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At least 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Investigation of the ignition processes of a multi-injection flame in a Diesel engine environment using the flamelet model

In this paper, the first flamelet analysis is conducted of a highly resolved DNS of a multi-injection flame with both auto-ignition and ignition induced by flame-flame interaction. A novel method is proposed to identify the different combustion modes of ignition processes using generalized flamelet equations. The state-of-the-art DNS database generated by Rieth et al. (US National Combustion Meeting, 2019) for a multi-injection flame in a Diesel engine environment is investigated. Three-dimensional flamelets are extracted from the DNS at different time instants with a focus on auto-ignition and interaction-ignition processes. The influences of mixture field interactions and the scalar dissipation rate on the ignition process are investigated by varying the species composition boundary conditions of the transient flamelet equations. Budget analyses of the generalized flamelet equations show that the transport along the mixture fraction iso-surface is insignificant during the auto-ignition process, but becomes important when interaction-ignition occurs, which is further confirmed through a flamelet regime classification method.

42 ENGINEERING↗
DOE OSTI2024

Enhanced passivation and stability of negative charge injected SiN x with higher nitrogen content on the boron diffused surface of n-type Si solar cells

This paper explores the potential of the negatively charged SiN x using plasma charge injection technology to passivate the front textured boron-diffused emitter of n-type Si solar cells. The high-x value single SiN x layer with x ≥ 1.30 (x = N/Si) previously developed for the planarized rear-side passivation of p-type silicon solar cells, with an excellent passivation and charge stability, was found to be unacceptable for the passivation on the front textured boron emitter of n-type cells due to a severe bulk lifetime degradation issue. Therefore, in this study, we investigated a new concept of depositing a dual-x SiN x with a low-x SiN x layer (x~1.01) on top of a high-x SiN x layer (x~1.30) for passivation of the front textured rough surface of boron diffused emitter in n-type cells. Here, the optimized dual-x SiN x stack reveals the promise of charge retention for more than 25 years in field operation as well as excellent passivation of boron-doped emitter without bulk lifetime degradation. N-type cells with the optimized dual-x SiN x after charge injection show comparable cell performance to Al 2 O 3 passivated reference cells. The results of cell-level light stability tests using one-cell minimodules exhibit cell performance decay characteristics similar to the traditional Al 2 O 3 /SiN x passivated reference module.

14 SOLAR ENERGY↗
DOE OSTI2011

Effect of Self-Assembled Monolayers on Charge Injection and Transport in Poly(3-hexylthiophene)-Based Field-Effect Transistors at Different Channel Length Scales

Charge injection and transport in bottom-contact regioregular-poly(3-hexylthiophene) (rr-P3HT) based field-effect transistors (FETs), wherein the Au source and drain contacts are modified by self-assembled monolayers (SAMs), is reported at different channel length scales. Ultraviolet photoelectron spectroscopy is used to measure the change in metal work function upon treatment with four SAMs consisting of thiol-absorbates of different chemical composition. Treatment of FETs with electron-poor (electron-rich) SAMs resulted in an increase (decrease) in contact metal work function because of the electron-withdrawing(-donating) tendency of the polar molecules. The change in metal work function affects charge injection and is reflected in the form of the modulation of the contact resistance, RC. For example, RC decreased to 0.18 MΩ in the case of the (electron-poor) 3,5-bis-trifluoromethylbenzenethiol treated contacts from the value of 0.61 MΩ measured in the case of clean Au-contacts; whereas it increased to 0.97 MΩ in the case of the (electron-rich) 3-thiomethylthiophene treated contacts. Field-effect mobility values are observed to be affected in short-channel devices (< 20 m) but not in long-channel devices. This channel length dependent behavior of mobility is attributed to grain-boundary limited charge transport at longer channel lengths in these devices.

3-hexylthiophene↗
DOE OSTI2021

Potential Link Between 2020 Mentone, West Texas M5 Earthquake and Nearby Wastewater Injection: Implications for Aquifer Mechanical Properties

Abstract The M5 Mentone earthquake that occurred on March 26, 2020, was the largest event recorded over the last 2 decades in West Texas within the Delaware Basin, a U.S. major petroleum‐producing area. Also, numerous hydrofracturing and wastewater disposal wells are spread across this region. Within a 30 km distance to mainshock, eight class‐II injection wells for industrial wastewater disposal target the deep porous Ellenburger aquifer at an average rate of 1.36 × 10 6 barrel (BBL) per month during 2012–2020. Poroelastic models of fluid diffusion show these nearby injectors collectively imparted up to 80.5 kPa of Coulomb stress at the mainshock location, capable of triggering this M5 event. Assuming the Mentone event occurs when pore‐pressure increase is maximum, the time delay between peak injection and the M5 occurrence corresponds with an optimal permeability of 6.76 × 10 ‐14 m 2 for the Ellenburger aquifer layer, in agreement with independent estimates.

15 GEOTHERMAL ENERGY↗
DOE OSTI2023

Potential Non-Linearities in the High Latitude Circulation and Ozone Response to Stratospheric Aerosol Injection

The impacts of Stratospheric Aerosol Injection (SAI) on the atmosphere and surface climate depend on when and where the sulfate aerosol precursors are injected, as well as on how much surface cooling is to be achieved. We use a set of CESM2(WACCM6) SAI simulations achieving three different levels of global mean surface cooling and demonstrate that unlike some direct surface climate impacts driven by the reflection of solar radiation by sulfate aerosols, the SAI-induced changes in the high latitude circulation and ozone are more complex and could be non-linear. This manifests in our simulations by disproportionally larger Antarctic springtime ozone loss, significantly larger intra-ensemble spread of the Arctic stratospheric jet and ozone responses, and non-linear impacts on the extratropical modes of surface climate variability under the strongest-cooling SAI scenario compared to the weakest one. These potential non-linearities may add to uncertainties in projections of regional surface impacts under SAI.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

An injectable acoustic transmitter for juvenile salmon

Salmon recovery, and the potential detrimental effects of dams on fish, has been attracting national attention in due to great environmental and economic implications. Acoustic Telemetry has been the primary method for studying salmon passage. However, the size of the existing transmitters limits the minimum size of fish that can be studied, introducing bias to the study results. We developed the first acoustic fish transmitter that can be implanted by injection instead of surgery. The new injectable transmitter offers improved performance and 30% weight reduction. Because the new transmitter costs significantly less to use, substantially reduces adverse effects of implantation, and provides additional biological benefits for tagged fish, it will become the enabling technology for studying migration behavior and survival of species and sizes of fish that have never been studied before. This will lead to critical information for salmon recovery and the development of fish-friendly hydroelectric systems.

42 ENGINEERING↗
DOE OSTI2012

New ion source for KSTAR neutral beam injection system

The neutral beam injection system (NBI-1) of the KSTAR tokamak can accommodate three ion sources; however, it is currently equipped with only one prototype ion source. In the 2010 and 2011 KSTAR campaigns, this ion source supplied deuterium neutral beam power of 0.7-1.6 MW to the KSTAR plasma with a beam energy of 70-100 keV. A new ion source will be prepared for the 2012 KSTAR campaign with a much advanced performance compared with the previous one. The newly designed ion source has a very large transparency ({approx}56%) without deteriorating the beam optics, which is designed to deliver a 2 MW injection power of deuterium beams at 100 keV. The plasma generator of the ion source is of a horizontally cusped bucket type, and the whole inner wall, except the cathode filaments and plasma grid side, functions as an anode. The accelerator assembly consists of four multi-circular aperture grids made of copper and four electrode flanges made of aluminum alloy. The electrodes are insulated using PEEK. The ion source will be completed and tested in 2011.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Multifunctional bulk plasma source based on discharge with electron injection

A bulk plasma source, based on a high-current dc glow discharge with electron injection, is described. Electron injection and some special design features of the plasma arc emitter provide a plasma source with very long periods between maintenance down-times and a long overall lifetime. The source uses a sectioned sputter-electrode array with six individual sputter targets, each of which can be independently biased. This discharge assembly configuration provides multifunctional operation, including plasma generation from different gases (argon, nitrogen, oxygen, acetylene) and deposition of composite metal nitride and oxide coatings.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Experimental and computational study of the injection of antiprotons into a positron plasma for antihydrogen production

One of the goals of synthesizing and trapping antihydrogen is to study the validity of charge-parity-time symmetry through precision spectroscopy on the anti-atoms, but the trapping yield achieved in recent experiments must be significantly improved before this can be realized. Antihydrogen atoms are commonly produced by mixing antiprotons and positrons stored in a nested Penning-Malmberg trap, which was achieved in ALPHA by an autoresonant excitation of the antiprotons, injecting them into the positron plasma. In this work, a hybrid numerical model is developed to simulate antiproton and positron dynamics during the mixing process. The simulation is benchmarked against other numerical and analytic models, as well as experimental measurements. The autoresonant injection scheme and an alternative scheme are compared numerically over a range of plasma parameters which can be reached in current and upcoming antihydrogen experiments, and the latter scheme is seen to offer significant improvement in trapping yield as the number of available antiprotons increases.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Impurity mixing and radiation asymmetry in massive gas injection simulations of DIII-D

Simulations of neon massive gas injection into DIII-D are performed with the 3D MHD code NIMROD. The poloidal and toroidal distribution of the impurity source is varied. This report will focus on the effects of the source variation on impurity mixing and radiated power asymmetry. Even toroidally symmetric impurity injection is found to produce asymmetric radiated power due to asymmetric convective heat flux produced by the 1/1 mode. When the gas source is toroidally localized, the phase relationship between the mode and the source location is important, affecting both radiation peaking and impurity mixing. Under certain circumstances, a single, localized gas jet could produce better radiation symmetry during the disruption thermal quench than evenly distributed impurities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Induction of electron injection and betatron oscillation in a plasma-waveguide-based laser wakefield accelerator by modification of waveguide structure

By adding a transverse heater pulse into the axicon ignitor-heater scheme for producing a plasma waveguide, a variable three-dimensionally structured plasma waveguide can be fabricated. With this technique, electron injection in a plasma-waveguide-based laser wakefield accelerator was achieved and resulted in production of a quasi-monoenergetic electron beam. The injection was correlated with a section of expanding cross-section in the plasma waveguide. Moreover, the intensity of the X-ray beam produced by the electron bunch in betatron oscillation was greatly enhanced with a transversely shifted section in the plasma waveguide. The technique opens a route to a compact hard-X-ray pulse source.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

A simple scheme for injection and extraction in compact rings

There has been great interest in building compact synchrotrons for various applications, for example, inverse Compton scattering X-ray sources. However, the beam injection and extraction in compact rings require careful design for the lack of space. In this paper, we propose a simple combined injection-extraction scheme exploiting the fringe field of existing dipole magnets instead of additional septum magnets. This scheme is illustrated by using the 4.8 m ring proposed for Tsinghua Thomson scattering X-ray source as an example. Particle tracking is applied to demonstrate the validity of this scheme.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Scattering assisted injection based injectorless mid infrared quantum cascade laser

An injectorless five-well mid infrared quantum cascade laser is analyzed which relies on phonon scattering injection in contrast to resonant tunneling injection, which has been previously used for injectorless designs. A Monte Carlo based self-consistent electron and photon transport simulator is used to analyze the performance of the analyzed design and compare it to existing injectorless designs. The simulation results show that the analyzed design could greatly enhance the optical gain and the characteristic temperatures of injectorless quantum cascade lasers (QCLs) which have typically been hindered by low characteristic temperatures and significant temperature related performance degradation. Simulations of the analyzed device predict threshold current densities of 0.85 kA/cm{sup 2} and 1.95 kA/cm{sup 2} at 77 K and 300 K, respectively, which are comparable to the threshold current densities of conventional injector based QCLs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Electric field effects on spin accumulation in Nb-doped SrTiO{sub 3} using tunable spin injection contacts at room temperature

We report on features in charge transport and spin injection in an oxide semiconductor, Nb-doped SrTiO{sub 3}. This is demonstrated using electrically tunable spin injection contacts which exploit the large electric field at the interface and its interplay with the relative permittivity of the semiconductor. We realize spin accumulation in Nb-doped SrTiO{sub 3} which displays a unique dependence of the spin lifetime with bias polarity. These findings suggest a strong influence of the interface electric field on the charge transport as well as on spin accumulation unlike in conventional semiconductors and opens up promising avenues in oxide spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Injection and acceleration of electron bunch in a plasma wakefield produced by a chirped laser pulse

An ultrashort laser pulse propagating in plasma can excite a nonlinear plasma wakefield which can trap and accelerate charged particles up to GeV. One-dimensional analysis of electron injection, trapping, and acceleration by different chirped pulses propagating in plasma is investigated numerically. In this paper, we inject electron bunches in front of the chirped pulses. It is indicated that periodical chirped laser pulse can trap electrons earlier than other pulses. It is shown that periodical chirped laser pulses lead to decrease the minimum momentum necessary to trap the electrons. This is due to the fact that periodical chirped laser pulses are globally much efficient than nonchirped pulses in the wakefield generation. It is found that chirped laser pulses could lead to much larger electron energy than that of nonchirped pulses. Relative energy spread has a lower value in the case of periodical chirped laser pulses.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Polarization self-screening in [0001] oriented InGaN/GaN light-emitting diodes for improving the electron injection efficiency

InGaN/GaN light-emitting diodes (LEDs) grown along the [0001] orientation inherit very strong polarization induced electric fields. This results in a reduced effective conduction band barrier height for the p-type AlGaN electron blocking layer (EBL) and makes the electron blocking effect relatively ineffective and the electron injection efficiency drops. Here, we show the concept of polarization self-screening for improving the electron injection efficiency. In this work, the proposed polarization self-screening effect was studied and proven through growing a p-type EBL with AlN composition partially graded along the [0001] orientation, which induces the bulk polarization charges. These bulk polarization charges are utilized to effectively self-screen the positive polarization induced interface charges located at the interface between the EBL and the last quantum barrier when designed properly. Using this approach, the electron leakage is suppressed and the LED performance is enhanced significantly.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Enhancement of hole injection and electroluminescence by ordered Ag nanodot array on indium tin oxide anode in organic light emitting diode

We report the enhancement of hole injection and electroluminescence (EL) in an organic light emitting diode (OLED) with an ordered Ag nanodot array on indium-tin-oxide (ITO) anode. Until now, most researches have focused on the improved performance of OLEDs by plasmonic effects of metal nanoparticles due to the difficulty in fabricating metal nanodot arrays. A well-ordered Ag nanodot array is fabricated on the ITO anode of OLED using the nanoporous alumina as an evaporation mask. The OLED device with Ag nanodot arrays on the ITO anode shows higher current density and EL enhancement than the one without any nano-structure. These results suggest that the Ag nanodot array with the plasmonic effect has potential as one of attractive approaches to enhance the hole injection and EL in the application of the OLEDs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Breakdown assisted by a novel electron drift injection in the J-TEXT tokamak

A novel electron drift injection (EDI) system aiming to improve breakdown behavior has been designed and constructed on the Joint Texas EXperiment Tokamak Tokamak. Electrons emitted by the system undergo the E×B drift, ∇B drift and curvature drift in sequence in order to traverse the confining magnetic field. A local electrostatic well, generated by a concave-shaped plate biased more negative than the cathode, is introduced to interrupt the emitted electrons moving along the magnetic field line (in the parallel direction) in an attempt to bring an enhancement of the injection efficiency and depth. A series of experiments have demonstrated the feasibility of this method, and a penetration distance deeper than 9.5 cm is achieved. Notable breakdown improvements, including the reduction of breakdown delay and average loop voltage, are observed for discharges assisted by EDI. The lower limit of successfully ionized pressure is expanded.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗