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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.

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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Hall2De Simulations with a First-Principles Electron Transport Model Based on the Electron Cyclotron Drift Instability

Several years of work have combined plasma measurements in a laboratory Hall thruster and r-z numerical simulations with Hall2De to isolate the spatial variation of the anomalous collision frequency needed in Ohm’s law to produce the observed thruster behavior. This numerical solution is used here to test the validity of a first-principles model of the anomalous transport in these devices before such model is implemented self-consistently in r-z fluid codes like Hall2De. The first-principles model employs quasi-linear theory and is based on the hypothesis that the Electron Cyclotron Drift Instability (ECDI) excites ion acoustic turbulence that, in turn, enhances the effective collision frequency in these devices. We find that a model of the ECDI that assumes Maxwellian velocity distributions for electrons and singly-charged, main-beam, cold ions (Ti=0.07 eV) is insufficient to explain the expected variation of the anomalous collision frequency both in the interior and exterior of the acceleration channel. When warm ions (~0.5-3 eV) are accounted for, the ECDI model in the channel interior appears more promising but fails by orders of magnitude in the near plume region due to the much higher Landau damping of the ion acoustic waves there. This implies that either (a) some process allows the ECDI instability to remain uninhibited by classical Landau damping or, (b) that a different instability (or instabilities) altogether, also insusceptible to Landau damping, is/are active in this region. A previous hypothesis, that convection of wave energy generated by the ECDI in the channel plays a significant role in the near plume, is not supported by the results of the simulations.

Mikellides, Ioannis G.↗
NASA NTRS2017

A First-Principles Model Based on Saturation of the Electron Cyclotron Drift Instability for Electron Transport in Hydrodynamics Simulations of Hall Thruster Plasmas

We present a computational model based on the hypothesis that the higher-than-expected electron mobility across magnetic field lines observed in Hall thrusters is due to the growth and eventual saturation of the electron cyclotron drift instability. The key improvement of this model with respect to previous work is that it decouples the saturation of the instability from the correlation that exists between mobility and magnitude of the wave perturbations in linear theory, thereby enabling first-principles simulations. The model has been incorporated in the 2-D (r-z) multi-fluids code Hall2De and simulations of the H6 thruster at 300 V, 20 A are numerically stable and achieve a steady-state solution at a computational cost that is not significantly higher than previous Hall2De simulations. The computed location of the acceleration region is found to be within 10% of the length of the acceleration channel compared to that inferred by experiments. The simulations also capture well the plasma gradients along the channel centerline of this thruster. To further establish the validity of this model, we plan to conduct simulations of other thrusters and/or operating conditions.

Lopez Ortega, Alejandro↗
NASA NTRS2019

Recent Drift and Evolution of Large Icebergs in the Southern Ocean

Tabular icebergs are almost unique to the Southern Ocean because they originate from large ice shelves or ice tongues that are now nearly absent in the Northern Hemisphere. Their evolution from calving to drift to eventual disintegration illustrates many interesting aspects of both glaciology and oceanography. Several events in 2018 highlighted these iceberg processes.

Scardilli, A.↗
NASA NTRS2020

Lower-Hybrid Drift Waves Driving Electron Nongyrotropic Heating and Vortical Flows in a Magnetic Reconnection Layer

We report measurements of lower-hybrid drift waves driving electron heating and vortical flows in an electron-scale reconnection layer under a guide field. Electrons accelerated by the electrostatic potential of the waves exhibit perpendicular and nongyrotropic heating. The vortical flows generate magnetic field perturbations comparable to the guide field magnitude. The measurements reveal a new regime of electron-wave interaction and how this interaction modifies the electron dynamics in the reconnection layer.

L.-J. Chen↗
NASA NTRS2021

The Dispersion of the Modified Two-Stream and Lower Hybrid Drift Instabilities in the Near-pole Plume of a Magnetically Shielded Hall Thruster

Recent analytical and numerical investigations have shown that instabilities in the lower hybrid frequency range can grow in the plume region downstream of the front magnet pole pieces of a magnetically shielded Hall thruster. Growth of the Modified Two-Stream (MTSI) and Lower Hybrid Drift (LHDI) instabilities was found with wave propagation in the r-z (or in-) plane and azimuthal (or out-of-plane) directions, respectively. In the analysis of the LHDI electron collisions were found to be insufficient to quench the instability in a region contained by the thruster ion beam and hollow cathode plume. The implication of the findings is that ions may be heated anomalously by these instabilities, in both the out-of-plane and in-plane directions, thereby altering the velocity field and enhancing the energy of those ions that strike nearby thruster surfaces. In this article we summarize the solution of the dispersion relation for each of these instabilities and provide additional results that can be compared directly with data from future plasma diagnostics, including with direct measurements of the wave dispersion.

Ortega, A. Lopez↗
NASA NTRS2023

3D Simulation of Lower-Hybrid Drift Waves in Strong Guide Field Asymmetric Reconnection in Laboratory Experiments

The magnetic reconnection experiment has recently seen short wavelength (kp (e)(1) lower-hybrid waves near the electron diffusion region in strong guide field reconnection. Based on plasma parameters from the experiment, we perform a three-dimensional fully kinetic simulation in order to investigate the generation of the lower-hybrid waves and their effects on the reconnection process. We find that the low-beta regions around the reconnection site are unstable to the lower-hybrid drift instability propagating in the outflow direction, driven by the difference between the electron and ion outflows. The waves modify the electron distributions, leading to periodic opening and closing of gaps in electron velocity space, and provide a small contribution to the anomalous resistivity. Finally, the simulation results are discussed in the context of space observations and laboratory experiments.

J. Ng↗
NASA NTRSDate not supplied

Are You In or Out: the Influence of Sea Ice Drift on Sea Ice Survivability

The state of Arctic sea ice influences aspects of many global systems including ecosystems, economies, geopolitics, and climate. And, it is in severe decline. Numerous studies have considered the factors that influence Arctic sea ice decline using monthly mean or gridded data. However, these methods struggle to cleanly separate the influences on sea ice melt because the sea ice cover is always moving; thus, different sea ice floes and sea ice regimes constitute the monthly average sea ice state within the Eulerian frame. This study uses a LaGrangian sea ice parcel tracking satellite database to investigate the factors that influence sea ice parcel survivability. The concept of sea ice survivability is defined as the likelihood that a sea ice parcel will last through the summer melt season. Survivability can be stratified in many ways to analyze how it changes as a function of sea ice regime, region, and sea ice characteristics. How is the survivability of first year (FY) and multi-year (MY) ice classes influenced by sea ice motion? This is the central question addressed in this presentation. Specifically, this analysis determines sea ice survivability as a function of distance traveled by sea ice parcels and compares the survivability statistics for sea ice parcels that stay in their starting region versus those that leave their starting region. The preliminary results indicate that the influence of sea ice movement on survivability depends strongly on which region the sea ice resides in at the beginning of the growth season. Lastly, we find substantial inter-annual variability in the regional distribution of sea ice survivability that seems to be strongly linked to sea ice parcel drift between regions of the Arctic Ocean. Moreover, we use these results to discuss the potential contribution of changes in sea ice motion on the observed slowdown in Arctic sea ice extent loss.

Patrick C Taylor↗
DOE OSTI2012

Evolutionary Drift Models for Moving Target Defense

One of the biggest challenges faced by cyber defenders is that attacks evolve more rapidly than our ability to recognize them. We propose a moving target defense concept in which the means of detection is set in motion. This is done by moving away from static signature-based detection and instead adopting biological modeling techniques that describe families of related sequences. We present here one example for how to apply evolutionary models to cyber sequences, and demonstrate the feasibility of this technique on analysis of a complex, evolving software project. Specifically, we applied sequence-based and profile-based evolutionary models and report the ability of these models to recognize highly volatile code regions. We found that different drift models reliably identify different types of evolutionarily related code regions. The impact is that these (and possibly other) evolutionary models could be used in a moving target defense in which the "signature" being used to detect sequence-based behaviors is not a fixed signature but one that can recognize new variants of a known family based on multiple evolutionary models.

Oehmen, Christopher S.↗
DOE OSTI2018

RF AND THERMO-MECHANICAL CONSIDERATIONS IN DESIGNING THE WAVEGUIDE IRIS COUPLER FOR THE DRIFT TUBE LINAC IN THE ORNL SPALLATION NEUTRON SOURCE

The Spallation Neutron Source (SNS) employs tapered ridge waveguide iris couplers to power six drift tube linac (DTL) cavity structures with pulsed RF systems using 2.5MW klystrons at 402.5MHz. All DTL iris couplers have been operating continuously for more than a decade without replacement. Transferring high RF energy to the cavities requires robust RF and mechanical performances with the power dissipation, electrical breakdown and vacuum pressure. Considering the upcoming full 1.4MW operation and the future proton power upgrade (PPU) project, the structural design and the material selection needed to be reviewed for potential spare manufacturing. The existing design and the modified design with improvements of the coupler have been numerically studied. For the study, 3D models were used for RF and structural characterizations of the waveguide iris couplers on the DTL cavity. RF and thermo-mechanical co-simulations were performed to assess the effects of using the different materials and the structural modification.

Lee, Sung-Woo↗
DOE OSTI2020

Suppressing Coherent Gauge Drift in Quantum Simulations

Simulations of field theories on noisy quantum computers must contend with errors introduced by that noise. For gauge theories, a large class of errors violate gauge symmetry, and thus may result in unphysical processes occurring in the simulation. We present a method, applicable to non-Abelian gauge theories, for suppressing coherent gauge drift errors through the repeated application of pseudorandom gauge transformation. In cases where the dominant errors are gauge-violating, we expect this method to be a practical way to improve the accuracy of NISQ-era simulations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Tunnel drift step recovery diode

Devices, methods and techniques are disclosed for providing a multi-layer diode without voids between layers. In one example aspect, a multi-stack diode includes at least two Drift Step Recovery Diodes (DSRDs). Each DSRD comprises a first layer having a first type of dopant, a second layer forming a region with at least ten times lower concentration of dopants compared to the adjacent layers, and a third layer having a second type of dopant that is opposite to the first type of dopant. The first layer of a second DSRD is positioned on top of the third layer of first DSRD. The first layer of the second DSRD and the third layer of the first DSRD are degenerate to form a tunneling diode at an interface of the first DSRD and second DSRD, the tunneling diode demonstrating a linear current-voltage characteristic.

Voss, Lars F.↗
DOE OSTI2023

Design and fabrication of the waveguide Iris couplers for the Spallation Neutron Source drift tube linac

The Spallation Neutron Source (SNS) employs six cavities in the Drift Tube Linac (DTL) section to accelerate the H- ion beam to 87MeV. Each cavity is energized by a 2.5MW peak power klystron at 402.5MHz using rapid tapered waveguide iris couplers. All six original iris couplers have been in operation without replacement for over two decades. The increased RF power demands of the Proton Power Upgrade (PPU) project and operational problems, including arcing, temperature excursions, and vacuum bursts, have prompted the development of new iris coupler spares. The original iris couplers were made of GlidCop material, which is known to be mechanically strong and thermally stable, but is porous, expensive, and difficult to use in fabrication. To overcome these problems, the new spare couplers use Oxygen-Free Copper (OFC) and stainless steel (SS). This paper will discuss the mechanical, thermal and RF design, as well as challenges in the final coupler fabrication.

Lee, Sung-Woo↗
DOE OSTI2022

Gaussian process for calibration and control of GlueX Central Drift Chamber

We have developed and implemented a machine learning based system to calibrate and control the GlueX Central Drift Chamber at Jefferson Lab, VA, in near real-time. The system monitors environmental and experimental conditions during data taking and uses those as inputs to a Gaussian process (GP) with learned prior. The GP predicts calibration constants in order to recommend a high voltage (HV) setting for the detector that maintains consistent detector performance (gain and resolution) throughout data taking. This approach is in stark contrast to traditional detector operations in which the detector operates at fixed HV and its calibration parameters vary quite considerably with time. Additionally, the ML based system utilizes uncertainty quantification to correct the recommended control parameters when appropriate. We will present results from the ML system autonomously during the Charged Pion Polarizability (CPP) experiment conducted in Hall D at Jefferson Lab.

McSpadden, Helen↗
DOE OSTI2026

Wasserstein Normalized Autoencoder for Anomaly Detection in ProtoDUNE Vertical-Drift Detector

ProtoDUNE Vertical Drift needs a selective triggering algorithm. The detector sits on Earth's surface, so cosmic activity dominates its data. Our goal in this paper is to trigger on neutrino events more robustly than the current deployed Analog-to-Digital Converter Simple Window (ADCSW) model and, eventually, search for signals of Beyond Standard Model (BSM) physics at DUNE as our ultimate North Star objective. As a step towards this goal, we evaluate a Wasserstein Normalized Autoencoder (WNAE) on simulated collection-plane only windows of shape $1\times10\times10$ where Neutrinos act as our BSM-proxy and Cosmic-ray Muons serve as our learned background. The network parameters are fitted using only cosmic-ray muon events as background in order to maintain an unsupervised pipeline. Training uses finite-step Langevin $x^-$ samples, positive-sample reconstruction energy, and an empirical sliced $2$-Wasserstein objective to learn a normalized Boltzmann energy model. We then calibrate on a nominal $5\,\mathrm{Hz}$ operating threshold calculated from cosmic validation data. Both WNAE and ADCSW accept 311 of 194,083 held-out cosmic background events at this $5\,\mathrm{Hz}$ threshold. We found that WNAE accepts 9,677 of 34,634 neutrino-proxy events $(27.9\pm0.24)\%$, compared with 10,076 $(29.1\pm0.24)\%$ for ADCSW, an observed WNAE-minus-ADCSW difference of $-1.15\%$. At another nominal $2\,\mathrm{Hz}$ target threshold, the corresponding efficiencies are $(20.5\pm0.22)\%$ and $(22.6\pm0.22)\%$, respectively. Of the WNAE-selected neutrino proxies at $5\,\mathrm{Hz}$, $(20.8\pm0.4)\%$ of the classified neutrino-proxy events are unique to WNAE, where the uncertainty is an absolute binomial standard error of $0.4\%$.

Zheng, Jake [Chicago U.] (ORCID:0009000218901379)↗
DOE OSTI2026

Real-Time Anomaly Detection for Searches Beyond the Standard Model in the ProtoDUNE Horizontal Drift Detector

This paper summarizes work conducted throughout a SULI internship at Fermi National Accelerator Laboratory focused on building an unsupervised machine learning model for real-time anomaly detection in ProtoDUNE Horizontal Drift. Using simulated data, we trained an autoencoder model on a pure cosmic dataset, and evaluated it on both cosmic and neutrino events—making the model an anomaly detector. The goal was to make a model which matches or exceeds the current ADC Simple Window trigger algorithm so that our model can perform at the same rate but provide sensitivity to potential beyond-the-Standard-Model (BSM) signatures. In the end, we were able to construct a model which slightly exceeds the capabilities of the ADC Simple Window while remaining completely unsupervised, achieving 31.9 ± 0.2% (26.6 ± 0.2%) ν efficiency at 5 Hz (2 Hz), a 3.6 (3.2) percentage point increase. Additionally, 17.5 ± 0.3% (18.3 ± 0.3%) of the events that passed the autoencoder at 5 Hz (2 Hz) were missed by the current trigger algorithm. Future work will investigate alternative normalization methods, including quantile transformation, and evaluate the model on ProtoDUNE-HD detector-glitch data if that data becomes available.

Wilson, C. [Cincinnati U., RWC]↗
DOE OSTI2018

Coupling of a High-Resolution Ambient Pressure Drift Tube Ion Mobility Spectrometer to a Commercial Time-of-flight Mass Spectrometer

Ion mobility spectrometry provides information about molecular structures of ions. Hence, high resolving power allows separation of isomers which is of major interest in several applications. In this work, we couple our high-resolution ion mobility spectrometer (IMS) with a resolving power of R{sub p} = 100 to a time-of-flight mass spectrometer (TOF-MS). Besides, the benefit of an increased resolving power such an IMS-MS also helps analyzing and understanding the ionization processes in IMS. Usually, the coupling between IMS and TOF-MS is realized by synchronizing data acquisition of the IMS and MS resulting in two-dimensional data containing ion mobility and mass spectra. However, due to peak widths of less than 100 μs in our high-resolution IMS, this technique is not practicable due to significant peak broadening during the ion transfer into the MS and an insufficient data acquisition rate of the MS. Thus, a novel but simple interface between the IMS and MS has been designed which minimizes ion losses, allows recording of ion mobility at full IMS resolving power, and enables a shuttered transmission of ions into the MS. The interface is realized by replacing the Faraday plate used in IMS by a Faraday grid that is shielded by two additional aperture grids. For demonstration, positive product ions of benzene, toluene, and m-xylene in air are investigated. The IMS is equipped with a radioactive {sup 3}H source. Besides the well-known product ions M{sup +} and M·NO{sup +}, a dimer ion is also observed for benzene and toluene, consisting of two molecules and three further hydrogen atoms. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Substance P in the Gas Phase: Conformational Changes and Dissociations Induced by Collisional Activation in a Drift Tube

The work presented below is related to our companion paper in this issue, entitled: Substance P in solution: trans-to-cis configurational changes of penultimate prolines initiate non-enzymatic peptide bond cleavages. Two-dimensional ion mobility spectrometry (IMS-IMS) and mass spectrometry techniques are used to investigate structural transitions for [M+3H]{sup 3+} ions of substance P (subP) upon collisional activation (CA) in the gas phase. In this approach, different conformations of ions having a specified mobility are selected after an initial IMS separation, collisionally activated to produce new conformers, and these product structures are separated again using a second IMS region. In this way, it is possible to follow folding and unfolding transitions of different conformations. The analysis shows evidence for five conformations. Unlike other systems, every transition is irreversible. Studies as a function of activation voltage are used to discern pathways of structural changes prior to reaching the energy required for dissociation. Thresholds associated with the onsets of transitions are calibrated to obtain estimates of the energetic barriers between different structures and semi-quantitative potential energy diagrams are presented. Overall, barriers associated with structural transitions of [subP+3H]{sup 3+} in the absence of solvent are on the order of ~ 40 kJ mol{sup −1}, substantially lower than the ~ 90 kJ mol{sup −1} required for some similar structural transitions in solutions of ethanol. Comparisons of the transition energies in the gas phase with thermochemistry for similar transitions in solution provide clues about why reverse transitions are prohibited. .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗