setting and low wave energy (1.2-1.6 m and 6.1-8.2 sec for average significant waves) regime and is defined by a well delineated set of beach ridge or cape systems. While the name “Cape Canaveral” is often used as a generic term to describe the geographic area, it is actually an amalgamation or complex of multiple preserved capes. The preserved Cape Canaveral beach ridge plain has largely documented the paleo-sea level highstand history over the last 150 ky. High-resolution mapping of these beach ridges is completed using GPS, LiDAR, aerial, as well as satellite imagery. In order to reconstruct the formational history of the Cape Kennedy Complex and the preserved record of sea level highstands, these detailed geomorphological observations are integrated with OSL and C14 dating techniques. The chronological framework delineated by the OSL dates coupled with detailed geomorphological mapping allows for the creation of high-resolution calibrated site-specific sea level curves that reflect the local environmental and geological conditions. This refinement has the potential to improve the understanding of past sea level variability which is crucial for predicting future trends and assessing the impacts on coastal regions such as Cape Canaveral.

geomorphology↗
DOE OSTI2020

Session 077 - Panel: Wednesday US DOE Featured Site: Lexington, KY Office (Portsmouth and Paducah Sites) (R1.14)

This panel featured the DoE's Portsmouth Paducah Project Office (PPPO), which is responsible for the management and cleanup of at the Portsmouth, Ohio and Paducah, Kentucky former Gaseous Diffusion Plant sites. Portsmouth is primed for the first major skyline change at the site the upcoming demolition of the X-326 process building and initial operations of the Onsite Waste Disposal Facility. The Paducah site is working on the C-400 city block initiative allowing DOE to tackle the main source of groundwater contamination at the site, in conjunction with deactivation and demolition of the C-400 Cleaning Building. PPPO's DUF6 conversion plants have 7 lines in continuous operation at both sites providing the opportunity to ramp up cylinder processing. Panelists with presentations: DOE PPO Update (Robert Edwards, Joel Bradburne); Portsmouth/Paducah Project Office (PPPO) (Joel Bradburne, Robert Edwards); PADUCAH (Jennifer Woodard, Myrna Espinosa Redfield); Depleted Uranium Hexafluoride Conversion Project (Reinhard Knerr, Zack Smith); Paducah Deactivation and Remediation Project (Myrna Espinosa Redfield); Mid-America Conversion Services - Seven Lines One Project (Zack Smith)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2013

Mechanisms of G1 cell cycle arrest and apoptosis in myeloma cells induced by hybrid-compound histone deacetylase inhibitor

Highlights: •Novel histone deacetylase inhibitor Ky-2, remarkably inhibits myeloma cell growth. •Ky-2 demonstrates no cytotoxicity against normal lymphocytic cells. •Ky-2 induces cell cycle arrest through the cell cycle-associated proteins. •Ky-2 induces Bcl-2-inhibitable apoptosis through a caspase-dependent cascade. -- Abstract: Objectives: Histone deacetylase (HDAC) inhibitors are new therapeutic agents, used to treat various types of malignant cancers. In the present study, we investigated the effects of Ky-2, a hybrid-compound HDAC inhibitor, on the growth of mouse myeloma cells. Materials and methods: Myeloma cells, HS-72, P3U1, and mouse normal cells were used in this study. Effect of HDAC inhibitors on cell viability was determined by WST-assay and trypan blue assay. Cell cycle was analyzed using flow cytometer. The expression of cell cycle regulatory and the apoptosis associated proteins were examined by Western blot analysis. Hoechst’s staining was used to detect apoptotic cells. Results: Our findings showed that Ky-2 decreased the levels of HDACs, while it enhanced acetylation of histone H3. Myeloma cell proliferation was inhibited by Ky-2 treatment. Interestingly, Ky-2 had no cytotoxic effects on mouse normal cells. Ky-2 treatment induced G1-phase cell cycle arrest and accumulation of a sub-G1 phase population, while Western blotting analysis revealed that expressions of the cell cycle-associated proteins were up-regulated. Also, Ky-2 enhanced the cleavage of caspase-9 and -3 in myeloma cells, followed by DNA fragmentation. In addition, Ky-2 was not found to induce apoptosis in bcl-2 overexpressing myeloma cells. Conclusion: These findings suggest that Ky-2 induces apoptosis via a caspase-dependent cascade and Bcl-2-inhibitable mechanism in myeloma cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

University of Louisville Research and Energy Independence Program

The development of domestic, environmentally friendly and sustainable sources of energy and liquid fuel is a critical need for the United States (US). Kentucky (KY) is rich in natural energy and agricultural resources that could provide sustainable energy for the state and for the nation. New technology is needed to capture, store, and distribute this sustainable energy in KY. Development of KY’s sustainable energy resources will create economic benefit for the citizens of KY and can serve as a model for other states in the US. Existing technologies for solar energy collection and storage are practical for regions with high and consistent solar intensity, such as the southwest US. Solar energy is plentiful in KY, but is less intense and less regular. As such, novel innovative technology is needed to capture, store, and distribute this energy. KY also has plentiful biomass resources that can be converted to renewable fuels. In addition, the state offers low energy rates, which are conducive for any type of manufacturing industry. A manufacturing R&D center at the University of Louisville (UofL) can help attract high-tech manufacturing industries to the city of Louisville and the state of KY.

09 BIOMASS FUELS↗
DOE OSTI2020

Mercury linked to Deccan Traps volcanism, climate change and the end-Cretaceous mass extinction

Mercury (Hg) anomalies linked to Large Igneous Provinces (LIP) volcanism have been identified in sediments across all five major mass extinctions in Earth's history. This study tests whether Hg in marine sediments is a reliable proxy linking Deccan Traps volcanic eruptions to late Maastrichtian global climate warming and the mass extinction at the Cretaceous-Paleogene boundary (KPB). Our primary test site is the Elles section in Tunisia, the auxiliary Global Stratotype Section and Point (GSSP) to El Kef. Elles has the most complete marine sedimentary record and a high average sedimentation rate of ~4.7 cm/ky. Here, we chose the Hor Hahar section in Israel to corroborate the geographic distribution of Hg fallout from Deccan volcanism. Reliability of the Hg proxy over the last 550 ky of the Maastrichtian to early Danian was evaluated based on high-resolution age control (orbital cyclostratigraphy), stable isotope climate record, Hg concentrations, biotic turnover and mass extinction. These results were correlated with the pulsed Deccan eruptive history constrained previously by U-Pb zircon geochronology. Our results support Hg as robust proxy for Deccan volcanism with large Hg spikes marking “extreme event” (EE) pulsed eruptions correlative with climate warming peaks separated by steady, less intense eruptions. Long-term global climate warming began near ~350 ky pre-KPB, reached maximum warming (3–4 °C) between 285 and 200 ky pre-KPB, followed by gradual cooling and rapid temperature drop between 45 and 25 ky pre-KPB. During the last 25 ky before the KPB, multiple Hg EE eruptions correlate with hyperthermal warming that culminated in the rapid mass extinction at Elles during ≤1000 years of the Cretaceous. These latest Cretaceous Hg peaks may correlate with massive, distal, Deccan-sourced lava flows (>1000 km long) that traversed the Indian subcontinent and flowed into the Bay of Bengal, bracketing the mass extinction. These results support Deccan volcanism as a primary driver of the end-Cretaceous mass extinction.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1987

U-238-U-234-Th-230-Th-232 systematics and the precise measurement of time over the past 500,000 years

A method is presented for the high-precision measurement of the Th-230 abundance in corals by isotope-dilution mass spectrometry using techniques developed by Chen and Wasserburg (1980, 1981) and Chen et al. (1986). It is shown that 6 x 10 to the 8th atoms of Th-230 can be measured to + or - 30 percent (2 sigma) and 2 x 10 to the 10th atoms of Th-230 to + or - 2 percent. The time over which useful age data on corals can be obtained ranges from a few years to about 500 ky, with the uncertainty in age ranging from 5 y for a 180-y-old coral, to 44 y for a 8294-y-old coral, to 1.1 ky for a 123.1-ky-old coral. Ages were determined with high analytical precision for several corals that grew during high sea-level stands about 120 ky ago, supporting the view that the dominant cause of Pleistocene climate change was Milankovitch forcing.

Edwards, R. Lawrence↗
NASA NTRS1999

Cosmogenic Radionuclides in Hot Desert Chondrites with Low C-14 Activities: A Progress Report

Terrestrial ages of meteorites from hot deserts provide an important tool to estimate meteorite fluxes to the Earth. Most desert meteorites have terrestrial ages less than 40 ky, but a few achondrites from the Sahara region were recently shown to have significantly higher ages, up to approx. 100 ky. In general, C-14 (half-life = 5730 y) is the most suited radionuclide to determine terrestrial ages for desert meteorites. However for meteorites with ages greater than 35 ky, the concentration of cosmogenic C-14 has decreased to a level at which it becomes difficult to distinguish between cosmogenic C-14 and terrestrial contamination. These meteorites may therefore be much older than 35 ky. We selected chondrites with low C-14 activities (less than or equal to 2 dpm/kg) for measurements of the concentrations of cosmogenic Cl-36 (half-life= 3.01 x 10 (exp 5) y) and Ca-41 (half-life= 1.04 x 10 (exp 5) y) in the metal phase. Since the ratio of Ca-14/Cl-36 in the metal phase of chondrites is relatively constant and well known, the measured ratio is a direct measure of the terrestrial age. A major problem is that most or sometimes all of the metal in these old "hot desert" meteorites has been oxidized to hydrated Fe-Ni-oxides. Therefore, we also measured the concentrations of Be-10, Al-26 and Cl-36 in the stony phase in order to constrain the terrestrial age as much as possible.

Welten, Kees↗
NASA NTRS2000

Cosmogenic Radionuclides in Hot Desert Chondrites With Low C-14 Activities

Terrestrial ages of meteorites from hot deserts provide an important tool to estimate meteorite fluxes to the Earth. Most desert meteorites have terrestrial ages less than 40 ky, but a few achondrites from the Sahara region were recently shown to have significantly higher ages, up to approx.100 ky. In general, C-14 (half-life = 5730 y) is the most suited radionuclide to determine terrestrial ages for desert meteorites. However for meteorites with ages >35 ky, the concentration of cosmogenic C-14 has decreased to a level at which it becomes difficult to distinguish between cosmogenic C-14 and terrestrial contamination. These meteorites may therefore be much older than 35 ky. We selected chondrites with low C-14 activities (less than or equal to 2 dpm/kg) for measurements of the concentrations of cosmogenic Cl-36 (half-life= 3.01 x 10(exp 5) y) and Ca-41 (half-life= 1.04 x 10(exp 5) y) in the metal phase. Since the ratio of Ca-41/Cl-36 in the metal phase of chondrites is relatively constant and well known, the measured ratio is a direct measure of the terrestrial age]. A major problem is that most or sometimes all. of the metal in these old "hot desert" meteorites has been oxidized to hydrated Fe-Ni-oxides. Therefore, we also measured the concentrations of Be-10, Al-26 and Cl-36 in the stony phase in order to constrain the terrestrial age as much as possible.

Welten, K. C.↗
NASA NTRS1992

Modeling 100,000-year climate fluctuations in pre-Pleistocene time series

A number of pre-Pleistocene climate records exhibit significant fluctuations at the 100,000-year (100-ky) eccentricity period, before the time of such fluctuations in global ice volume. The origin of these fluctuations has been obscure. Results reported here from a modeling study suggest that such a response can occur over low-altitude land areas involved in monsoon fluctuations. The twice yearly passage of the sun across the equator and the seasonal timing of perihelion interact to increase both 100-ky and 400-ky power in the modeled temperature field. The magnitude of the temperature response is sufficiently large to leave an imprint on the geologic record, and simulated fluctuations resemble those found in records of Triassic lake levels.

Crowley, Thomas J.↗
DOE OSTI2018

CLAS N* Excitation Results from Pion and Kaon Electroproduction

The study of the structure of excited nucleon $N^*$ states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The electrocouplings of $N^*$ states in the mass range below $W$=1.8~GeV have been determined from analyses of CLAS $\pi N$, $\eta N$, and $\pi \pi N$ data at four-momentum transfers $Q^2$ up to 5~GeV$^2$. The work has made it clear that consistent results from independent analyses of several exclusive channels with different couplings and non-resonant backgrounds but the same $N^*$ electroexcitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic couplings, many high-lying $N^*$ states preferentially decay through the $\pi \pi N$ channel, while couplings to $\pi N$ final states become rather small. The resonance parameters determined from $\pi N$ and $\pi \pi N$ electroproduction can be checked in independent studies of the $KY$ ($Y = \Lambda, \Sigma^0$) channels. Therefore, data from the $KY$ channels already measured with CLAS will play an important role in $N^*$ structure studies. These comparisons await the development of suitable reaction models. Starting in 2018, a program to study the structure of $N^*$ states in various exclusive electroproduction channels using the new CLAS12 spectrometer will get underway. These studies will probe the structure of $N^*$ states in the mass range up to $W$=3~GeV and $Q^2$ up to 12~GeV$^2$, thus providing a means to access $N^*$ structure information spanning a broad regime encompassing both low- and high-energy degrees of freedom.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Morphology-controlled synthesis, growth mechanism and fluorescence of YF{sub 3}:Eu{sup 3+}, Bi{sup 3+}

Highlights: • YF3:0.125Eu3+, 0.5%Bi3+ with spherical, truncated octahedron, octahedron and pseudo-sphere particle have been controllably obtained. • The possible growth mechanism for diverse morphologies has been proposed. • Fluorescent properties are also tailored by changing the synthetic parameters of reaction temperature and dwelling time. - Abstract: In recent years, morphology-controlled synthesis and corresponding property tuning in inorganic materials have attracted considerable attention. In this work, lanthanide luminescent materials of YF{sub 3}:0.125Eu{sup 3+}, 0.5%Bi{sup 3+} with a variety of well-defined morphologies including spherical, truncated octahedron, octahedron and pseudo-sphere particle have been controllably synthesized via a facile hydrothermal method. Phase structure and morphology of the materials are tuned, and thus fluorescent properties are tailored by changing the synthetic parameters of reaction temperature and dwelling time. With increasing reaction temperature, the materials are transformed from KY{sub 3}F{sub 10} to YF{sub 3}, and the morphology varies from spherical to octahedron and finally truncated octahedra. When dwelling time increases, the samples also extend from KY{sub 3}F{sub 10} to YF{sub 3} and the morphology changes from spherical to octahedron, then truncated octahedra and finally pseudo-sphere particle. The possible growth mechanism for diverse morphologies has been proposed. The fluorescence intensity of the materials is closely related to their morphologic characteristics. The YF{sub 3}:0.125Eu{sup 3+}, 0.5%Bi{sup 3+} with truncated octahedra synthesized at 200 °C for 18 h presents the strongest emission intensity because of its less defects sites and large grain size. In addition, it has been demonstrated that the present luminescent materials can be potentially used as the luminescent ink.

36 MATERIALS SCIENCE↗
DOE OSTI2012

An Alternative View of the Dynamical Origin of the P11 Nucleon Resonances: Results from the Excited Baryon Analysis Center

We present an alternative interpretation for the dynamical origin of the P{sub 11} nucleon resonances, which results from the dynamical coupled-channels analysis at Excited Baryon Analysis Center of Jefferson Lab. The results indicate the crucial role of the multichannel reaction dynamics in determining the N* spectrum. An understanding of the spectrum and structure of the excited nucleon (N*) states is a fundamental challenge in the hadron physics. The N* states, however, couple strongly to the meson-baryon continuum states and appear only as resonance states in the {gamma}N and {pi}N reactions. One can expect from such strong couplings that the (multichannel) reaction dynamics will affect significantly the N* states and cannot be neglected in extracting the N* parameters from the data and giving physical interpretations. It is thus well recognized nowadays that a comprehensive study of all relevant meson production reactions with {pi}N,{eta}N,{pi}{pi}N,KY, {hor_ellipsis} final states is necessary for a reliable extraction of the N* parameters. To address this challenging issue, the Excited Baryon Analysis Center (EBAC) of Jefferson Lab has been conducting the comprehensive analysis of the world data of {gamma}N,{pi}N {yields} {pi}N,{eta}N,{pi}{pi}N,KY, {hor_ellipsis} reactions systematically, covering the wide energy and kinematic regions. The analysis is pursued with a dynamical coupled-channels (DCC) model, the EBAC-DCC model, within which the unitarity among relevant meson-baryon channels, including the three-body {pi}{pi}N channel, is fully taken into account.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

3D electrostatic gyrokinetic electron and fully kinetic ion simulation of lower-hybrid drift instability of Harris current sheet

The eigenmode stability properties of three-dimensional lower-hybrid-drift-instabilities (LHDI) in a Harris current sheet with a small but finite guide magnetic field have been systematically studied by employing the gyrokinetic electron and fully kinetic ion (GeFi) particle-in-cell (PIC) simulation model with a realistic ion-to-electron mass ratio m i /m e . In contrast to the fully kinetic PIC simulation scheme, the fast electron cyclotron motion and plasma oscillations are systematically removed in the GeFi model, and hence one can employ the realistic m i /m e . The GeFi simulations are benchmarked against and show excellent agreement with both the fully kinetic PIC simulation and the analytical eigenmode theory. Our studies indicate that, for small wavenumbers, ky, along the current direction, the most unstable eigenmodes are peaked at the location where $\vec{k}$• $\vec{B}$ =0, consistent with previous analytical and simulation studies. Here, $\vec{B}$ is the equilibrium magnetic field and $\vec{k}$ is the wavevector perpendicular to the nonuniformity direction. As ky increases, however, the most unstable eigenmodes are found to be peaked at $\vec{k}$ •$\vec{B}$ ≠0. Additionally, the simulation results indicate that varying m i /m e , the current sheet width, and the guide magnetic field can affect the stability of LHDI. Simulations with the varying mass ratio confirm the lower hybrid frequency and wave number scalings.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗