Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “INSULATION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Vacuum insulation of the high energy negative ion source for fusion application

Vacuum insulation on a large size negative ion accelerator with multiple extraction apertures and acceleration grids for fusion application was experimentally examined and designed. In the experiment, vacuum insulation characteristics were investigated in the JT-60 negative ion source with >1000 apertures on the grid with the surface area of {approx}2 m{sup 2}. The sustainable voltages varied with a square root of the gap lengths between the grids, and decreased with number of the apertures and with the surface area of the grids. Based on the obtained results, the JT-60SA (super advanced) negative ion source is designed to produce 22 A, 500 keV D{sup -} ion beams for 100 s.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials

Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10{sup -1} to 10{sup 5} Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Transport phenomena in intrinsic semiconductors and insulators at high current densities: Suppression of the broken neutrality drift

It is shown that, in addition to the diffusion and broken neutrality drift (BND) modes well-known for insulators and very lightly doped semiconductors, the quasineutral drift (QND) mode is possible. The transition from the BND to QND mode is accompanied by the appearance of a portion with a very sharp current rise in the current-voltage characteristic. This effect is observed in a new type of semiconductor detectors (CIDs, Current Injected Detectors) of high-intensity neutron and proton radiation, suggested, in particular, for Large Hadron Collider. The effect is unambiguously attributed now to the presence of radiation-induced deep centers in a semiconductor. It is shown, however, in this paper that the effect of a very sharp rise in current upon a slight increase in voltage is even possible when there are no deep centers. An equation adequately describing the possible transport modes in intrinsic semiconductors and insulators is derived. The results of an analytical study are confirmed by an adequate simulation.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Statistical analysis of the ion beam production in a self magnetically insulated diode

The paper presents the results of a study on shot to shot variation in energy density of an ion beam formed by a self-magnetically insulated diode with an explosive emission cathode. The experiments were carried out with the TEMP-4M accelerator operating in double-pulse mode: plasma formation occurs during the first pulse (negative polarity, 300–500 ns, 100–150 kV), and ion extraction and acceleration during the second pulse (positive polarity, 150 ns, 250–300 kV). Crucially, it was found that the standard deviation of energy density does not exceed 11%, whilst the same variation for ion current density was 20%–30%, suggesting the presence of neutrals in the beam. This idea is further supported by the fact that ion current density is only weakly dependant on the accelerating voltage and other output parameters of the accelerator (coefficient of determination < 0.3), whilst the correlation between the energy density of the beam and the output parameters is strong (coefficient of determination > 0.9). We attribute the neutral component as being due to charge exchange between accelerated ions and neutral molecules from a neutral layer near the anode surface. Implementation using a self-magnetically insulated diode with an explosive-emission cathode, having an operational lifetime of up to 10{sup 7} shots, has promising prospects for various technological applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Conductance modulation in topological insulator Bi{sub 2}Se{sub 3} thin films with ionic liquid gating

A Bi{sub 2}Se{sub 3} topological insulator field effect transistor is investigated by using ionic liquid as an electric double layer gating material, leading to a conductance modulation of 365% at room temperature. We discuss the role of charged impurities on the transport properties. The conductance modulation with gate bias is due to a change in the carrier concentration, whereas the temperature dependent conductance change is originated from a change in mobility. Large conductance modulation at room temperature along with the transparent optical properties makes topological insulators as an interesting (opto)electronic material.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Metal-insulator transition in SrTi{sub 1−x}V{sub x}O{sub 3} thin films

Epitaxial SrTi{sub 1−x}V{sub x}O{sub 3} (0 ≤ x ≤ 1) thin films were grown on (001)-oriented (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (LSAT) substrates using the pulsed electron-beam deposition technique. The transport study revealed a temperature driven metal-insulator transition (MIT) at 95 K for x = 0.67. The films with higher vanadium concentration (x > 0.67) were metallic corresponding to a Fermi liquid system. In the insulating phase (x < 0.67), the resistivity behavior was governed by Mott's variable range hopping mechanism. The possible mechanisms for the induced MIT are discussed, including the effects of electron correlation, lattice distortion, and Anderson localization.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Topological insulators in silicene: Quantum hall, quantum spin hall and quantum anomalous hall effects

Silicene is a monolayer of silicon atoms forming a two-dimensional honeycomb lattice, which shares almost every remarkable property with graphene. The low energy dynamics is described by Dirac electrons, but they are massive due to relatively large spin-orbit interactions. I will explain the following properties of silicene: 1) The band structure is controllable by applying an electric field. 2) Silicene undergoes a phase transition from a topological insulator to a band insulator by applying external electric field. 3) The topological phase transition can be detected experimentally by way of diamagnetism. 4) There is a novel valley-spin selection rules revealed by way of photon absorption. 5) Silicene yields a remarkably many phases such as quantum anomalous Hall phase and valley polarized metal when the exchange field is additionally introduced. 6) A silicon nanotubes can be used to convey spin currents under an electric field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Production and characterization of a composite insulation material from waste polyethylene teraphtalates

The pollution of polyethylene teraphtalate (PET) is in huge amounts due to the most widely usage as a packaging material in several industries. Regional pumice has several desirable characteristics such as porous structure, low-cost and light-weight. Considering the requirements approved by the Ministry of Public Works on isolation, composite insulation material consisting of PET and pumice was studied. Sheets of composites differing both in particle size of pumice and composition of polymer were produced by hot-molding technique. Characterization of new composite material was achieved by measuring its weight, density, flammability, endurance against both to common acids and bases, and to a force applied, heat insulation and water adsorption capacity. The results of the study showed that produced composite material is an alternative building material due to its desirable characteristics; low weight, capability of low heat conduction.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Measurements of the apparent thermal conductivity of multi-layer insulation between 20 K and 90 K

NASA has the need to efficiently store cryogenic propellants in space for long periods of time. One method to improve storage efficiency is to use multi-layer insulation (MLI), a technique that minimizes the boiling rate due to radiation heat transfer. Typically, the thermal performance of MLI is determined by measuring the rate of evaporation of liquid nitrogen from a calibrated cryostat. The main limitation with this method is that testing conditions are restricted by the boiling temperature of the LN{sub 2}, which may not match the requirements of the application. The Multi-Layer Insulation Thermal Conductivity Experiment (MIKE) at the National High Magnetic Field Laboratory is capable of measuring the effective thermal conductivity of MLI at variable boundary temperatures. MIKE uses cryo-refrigerators to control boundary temperatures in the calorimeter and a calibrated thermal link to measure the heat load. To make the measurements requested by NASA, MIKE needed to be recalibrated for the 20 K to 90 K range. Also, due to the expectation of a lower heat transfer rate, the heat load support rod material was changed to one with a lower thermal conductivity to ensure the temperature difference seen on the cold rod could be measurable at the estimated heat load. Presented are the alterations to MIKE including calibration data and heat load measurements on new load-bearing MLI supplied by NASA.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Non-destructive qualification tests for ITER cryogenic axial insulating breaks

In the ITER superconducting magnets the dielectric separation between the CICC (Cable-In-Conduit Conductors) and the helium supply pipes is made through the so-called insulating breaks (IB). These devices shall provide the required dielectric insulation at a 30 kV level under different types of stresses and constraints: thermal, mechanical, dielectric and ionizing radiations. As part of the R and D program, the ITER Organization launched contracts with industrial companies aimed at the qualification of the manufacturing techniques. After reviewing the main functional aspects, this paper describes and discusses the protocol established for non-destructive qualification tests of the prototypes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Enhancement in the transport critical current density J{sub c} in YBa{sub 2}Cu{sub 3}O{sub 7−δ} added with an insulating nano crystalline YBa{sub 2}HfO{sub 5.5} perovskite

When a magnetic field is applied to type II superconductors, such as YBa{sub 2}Cu{sub 3}0{sub 7−δ} (YBCO), the flux quanta penetrate the material as a regular array of vortices. However when transport currents are applied, they act to move these vortices, thus lowers the critical current density (J{sub c}) as well as destroying superconductivity. The development of microstructures made of YBCO materials has enabled engineers to increase the critical current density, within Type II materials by introducing flux pinning centres into the material. The microstructure and flux pinning properties of YBa{sub 2}Cu{sub 3}O{sub 7−δ} system with varying levels (0-5 wt. %) of a nano perovskite ceramic insulator; YBa{sub 2}HfO{sub 5.5} addition was studied in detail. Orthorhombic YBa{sub 2}Cu{sub 3}O{sub 7−δ} powder was prepared through conventional solid state route and a modified combustion method was used for synthesizing nanocrystalline YBa{sub 2}HfO{sub 5.5}. The structure and microstructure of the samples examined by X-ray diffraction and scanning electron microscopy showed that YBa{sub 2}HfO{sub 5.5} and YBCO remained unreacted even at higher processing temperature without deteriorating the superconducting properties. The scanning electron microscope image shows that YBa{sub 2}HfO{sub 5.5} forms an electrical-network between grains. These observations suggest that the YBa{sub 2}HfO{sub 5.5} addition to the Y-123-compounds improve the electrical connection between superconducting grains and substantial improvements in the relative electrical transport properties of the composites. The variation of sintering temperature, density, critical transition temperature (T{sub c}) and magnetic field dependence of critical current density (J{sub c}) of YBa{sub 2}Cu{sub 3}O{sub 7−δ} having different proportions of YBa{sub 2}HfO{sub 5.5} in the matrix were also studied in detail. It is found that the addition of these elements considerably enhances the flux pinning strength of the system, and there is also an increase of critical temperature (T{sub c}) and critical current density (J{sub c}) up to an optimum value of 8.76 × 10{sup 4} A/cm{sup 2} for a concentration of 2 wt % addition of nano YBa{sub 2}HfO{sub 5.5}. The enhancement of the critical current density in the YBa{sub 2}Cu{sub 3}O{sub 7−δ} - YBa{sub 2}HfO{sub 5.5} samples is attributed to the sustained formation of the insulating and non-reacting YBa{sub 2}HfO{sub 5.5} phase acting as pinning center. The addition of YBa{sub 2}HfO{sub 5.5} in YBa{sub 2}Cu{sub 3}O{sub 7−δ} bulk superconductor also enhances the pinning force density from 3 ×10{sup 6} N/m{sup 3} to 69.6 × 10{sup 6}N/m{sup 3} at 77 K.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Calculation of metallic and insulating phases of V{sub 2}O{sub 3} by hybrid density functionals

The electronic structure of vanadium sesquioxide V{sub 2}O{sub 3} in its different phases has been calculated using the screened exchange hybrid density functional. The hybrid functional accurately reproduces the experimental electronic properties of all three phases, the paramagnetic metal (PM) phase, the anti-ferromagnetic insulating phase, and the Cr-doped paramagnetic insulating (PI) phase. We find that a fully relaxed supercell model of the Cr-doped PI phase based on the corundum structure has a monoclinic-like local strain around the substitutional Cr atoms. This is found to drive the PI-PM transition, consistent with a Peierls-Mott transition. The PI phase has a calculated band gap of 0.15 eV, in good agreement with experiment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Status of surface conduction in topological insulators

In this report, we scrutinize the thickness dependent resistivity data from the recent literature on electrical transport measurements in topological insulators. A linear increase in resistivity with increase in thickness is expected in the case of these materials since they have an insulating bulk and a conducting surface. However, such a trend is not seen in the resistivity versus thickness data for all the cases examined, except for some samples, where it holds for a range of thickness.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Note: Long-range scanning tunneling microscope for the study of nanostructures on insulating substrates

The scanning tunneling microscope (STM) is a powerful tool for studying the electronic properties at the atomic level, however, it is of relatively small scanning range and the fact that it can only operate on conducting samples prevents its application to study heterogeneous samples consisting of conducting and insulating regions. Here we present a long-range scanning tunneling microscope capable of detecting conducting micro and nanostructures on insulating substrates using a technique based on the capacitance between the tip and the sample and performing STM studies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Optimization of the Jastrow factor using the random-phase approximation and a similarity-transformed Hamiltonian: Application to band-structure calculation for some semiconductors and insulators

Based on the random-phase approximation and the transcorrelated (TC) method, we optimize the Jastrow factor together with one-electron orbitals in the Slater determinant in the correlated wave function with a new scheme for periodic systems. The TC method is one of the promising wave function theories for first-principles electronic structure calculation, where the many-body wave function is approximated as a product of a Slater determinant and a Jastrow factor, and the Hamiltonian is similarity-transformed by the Jastrow factor. Using this similarity-transformed Hamiltonian, we can optimize the one-electron orbitals without evaluating 3N-dimensional integrations for the N-electron system. In contrast, optimization of the Jastrow factor within the framework of the TC method is computationally much more expensive and has not been performed for solid-state calculations before. In this study, we also benefit from the similarity-transformation in optimizing the Jastrow factor. Our optimization scheme is tested in applications to some solids from narrow-gap semiconductors to wide-gap insulators, and it is verified that the band gap of a wide-gap insulator and the lattice constants of some solids are improved by this optimization with reasonable computational cost.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Evidence of the metal-insulator transition in ultrathin unstrained V{sub 2}O{sub 3} thin films

We report the strain state and transport properties of V{sub 2}O{sub 3} layers and V{sub 2}O{sub 3}/Cr{sub 2}O{sub 3} bilayers deposited by molecular beam epitaxy on (0001)-Al{sub 2}O{sub 3}. By changing the layer on top of which V{sub 2}O{sub 3} is grown, we change the lattice parameters of ultrathin V{sub 2}O{sub 3} films significantly. We find that the metal-insulator transition is strongly attenuated in ultrathin V{sub 2}O{sub 3} layers grown coherently on Al{sub 2}O{sub 3}. This is in contrast with ultrathin V{sub 2}O{sub 3} layers grown on Cr{sub 2}O{sub 3} buffer layers, where the metal-insulator transition is preserved. Our results provide evidence that the existence of the transition in ultrathin films is closely linked with the lattice deformation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Superconducting tantalum nitride-based normal metal-insulator-superconductor tunnel junctions

We report the development of superconducting tantalum nitride (TaN{sub x}) normal metal-insulator-superconductor (NIS) tunnel junctions. For the insulating barrier, we used both AlO{sub x} and TaO{sub x} (Cu-AlO{sub x}-Al-TaN{sub x} and Cu-TaO{sub x}-TaN{sub x}), with both devices exhibiting temperature dependent current-voltage characteristics which follow the simple one-particle tunneling model. The superconducting gap follows a BCS type temperature dependence, rendering these devices suitable for sensitive thermometry and bolometry from the superconducting transition temperature T{sub C} of the TaN{sub x} film at ∼5 K down to ∼0.5 K. Numerical simulations were also performed to predict how junction parameters should be tuned to achieve electronic cooling at temperatures above 1 K.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Quantum phenomena in transport measurements of topological insulator nanostructures (Review Article)

We review the recent experimental advances on quantum phenomena in transport measurements of topological insulators with emphasis on quantum oscillation, weak antilocalization and Aharonov-Bohm effect and Altshuler-Aronov-Spivak effect. Following a brief introduction on the topic, we discuss the identification of the topological surface state based on quantum phenomena. Research prospect of topological insulators is described at the end of this article.

Fang, Lei↗