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DOE OSTI2011

The many faces of shear Alfven waves

One of the fundamental waves in magnetized plasmas is the shear Alfven wave. This wave is responsible for rearranging current systems and, in fact all low frequency currents in magnetized plasmas are shear waves. It has become apparent that Alfven waves are important in a wide variety of physical environments. Shear waves of various forms have been a topic of experimental research for more than fifteen years in the large plasma device (LAPD) at UCLA. The waves were first studied in both the kinetic and inertial regimes when excited by fluctuating currents with transverse dimension on the order of the collisionless skin depth. Theory and experiment on wave propagation in these regimes is presented, and the morphology of the wave is illustrated to be dependent on the generation mechanism. Three-dimensional currents associated with the waves have been mapped. The ion motion, which closes the current across the magnetic field, has been studied using laser induced fluorescence. The wave propagation in inhomogeneous magnetic fields and density gradients is presented as well as effects of collisions and reflections from boundaries. Reflections may result in Alfvenic field line resonances and in the right conditions maser action. The waves occur spontaneously on temperature and density gradients as hybrids with drift waves. These have been seen to affect cross-field heat and plasma transport. Although the waves are easily launched with antennas, they may also be generated by secondary processes, such as Cherenkov radiation. This is the case when intense shear Alfven waves in a background magnetoplasma are produced by an exploding laser-produced plasma. Time varying magnetic flux ropes can be considered to be low frequency shear waves. Studies of the interaction of multiple ropes and the link between magnetic field line reconnection and rope dynamics are revealed. This manuscript gives us an overview of the major results from these experiments and provides a modern prospective for the earlier studies of shear Alfven waves.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2011

Direct Synthesis of Fe-Pt Nanoparticles in Ordered Face Centered (fct)LI{sub o} Phase by Microwave Assisted Route

In the present work, microwave-assisted chemical reduction route has been explored for the direct synthesis of fct LIo-phase of Fe-Pt nanoparticles. Effects of microwave power and irradiation time on the growth process were investigated. Using this facile and high yield technique we could tune particle size from 7 to 17 nm. The as-prepared FePt were found to be sensitive to the microwave irradiation power, while influence of exposure time was insignificant. The hysteresis measurements were performed at room temperature (300 K) to study magnetic properties of as-synthesized Fe-Pt as a function of crystallize size. The coercivity and saturation magnetization was observed to be decrease with diminishing for direct synthesis of metal alloys.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Polycrystalline iron nitride films fabricated by reactive facing-target sputtering: Structure, magnetic and electrical transport properties

Structure, magnetic and electrical transport properties of the reactive sputtered iron nitride films fabricated at different substrate temperatures (T{sub s}) and nitrogen flow rates (F{sub N{sub 2}}) were investigated systematically. The single-phase polycrystalline {gamma}'-Fe{sub 4}N film was obtained at F{sub N{sub 2}} = 20 sccm and T{sub s} = 450 deg. C. The films are soft ferromagnetic at room temperature. The electrical resistivity ({rho}) of the films fabricated at different F{sub N{sub 2}} and T{sub s} decreases with the decreasing temperature, showing a metallic behavior. Meanwhile, a variety of magnetoresistance (MR) behaviors were observed depending on the applied magnetic field and measuring temperature. It can be deduced that the complex MR behaviors are dominated by Lorentz force, spin-orbit interaction, and weak localization effect.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Compact steady-state and high-flux Falcon ion source for tests of plasma-facing materials

This paper describes the design and operation of the Falcon ion source. It is based on conventional design of anode layer thrusters. This ion source is a versatile, compact, affordable, and highly functional in the research field of the fusion materials. The reversed magnetic field configuration of the source allows precise focusing of the ion beam into small spot of Almost-Equal-To 3 mm and also provides the limited capabilities for impurity mass-separation. As the result, the source generates steady-state ion beam, which irradiates surface with high heat (0.3 - 21 MW m{sup -2}) and particle fluxes (4 Multiplication-Sign 10{sup 21}- 3 Multiplication-Sign 10{sup 23} m{sup -2}s{sup -1}), which approaches the upper limit for the flux range expected in ITER.

43 PARTICLE ACCELERATORS↗

DOE OSTI2013

Effect of Ti seed layers on structure of self-organized epitaxial face-centered-cubic-Ag(001) oriented nanodots

The influence of Ti seed layers on the structure of self-organized Ag nanodots, obtained with a Ti seed-layer-assisted thermal agglomeration method, has been investigated. The samples were grown on MgO(001) single crystal substrates by RF magnetron sputter deposition. The samples were deposited at room temperature and post-annealed at 350 °C for 4 h while maintaining the chamber vacuum conditions. The results of atomic force microscopy (AFM) observations indicated that the insertion of the Ti seed layer (0.6–5.0 nm) between the MgO substrate and Ag layer promotes the agglomeration process, forming the nanodot array. Comparisons between the AFM images revealed that the size of the Ag nanodots was increased with an increase in the Ti seed layer thickness. The atomic concentration of the film surface was confirmed by X-ray photoelectron spectroscopy (XPS). The XPS result suggested that the nanodot surface mainly consisted of Ag. Moreover, X-ray diffraction results proved that the initial deposition of the Ti seed layer (0.6–5.0 nm) onto MgO(001) prior to the Ag deposition yielded high-quality fcc-Ag(001) oriented epitaxial nanodots. The optical absorbance spectra of the fabricated Ag nanodots with various Ti seed layer thicknesses were obtained in the visible light range.

36 MATERIALS SCIENCE↗

DOE OSTI2014

High spatial resolution mapping of deposition layers on plasma facing materials by laser ablation microprobe time-of-flight mass spectroscopy

A laser ablation microprobe time-of-flight mass spectroscopy (LAM-TOF-MS) system with high spatial resolution, ∼20 nm in depth and ∼500 μm or better on the surface, is developed to analyze the composition distributions of deposition layers on the first wall materials or first mirrors in tokamak. The LAM-TOF-MS system consists of a laser ablation microprobe combined with a TOF-MS and a data acquisition system based on a LabVIEW program software package. Laser induced ablation combined with TOF-MS is an attractive method to analyze the depth profile of deposited layer with successive laser shots, therefore, it can provide information for composition reconstruction of the plasma wall interaction process. In this work, we demonstrate that the LAM-TOF-MS system is capable of characterizing the depth profile as well as mapping 2D composition of deposited film on the molybdenum first mirror retrieved from HL-2A tokamak, with particular emphasis on some of the species produced during the ablation process. The presented LAM-TOF-MS system provides not only the 3D characterization of deposition but also the removal efficiency of species of concern.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2014

Thermal plasma processed ferro-magnetically ordered face-centered cubic iron at room temperature

Here, we report tailor made phase of iron nanoparticles using homogeneous gas phase condensation process via thermal plasma route. It was observed that crystal lattice of nano-crystalline iron changes as a function of operating parameters of the plasma reactor. In the present investigation iron nanoparticles have been synthesized in presence of argon at operating pressures of 125–1000 Torr and fixed plasma input DC power of 6 kW. It was possible to obtain pure fcc, pure bcc as well as the mixed phases for iron nanoparticles in powder form as a function of operating pressure. The as synthesized product was characterized for understanding the structural and magnetic properties by using X-ray diffraction, vibrating sample magnetometer, and Mössbauer spectroscopy. The data reveal that fcc phase is ferromagnetically ordered with high spin state, which is unusual whereas bcc phase is found to be ferromagnetic as usual. Finally, the structural and magnetic properties are co-related.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Symmetry remnants in the face of competing interactions in nuclei

Detailed description of nuclei necessitates model Hamiltonians which break most dynamical symmetries. Nevertheless, generalized notions of partial and quasi dynamical symmetries may still be applicable to selected subsets of states, amidst a complicated environment of other states. We examine such scenarios in the context of nuclear shape-phase transitions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Quantitative analysis of Indonesia’s reserves and energy security as an evaluation by the nation in facing global competition

Energy security has become a serious concern for all countries in the world and each country has its own definiton for measuring its energy security. The objective of this study was to measure energy security of Indonesia quantitatively by comparing it with other countries and provide some recommendations for enhancing the energy security. In this study, the database was developed from various sources and was cross-checked to confirm validity of the data. Then the parameters of energy security were defined, where all of data will be processed towards the selected parameters. These parameters (e.g. Primary Energy mix, TPES/capita, FEC/capita, Self Sufficiency, Refining capacity, Overseas Energy Resources, Resources diversification) are the standards used to produce an analysis or evaluation of national energy management. Energy balances for Indonesia and 10 selected countries (USA, Germany, Russia, England, Japan, China, South Korea, Singapore, Thailand and India) were presented from 2009 to 2013. With a base index of 1.0 for Indonesia, calculated energy security index capable of representing Indonesia energy security compared relatively to other countries were also presented and discussed in detail. In 2012, Indonesia security index is ranked 11 from 11 countries, while USA and South Korea are the highest with security index of 3.36 and 2.89, respectively. According to prediction for 2025, Indonesia energy security is ranked 10 from 11 countries with only Thailand has lower security index (0.98). This result shows that Indonesia energy security was vulnerable to crisis and must be improved. Therefore this study proposed some recommendations to improve Indonesia energy security. Indonesia need to increase oil production by constructing new refinery plants, developing infrastructure for energy distribution to reduce the potential of energy shortage and accelerating the utilization of renewable energy to reduce the excessive use of primary energy. From energy policy proposed in this study, Indonesia energy security for 2025 could be improved to ranked 8 of 11 countries, better than Malaysia, Thailand and Singapore.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2016

Unraveling wall conditioning effects on plasma facing components in NSTX-U with the Materials Analysis Particle Probe (MAPP)

A novel PFC diagnostic, the Materials Analysis Particle Probe (MAPP), has been recently commissioned in the National Spherical Torus Experiment Upgrade (NSTX-U). MAPP is currently monitoring the chemical evolution of the PFCs in the NSTX-U lower divertor at 107 cm from the tokamak axis on a day-to-day basis. Here in this work, we summarize the methodology that was adopted to obtain qualitative and quantitative descriptions of the samples chemistry. Using this methodology, we were able to describe all the features in all our spectra to within a standard deviation of ±0.22 eV in position and ±248 s -1 eV in area. Additionally, we provide an example of this methodology with data of boronized ATJ graphite exposed to NSTX-U plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2017

Compatibility of lithium plasma-facing surfaces with high edge temperatures in the Lithium Tokamak Experiment

We measured high edge electron temperatures (200 eV or greater) at the wall-limited plasma boundary in the Lithium Tokamak Experiment (LTX). Flat electron temperature profiles are a long-predicted consequence of low recycling boundary conditions. Plasma density in the outer scrape-off layer is very low, 2-3 x 10(17) m(-3), consistent with a low recycling metallic lithium boundary. In spite of the high edge temperature, the core impurity content is low. Z(eff) is estimated to be similar to 1.2, with a very modest contribution (< 0.1) from lithium. Experiments are transient. Gas puffing is used to increase the plasma density. After gas injection stops, the discharge density is allowed to drop, and the edge is pumped by the low recycling lithium wall. An upgrade to LTX-LTX-beta, which includes a 35A, 20 kV neutral beam injector (on loan to LTX from Tri-Alpha Energy) to provide core fueling to maintain constant density, as well as auxiliary heating, is underway. LTX-beta is briefly described.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2019

Time-resolved laser-induced desorption spectroscopy (LIDS) for quantified in-situ hydrogen isotope retention measurement and removal from plasma facing materials

A laboratory scale laser induced thermal desorption spectroscopy system is developed and tested on tungsten-deuterium and titanium-deuterium codeposits, and its feasibility as a hydrogenic inventory measurement diagnostic is demonstrated over a range of retention values from 5 × 10 19 m -2 to 7 × 10 23 m -2 for absorbed laser power densities as low as 8 MW m -2 . Codeposit layer samples are grown by magnetron sputtering and immersed in a weak argon rf plasma. A 1 kW fiber laser (λ = 1100 nm) heats the samples up to a peak surface temperature ranging from 900 to 1500 K using pulse widths of 0.5 and 1 s. Spectral line emission from Balmer series Dα and Hα from thermally desorbed deuterium and hydrogen, as well as line emission from argon, are monitored as a function of time using an optical spectrometer with maximum temporal resolution of 1 ms. To correct for wall recycling and pumping speed, and to accurately measure the time evolution of the laser-induced thermal desorption, the raw Dα signal is deconvolved with the system response function, which is obtained by injecting a short burst of D 2 to approximate an impulse. Calibration is done with a standard D 2 leak, and laser induced desorption spectroscopy deuterium retention values are found to be in good agreement with companion measurements made using conventional temperature programmed desorption on samples from the same codeposit batch.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Machine learned interatomic potential for dispersion strengthened plasma facing components

Tungsten (W) is a material of choice for the divertor material due to its high melting temperature, thermal conductivity, and sputtering threshold. However, W has a very high brittle-to-ductile transition temperature, and at fusion reactor temperatures (≥1000 K), it may undergo recrystallization and grain growth. Dispersion-strengthening W with zirconium carbide (ZrC) can improve ductility and limit grain growth, but much of the effects of the dispersoids on microstructural evolution and thermomechanical properties at high temperatures are still unknown. We present a machine learned Spectral Neighbor Analysis Potential for W–ZrC that can now be used to study these materials. In order to construct a potential suitable for large-scale atomistic simulations at fusion reactor temperatures, it is necessary to train on ab initio data generated for a diverse set of structures, chemical environments, and temperatures. Further accuracy and stability tests of the potential were achieved using objective functions for both material properties and high temperature stability. Additionally, validation of lattice parameters, surface energies, bulk moduli, and thermal expansion is confirmed on the optimized potential. Tensile tests of W/ZrC bicrystals show that although the W(110)–ZrC(111) C-terminated bicrystal has the highest ultimate tensile strength (UTS) at room temperature, observed strength decreases with increasing temperature. At 2500 K, the terminating C layer diffuses into the W, resulting in a weaker W–Zr interface. Meanwhile, the W(110)–ZrC(111) Zr-terminated bicrystal has the highest UTS at 2500 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2012

Structural and functional analysis of an essential nucleoporin heterotrimer on the cytoplasmic face of the nuclear pore complex

So far, only a few of the interactions between the {approx}30 nucleoporins comprising the modular structure of the nuclear pore complex have been defined at atomic resolution. Here we report the crystal structure, at 2.6 {angstrom} resolution, of a heterotrimeric complex, composed of fragments of three cytoplasmically oriented nucleoporins of yeast: Nup82, Nup116, and Nup159. Our data show that the Nup82 fragment, representing more than the N-terminal half of the molecule, folds into an extensively decorated, seven-bladed {beta}-propeller that forms the centerpiece of this heterotrimeric complex and anchors both a C-terminal fragment of Nup116 and the C-terminal tail of Nup159. Binding between Nup116 and Nup82 is mutually reinforced via two loops, one emanating from the Nup82 {beta}-propeller and the other one from the {beta}-sandwich fold of Nup116, each contacting binding pockets in their counterparts. The Nup82-Nup159 interaction occurs through an amphipathic {alpha}-helix of Nup159, which is cradled in a large hydrophobic groove that is generated from several large surface decorations of the Nup82 {beta}-propeller. Although Nup159 and Nup116 fragments bind to the Nup82 {beta}-propeller in close vicinity, there are no direct contacts between them, consistent with the noncooperative binding that was detected biochemically. Extensive mutagenesis delineated hot-spot residues for these interactions. We also showed that the Nup82 {beta}-propeller binds to other yeast Nup116 family members, Nup145N, Nup100 and to the mammalian homolog, Nup98. Notably, each of the three nucleoporins contains additional nuclear pore complex binding sites, distinct from those that were defined here in the heterotrimeric Nup82 {center_dot} Nup159 {center_dot} Nup116 complex.

36 MATERIALS SCIENCE↗

DOE OSTI2019