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At least 1,135 records · Page 63

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NASA NTRS1980

Exploring the veiled planet

An overview of data obtained from various experiments which characterize geological features and atmospheric properties of Venus is presented. Data from the two Pioneer sounder probes (one located at Venus's equator and the other near the north pole) exhibit a reversal in the equator-to-pole temperature patterns at 60 km altitude which suggests that two circulation cells exist within the atmospheric region. However, the atmospheric temperature and pressure beneath the clouds are found to be nearly identical everywhere on Venus and both temperature and pressure conditions at the surface are lower than first expected. The identification of sulphur dioxide clouds which appear to coincide with Venus's characteristic global patterns of C- and Y-shaped dark markings support the hypothesis of a regular pattern of planet spanning breaks in the upper cloud layer. Explanations of a Venus sulphur cycle and of observed magnetic field structures are suggested

Source record↗

NASA NTRS1988

Cross-B convection of artificially created, negative-ion clouds and plasma depressions - Low-speed flow

A negative-ion, positive-ion plasma produced by the release of an electron attachment chemical into the F region becomes electrically polarized by collisions with neutrals moving across magnetic field lines. The resulting electric field causes E x B drift of the two ion species and the residual electrons. The cross-field flow of the modified ionosphere is computed using a two-dimensional numerical simulation which includes electron attachment and mutual neutralization chemistry, self-consistent electric fields, and three-species plasma transport. The velocity of the plasma is initially in the direction of the neutral wind because the negative-ion cloud is a Pedersen conductivity enhancement. As the positive and negative ions react, the Pedersen conductivity becomes depressed below the ambient value and the velocity of the plasma reverses direction. A plasma hole remains after the positive and negative ions have mutually neutralized. The E x B gradient drift instability produces irregularities on the upwind edge of the hole.

Bernhardt, Paul A.↗

DOE OSTI2022

Performance Leap of Lithium Metal Batteries in LiPF 6 Carbonate Electrolyte by a Phosphorus Pentoxide Acid Scavenger

Phosphorus pentoxide (P 2 O 5 ) is investigated as an acid scavenger to remove the acidic impurities in a commercial lithium hexafluorophosphate (LiPF 6 ) carbonate electrolyte to improve the electrochemical properties of Li metal batteries. Nuclear magnetic resonance (NMR) measurements reveal the detailed reaction mechanisms of P 2 O 5 with the LiPF 6 electrolyte and its impurities, which removes hydrogen fluoride (HF) and difluor-ophosphoric acid (HPO 2 F 2 ) and produces phosphorus oxyfluoride (POF 3 ), OF 2 P-O-PF 5 - anions, and ethyl difluorophosphate (C 2 H 5 OPOF 2 ) as new electrolyte species. The P 2 O 5 -modified LiPF 6 electrolyte is chemically compatible with a Li metal anode and LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) cathode, generating a PO x F y -rich solid electrolyte interphase (SEI) that leads to highly reversible Li electrodeposition, while eliminating transition metal dissolution and cathode particle cracking. The excellent electrochemical properties of the P 2 O 5 -modified LiPF6 electrolytes are demonstrated on Li||NMC622 pouch cells with 0.4 Ah capacity, 50 mu m Li anode, 3 mAh cm -2 NMC622 cathode, and 3 g Ah -1 electrolyte/capacity ratio. The pouch cells can be galvanostatically cycled at C/3 for 230 cycles with 87.7% retention.

25 ENERGY STORAGE↗

DOE OSTI2025

On resistive interchange, double tearing, and resonant and non-resonant infernal modes in spherical tokamak negative central shear discharges

We examine the linear and nonlinear stability of a sequence of reversed shear NSTX equilibria with the same toroidal current density and pressure profile but with different toroidal field strengths. All equilibria have two q = 2 surfaces and have q > 1 everywhere. For this sequence, which all have β P ∼ 0.5, as the minimum value of q decreases below about 1.4, the localized resistive interchange criterion is strongly violated, and the unstable mode with toroidal mode number n=1 changes its dominant poloidal mode number m from a (m,n)=(2,1) double tearing mode to a non-resonant (1,1) infernal mode. This (1,1) mode nonlinearly flattens both the current density and the pressure near the magnetic axis. The higher-n unstable modes are all resistive infernal modes localized around the surface where q has a minimum and the magnetic shear vanishes. They generally saturate nonlinearly at low amplitude but can cause magnetic surface breakup near the axis.

Spitzer resistivity↗

DOE OSTI2022

Fast Particle-Wave Interactions and Alfvén Eigenmodes in JET Tokamak Plasmas

This document serves as the closeout report of DOE Grant Award No. DE-FG02-99ER54563 with project period 1 April 2015 through 31 March 2020. The project comprised the international collaboration between MIT and EU scientists on the JET facility to improve our understanding of the physics of energetic particle-wave interactions by measuring the damping rates of stable Alfvén Eigenmodes (AEs) and unstable energetic particle driven modes. More specifically, this project involved the continued participation of MIT, the Culham Centre for Fusion Energy, the Swiss Plasma Center, and theorists from various European laboratories and from UC Irvine. Past contributions from the University of São Paulo are gratefully acknowledged. The Alfvén Eigenmode Active Diagnostic (AEAD) on JET discharges was successfully upgraded in this period and has extracted physically useful information, in primarily deuterium plasma discharges. It is expected that such experiments would be continued during the DT campaign in CY 2021 to assess the damping rates of similar modes in the presence of alpha particles, a product of fusing burning plasma. Only JET would carry out such experiments in the near term in the world. It is important to note that this collaboration was continued under DOE Grant Award No. DE-SC0014264 from 1 April 2020 through the present. In this grant period, the AEAD was upgraded with a set of individual amplifiers for each of a set of six antennas in two toroidally opposite locations. These new amplifiers allowed targeted selection of the antennas’ toroidal spectrum for AEs of interest with toroidal mode number | n | ≤ 20. The resonant detection and measurement of the damping rates of AEs was obtained from magnetic probes that could be compared with theory and simulations. This is a key topic of investigation for ITER and all other next-step fusion experiments, where such modes will interact with energetic particles produced by fusion reactions (alpha particles), Neutral Beam Injection (NBI) and Ion Cyclotron Resonance Heating (ICRH). The majority of the observations during this period were of Toroidal Alfvén Eigenmodes (TAEs) as these are most commonly observed on JET; a number of measurements were made during dedicated TAE experiments. However, a new set of lower frequency band filters were procured with the goal of studying Geodesic Acoustic Modes (GAMs), Beta (Acoustic) AEs (BAE/BAAEs), and Reverse Shear AEs (RSAEs), also predicted by theory. Commissioning and optimizations were successfully completed in this period, and the diagnostic has been in operation during the more recent JET campaigns. Initial results have been obtained in dedicated TAE experiments and successfully compared to drift-kinetic theory. A wide range of theoretical studies have been undertaken in support of the upcoming JET campaigns experiments. To supplement the ongoing use of ideal MHD codes, such as MISHKA during the studies of TAEs, gyrokinetic simulations of low frequency AEs were performed in collaboration with UC Irvine. The Gyrokinetic Toroidal Code (GTC) was used to determine the structure, frequencies and stability of AEs in JET plasmas. Thus, a solid scientific foundation has been laid for future DT campaigns in JET in the 2021 operation period when the damping rates of relevant modes in the presence of alpha particles could be assessed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1973

Whistler waves observed upstream from collisionless shocks

Waves in the frequency range 0.5 - 4 Hz were studied in the region upstream of the earth's bow shock using data from the fluxgate magnetic field experiment on IMP-6. Analysis of 150 examples of these waves during a three month interval indicates that amplitudes are generally less than 1 or 2 gammas and propagation directions generally make angles of between 20 and 40 degrees with the field direction. The waves as measured in the spacecraft frame of reference are either left or right hand polarized with respect to the average field direction. It is concluded that the observed waves are right handed waves in the plasma frame of reference with wavelengths of approximately 100 km propagating upstream in the whistler mode. Doppler shifting reduces the observed frequencies in the spacecraft frame and reverses the observed polarization for those waves propagating more directly upstream. Similar waves are seen ahead of most interplanetary shocks.

Fairfield, D. H.↗

NASA NTRS1989

Large-scale fluctuations in the solar wind at 1 AU - 1978-1982

The large-scale fluctuations in the strength of the magnetic field B and the bulk speed V at 1 AU were investigated on the basis of hourly averages of IMP 8 and ISEE 3 data compiled by Couzens and King (1986). The power spectra of the intermediate frequency fluctuations in B at 1 AU had the form of a power law with exponent 1.92 + or - 0.06 during the 1978-1982 interval. The contributions of jumps to the spectra of the large-scale fluctuations in B and V were studied for the interval from days 226 to 365, 1978, which is representative of other such intervals. Of the jumps in B, 22 percent have the signature of a forward or reverse shock.

Burlaga, L. F.↗

NASA NTRS2013

Measurements of Cyclotron Features and Pulse Periods in the High-Mass X-Ray Binaries 4U 1538-522 and 4U 1907+09 with the International Gamma-Ray Astrophysics Laboratory

We present a spectral and timing analysis of International Gamma-Ray Astrophysics Laboratory (INTEGRAL) observations of two high-mass X-ray binaries, 4U 1538−522 and 4U 1907+09. Our timing measurements for 4U 1538−522 find the pulse period to have exhibited a spin-up trend until approximately 2009, after which there is evidence for a torque reversal, with the source beginning to spin down to the most recently measured period of 525.407 plus or minus 0.001 seconds. The most recent INTEGRAL observations of 4U 1907+09 are not found to yield statistically significant pulse periods due to the significantly lower flux from the source compared with 4U 1538−522. A spectral model consisting of a power-law continuum with an exponential cutoff and modified by two cyclotron resonance scattering features is found to fit both sources well, with the cyclotron scattering features detected at approximately 22 and approximately 49 kiloelectronvolts for 4U 1538−522 and at approximately 18 and approximately 36 kiloelectronvolts for 4U 1907+09. The spectral parameters of 4U 1538−522 are generally not found to vary significantly with flux and there is little to no variation across the torque reversal. Examining our results in conjunction with previous work, we find no evidence for a correlation between cyclotron line energy and luminosity for 4U 1538−522. 4U 1907+09 shows evidence for a positive correlation between cyclotron line energy and luminosity, which would make it the fourth, and lowest luminosity, cyclotron line source to exhibit this relationship.

stars: magnetic field↗

NASA NTRS2018

Long-Term Solar Activity Studies Using Microwave Imaging Observations and Prediction for Cycle 25

We use microwave imaging observations from the Nobeyama Radioheliograph at 17 GHz for long-term studies of solar activity. In particular, we use the polar and low-latitude brightness temperatures as proxies to the polar magnetic field and the active-regions, respectively. We also use the location of prominence eruptions as a proxy to the filament locations as a function of time. We show that the polar microwave brightness temperature is highly correlated with the polar magnetic field strength and the fast solar wind speed. We also show that the polar microwave brightness at one cycle is correlated with the low latitude brightness with a lag of about half a solar cycle. We use this correlation to predict the strength of the solar cycle: the smoothed sunspot numbers in the southern and northern hemispheres can be predicted as 89 and 59, respectively. These values indicate that cycle 25 will not be too different from cycle 24 in its strength. We also combined the rush to the pole data from Nobeyama prominences with historical data going back to 1860 to study the north-south asymmetry of sign reversal at solar poles. We find that the reversal asymmetry has a quasi-periodicity of 3-5 cycles.

N. Gopalswamy↗

DOE OSTI2021

Anomalous normal fluid response in a chiral superconductor UTe2

Abstract Chiral superconductors have been proposed as one pathway to realize Majorana normal fluid at its boundary. However, the long-sought 2D and 3D chiral superconductors with edge and surface Majorana normal fluid are yet to be conclusively found. Here, we report evidence for a chiral spin-triplet pairing state of UTe 2 with surface normal fluid response. The microwave surface impedance of the UTe 2 crystal was measured and converted to complex conductivity, which is sensitive to both normal and superfluid responses. The anomalous residual normal fluid conductivity supports the presence of a significant normal fluid response. The superfluid conductivity follows the temperature behavior predicted for an axial spin-triplet state, which is further narrowed down to a chiral spin-triplet state with evidence of broken time-reversal symmetry. Further analysis excludes trivial origins for the observed normal fluid response. Our findings suggest that UTe 2 can be a new platform to study exotic topological excitations in higher dimension.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Gyrokinetic simulations of momentum flux parasitic to free-energy transfer

Ion Landau damping interacts with a portion of the E×B drift to cause a non-diffusive outward flux of co-current toroidal angular momentum. Quantitative evaluation of this momentum flux requires nonlinear simulations to determine fL, the fraction of fluctuation free energy that passes through ion Landau damping, in fully developed turbulence. Nonlinear gyrokinetic simulations with the GKW code confirm the presence of the systematic symmetry-breaking momentum flux. For simulations with adiabatic electrons, fL scales inversely with the ion temperature gradient, because only the ion curvature drift can transfer free energy to the electrostatic potential. Although kinetic electrons should in principle relax this restriction, the ion Landau damping measured in collisionless kinetic-electron simulations remained at low levels comparable with ion-curvature-drift transfer, except when magnetic shear was strong. A set of simulations scanning the electron pitch-angle scattering rate showed only a weak variation of fL with the electron collisionality. However, collisional-electron simulations with electron temperature greater than ion temperature unambiguously showed electron-curvature-drift transfer supporting ion Landau damping, leading to a corresponding enhancement of the symmetry-breaking momentum flux.

intrinsic rotation↗

DOE OSTI2026

Impact of reverse flow induced by a sawtooth anode on the performance of an argon Hall thruster

This study reports the performance comparison of the RAIJIN-66 TAL-type Hall thruster with argon propellant, using two hollow anode designs, one with a simple straight shape and another one with a sawtooth shape. Simulations of the rarefied gas in the sawtooth hollow anode region suggest a successful reversal of the direction of neutral particle flow, with an average increase in the neutral particle density by 15.5% when compared to the straight-shaped hollow anode. This contributes to the improvement in performance across a range of discharge voltages that was measured experimentally. When the thruster is operated with a discharge voltage of 150 V and a flow rate of 70 SCCM, the propellant utilization efficiency with the straight anode is 14%, while with the sawtooth anode it is 25.1%. The anode efficiency reaches in the vicinity of 15% with the sawtooth anode in high voltage conditions, exceeding the efficiencies achieved with the straight anode in the same operating conditions. The optimal magnetic field condition for argon operation and the tuning parameters of the sawtooth anode design for RAIJIN-66 are also discussed.

Satpathy, Dibyesh [Univ. of Tokyo (Japan)] (ORCID:↗

NASA NTRS2008

Laboratory-Model Integrated-System FARAD Thruster

Pulsed inductive plasma accelerators are spacecraft propulsion devices in which energy is stored in a capacitor and then discharged through an inductive coil. The device is electrodeless, inducing a plasma current sheet in propellant located near the face of the coil. The propellant is accelerated and expelled at a high exhaust velocity (order of 10 km/s) through the interaction of the plasma current with an induced magnetic field. The Faraday Accelerator with RF-Assisted Discharge (FARAD) thruster [1,2] is a type of pulsed inductive plasma accelerator in which the plasma is preionized by a mechanism separate from that used to form the current sheet and accelerate the gas. Employing a separate preionization mechanism in this manner allows for the formation of an inductive current sheet at much lower discharge energies and voltages than those found in previous pulsed inductive accelerators like the Pulsed Inductive Thruster (PIT). In a previous paper [3], the authors presented a basic design for a 100 J/pulse FARAD laboratory-version thruster. The design was based upon guidelines and performance scaling parameters presented in Refs. [4, 5]. In this paper, we expand upon the design presented in Ref. [3] by presenting a fully-assembled and operational FARAD laboratory-model thruster and addressing system and subsystem-integration issues (concerning mass injection, preionization, and acceleration) that arose during assembly. Experimental data quantifying the operation of this thruster, including detailed internal plasma measurements, are presented by the authors in a companion paper [6]. The thruster operates by first injecting neutral gas over the face of a flat, inductive acceleration coil and at some later time preionizing the gas. Once the gas is preionized current is passed through the acceleration coil, inducing a plasma current sheet in the propellant that is accelerated away from the coil through electromagnetic interaction with the time-varying magnetic field. Neutral gas is injected over the face of the acceleration coil through a fast-acting valve that feeds a central distribution manifold. The thruster is designed to preionize the gas using an RF-frequency ringing signal produced by a discharging Vector Inversion Generator (VIG). The acceleration stage consists of a multiple-turn, multiple-strand spiral induction coil (see Fig. 1, left panel) and is designed for operation at discharge energies on the order of 100 J/pulse. Several different pulsed power train modules can be used to drive current through the acceleration coil. One such power train is based upon the Bernardes and Merryman circuit topology, which restricts voltage reversal on the capacitor banks and can be clamped to eliminate current reversal in the coil. A second option is a pulse-compression-ring power train (see Fig. 1, right panel), which takesa temporally broad, low current pulse and transforms it into a short, high current pulse.

Polzin, K.A.↗

DOE OSTI2023

Ultrahigh‐Flux X‐ray Detection by a Solution‐Grown Perovskite CsPbBr 3 Single‐Crystal Semiconductor Detector

Abstract Solution‐processed perovskites are promising for hard X‐ray and gamma‐ray detection, but there are limited reports on their performance under extremely intense X‐rays. Here, a solution‐grown all‐inorganic perovskite CsPbBr 3 single‐crystal semiconductor detector capable of operating at ultrahigh X‐ray flux of 10 10 photons s −1 mm −2 is reported. High‐quality solution‐grown CsPbBr 3 single crystals are fabricated into detectors with a Schottky diode structure of eutectic gallium indium/CsPbBr 3 /Au. A high reverse‐bias voltage of 1000 V (435 V mm − 1 ) can be applied with a small and stable dark current of ≈60–70 nA (≈9–10 nA mm − 2 ), which enables a high sensitivity larger than 10 000 µC Gy air −1 cm − 2 and a simultaneous low detection limit of 22 nGy air s − 1 . The CsPbBr 3 semiconductor detector shows an excellent photocurrent linearity and reproducibility under 58.61 keV synchrotron X‐rays with flux from 10 6 to 10 10 photons s − 1 mm − 2 . Defect characterization by thermally stimulated current spectroscopy shows a similar low defect density of a synchrotron X‐ray and a lab X‐ray irradiated device. Solid‐state nuclear magnetic resonance spectroscopy suggests that the excellent performance of the solution‐grown CsPbBr 3 single crystal may be associated with its good short‐range order, comparable to the spectrometer‐grade melt‐grown CsPbBr 3 .

Pan, Lei↗

NASA NTRS1992

How the effects of winds and electric fields in F2-layer storms vary with latitude and longitude - A theoretical study

The effects of thermospheric winds and electric fields on the ionospheric F2-layer are controlled by the geometry of the magnetic field, and so vary with latitude and longitude. A simple model of the daytime F2-layer is adopted and the effects at midlatitudes (25-65 deg geographic) of three processes that accompany geomagnetic storms: (1) thermospheric changes due to auroral heating; (2) equatorward winds that tend to cancel the quiet-day poleward winds; and (3) the penetration of magnetospheric electric fields are studied. At +/- 65 deg, the effects of heating and electric fields are strongest in the longitudes toward which the geomagnetic dipole is tilted, i.e., the North American and the South Indian Ocean sectors. Because of the proximity of the geomagnetic equator to the East Asian and South American sectors, the reverse is true at +/- 25 deg.

Mendillo, M.↗

NASA NTRS2022

“The Goose” Pulsar Wind Nebula of PSR J1016–5857: The Birth of a Plerion

We report the results of X-ray (CXO) and radio (ATCA) observations of the pulsar wind nebula(PWN) powered by the young pulsar PSR J1016–5857, which we dub “the Goose” PWN. In bothbands the images reveal a tail-like PWN morphology which can be attributed to pulsar’s motion. Bycomparing archival and newCXOobservations, we measure the pulsar’s proper motionμ= 28.8±7.3mas yr−1, yielding a projected pulsar velocityv≈440±110 km s−1(atd= 3.2 kpc); its direction isconsistent with the PWN shape. Radio emission from the PWN is polarized, with the magnetic fieldoriented along the pulsar tail. The radio tail connects to a larger radio structure (not seen in X-rays)which we interpret as a relic PWN (also known as a plerion). The spectral analysis of theCXOdatashows that the PWN spectrum softens from Γ = 1.7 to Γ≈2.3−2.5 with increasing distance fromthe pulsar. The softening can be attributed to the rapid synchrotron burn-off, which would explainthe lack of X-ray emission from the older relic PWN. In addition to non-thermal PWN emission, wedetected thermal emission from a hot plasma which we attribute to the host SNR. The radio PWNmorphology and the proper motion of the pulsar suggest that the reverse shock passed through thepulsar’s vicinity and pushed the PWN to one side.

Pulsars↗

NASA NTRS1982

Remote flare brightenings and type III reverse slope bursts

Observations are presented on two large (H-alpha class 2) flares that each produced an extensive chain of discrete H-alpha brightenings spanning 370,000-470,000 km in length in remote quiet regions more than 100,000 km from the main flare site. A large group of Type III RS bursts was also observed accompanying each flare. The onset of about half the remote H-alpha emission patches were nearly simultaneous with the RS bursts. One flare was observed in hard X-rays, and it is noted that the RS bursts occurred during hard X-ray spikes. For the other flare, soft X-ray filtergrams indicate coronal loops connecting from the main flare site to the remote H-alpha brightenings. Observations indicate that the RS burst electrons were generated in the flares, and it is proposed that the remote H-alpha brightenings were initiated by direct heating of the chromosphere by RS burst electrons traveling in closed magnetic loops connecting the flare site to the remote patches. It is also suggested that after onset, the brightenings were heated by thermal conduction by slower thermal electrons.

Tang, F.↗

DOE OSTI2025

Néel domain walls with bistable chirality in a perpendicularly magnetized ferrimagnetic insulator

Field-free spin-orbit torque-driven domain wall motion in magnetic thin films with perpendicular magnetic anisotropy (PMA) requires the domain walls to have Néel character. Conventionally, Néel domain walls are stabilized by the Dzyaloshinskii-Moriya interaction (DMI) in ultrathin films. Here, in a europium iron garnet thin film with PMA and an additional uniaxial in-plane anisotropy, we demonstrate two bistable Néel domain wall states in the absence of DMI, and the capability to toggle the wall states with an in-plane field pulse and consequently their directions of motion under a current pulse. We present a phase diagram for the bistable Néel domain wall states as a function of in-plane field pulse width and amplitude. By fitting the experimental data to an analytical model of Néel wall reversal through the nucleation and propagation of Bloch lines, we extract the length of the initial reversed domain wall segment and Bloch line nucleation energy barrier. Current-driven motion of in-plane anisotropy stabilized Néel walls is qualitatively different from that of DMI-stabilized ones owing to the different symmetry of the effective fields that stabilize the Néel configuration. Furthermore, we present a proof of principle demonstration for 2-bit random number generation based on the stochastic reversal of domain wall chirality. These results provide critical insight into the topological energy barrier of Bloch lines and identify paths towards domain wall-based memory and computing devices.

36 MATERIALS SCIENCE↗