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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

AMPTE CCE observations of Pc 3-4 pulsations at L = 2-6

Magnetic field data acquired by the AMPTE CCE satellite from L = 2-6 are analyzed. A procedure was specially developed to reduce the artificial modulation and noise in magnetic field measurements, making it possible to detect Pc 3-4 pulsations with amplitudes only 1 nT or less, even for L values less than 3. A survey of 41 CCE passes in L = 2-6 and in the postnoon sector showed that the most commonly observed pulsations in this region were the east-west oscillations of magnetic field with clearly L-dependent frequencies; these are identified as the toroidal mode standing Alfven waves. A relationship was found between the pulsation frequency and plasma density, showing that the pulsation data can be used to estimate the plasma mass density in the inner magnetosphere.

Takahashi, Kazue↗
DOE OSTI2022

High resolution density pedestal measurements during edge localized modes by short-pulse reflectometry in the TCV tokamak

This publication presents high spatio-temporal resolution (mm/μs) density profile measurements of the pedestal top during type I, III, and small edge localized mode (ELM) H-mode plasmas in the Tokamak à Configuration Variable (TCV). These measurements were performed using a novel short-pulse reflectometer. Average inter-ELM density profiles are obtained via conditional averaging using the Dα trace as ELM indicator. Changes to the pedestal density profile gradients prior to type-III ELMs reveal unique pedestal dynamics leading to the ELM crash which can provide important experimental data for validation of non-linear MHD ELM simulations. The small-ELM scenario is found to feature a ∼25-35 kHz quasi-coherent density fluctuation near the separatrix rho_psi ∼0.993-1.05 not observed during a similar type-I ELM discharge. This oscillation is also found in low-field-side magnetic pick- up probes displaying a ballooning character and n=+1 toroidal mode number. This oscillation could help explain the markedly different pedestal dynamics observed in the small-ELM regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

High resolution density pedestal measurements during edge localized modes by short-pulse reflectometry in the TCV tokamak

Here, this publication presents high spatio-temporal resolution (mm µs -1 ) density profile measurements of the pedestal top during type I, III, and small edge localized mode (ELM) H-mode plasmas in the tokamak à configuration variable (TCV). These measurements were performed using a novel short-pulse reflectometer. Average inter-ELM density profiles are obtained via conditional averaging using the D α trace as ELM indicator. Changes to the pedestal density profile gradients prior to type-III ELMs reveal unique pedestal dynamics leading to the ELM crash which can provide important experimental data for validation of non-linear MHD ELM simulations. The small-ELM scenario is found to feature a ~25–35 kHz quasi-coherent density fluctuation near the separatrix ρ ψ 0.993–1.05 not observed during a similar type-I ELM discharge. This oscillation is also found in low-field-side magnetic pick-up probes displaying a ballooning character and n = +1 toroidal mode number. This oscillation could help explain the markedly different pedestal dynamics observed in the small-ELM regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2017

Critical Fluctuations in Beam-Plasma Systems and Solar Type III Radio Bursts

The type III radio bursts are the most intense radio emissions from the sun. In Figure 1, we present a typical type III burst observed by the STEREO spacecraft. Ginzburg and Zheleznyakov (1958) were the first to suggest that Langmuir waves excited by the solar flare accelerated electrons are the source of these bursts. The in situ detection of electron beams and Langmuir waves in association with type III bursts together with tracking of type III burst sources in the interplanetary medium confirmed this plasma hypothesis. However, the dynamics of type III electron beams and their interaction with the ambient plasma through the excited Langmuir waves is an unsolved problem. In order that the electron beams don't lose their energy by resonantly interacting with Langmuir waves, various nonlinear processes, such as the induced scattering of Langmuir waves off the background ions in weak turbulence regime and oscillating two-stream instability in strong turbulence regime were invoked. However, the observed electron density fluctuations do not allow Langmuir waves to grow to very high intensities as pointed out by several authors. As far as the conversion of Langmuir wave energy into electromagnetic energy is concerned, there is no consensus either for the fundamental or for the second harmonic emission. In this paper, we address these issues in terms of critical fluctuations near the boundary of the beam-plasma instability which is analogous to the anomalously growing fluctuations near the phase transition points called critical points. We show that this phenomenon can account for the survival of electron beams over large distances as well as the intensities of Langmuir waves excited during this phase transition regime are sufficient to explain the peak intensities of the fundamental as well as harmonic emissions

Fluctuations↗
NASA NTRS1994

Kinetic and thermodynamic properties of a convecting plasma in a two-dimensional dipole field

Charged particle guiding center motion is considered in the magnetic field of a two-dimensional ('line') dipole on which is superimposed a small, static, perpendicular electric field. The parallel equation of motion is that of a simple harmonic oscillator for cos theta, the cosine of magnetic colatitude theta. Equations for the perpendicular electric and magnetic drifts are derived as well as their bounce-averaged forms. The latter are solved to yield a bounce-averaged guiding center trajectory, which is the same as that obtained from conversation of magnetic moment mu, longitudinal invariant J, and total (kinetic plus electrostatic) energy K. The algebraic simplicity of the trajectory equations is also manifest in the forms of the invariants. An interesting result is that guiding centers drift in such a way that they preserve the values of their equatorial pitch angles and (equivalently) mirror latitudes. The most general Maxwellian form of the equilibrium one-particle distribution function f is constructed from the invariants, and spatially varying density and pressure moments, parallel and perpendicular to the magnetic field, are identified. Much of the paper deals with the more restricted problem in which f is specified as a bi-Maxwellian over a straight line of finite length in the equatorial plane of the dipole and perpendicular to field lines. This might be thought of as specifying a cross-tail ion injection source; our formalism then describes the subsequent spatial development. The distribution away from the source is a scaled bi-Maxwellian but one that is cut off at large and small kinetic energies, which depend on position. Density and pressure components are reduced from the values they would have if the total content of individual flux tubes convected intact. The equatorial and meridional variations of density and pressure components are examined and compared systematically for the isotropic and highly anisotropic situations. There appears to be little qualitative difference due to anisotropy. An anisotropy measure is defined, and its spatial variation determined as a signature of possible MHD instability. Extreme values are found, larger than at the source, but the plasma beta in such regions is probably so low as to render the effect inconsequential energetically. Finally, the possible consequence of 'nonadia- batic' pressure profiles on electrostatic interchanges is considered, and a boundary delineating stabilizing and destabilizing regions determined.

Huang, T. S.↗
NASA NTRS1973

Observations of collisionless drift waves.

Velocity distribution functions of both the electron and the proton component of the magnetospheric plasma are measured in 62 logarithmically spaced steps from 50 eV to 50 keV by an instrument carried upon the ATS-5 spacecraft in circular synchronous orbit (6.6 earth radii). Oscillations which appear to be collisionless drift waves having periods of several minutes or longer are found in this data. Linearized wave theory can be used to predict the theoretical perturbation distribution function in terms of the perturbing fields and the equilibrium distribution function. The functional dependence of the theoretical perturbation distribution function upon particle energy can then be compared with that of the measured perturbation.

Laquey, R. E.↗
NASA NTRS1975

Plasma-sprayed, self-lubricating coatings for use from cryogenic temperatures to 870 deg C (1600 deg F)

A plasma-sprayed coating is described with good lubricating properties over a wide temperature range. The coating, designated NASA LUBE PS101, contains silver, nichrome, calcium fluoride, and an oxidation protective glass. Oscillating tests were conducted of self-aligning, plain cylindrical bearings, in which the bore was lined with 0.025 cm (0.010 in.) thick coatings of PS101; these were conducted at a radial load of 3.5 x 10 to the 7th power N/sq m (5000 psi) in nitrogen gas at -107 C (-160 F), in vacuum at room temperature, and in air from room temperature to 870 C (1600 F). Friction coefficients were less than 0.25 in all cases and wear rates were low. The coating is not brittle, and it has adequate oxidation resistance in air to at least 870 C.

Sliney, H. E.↗
DOE OSTI2024

Overview of physics results from the ADITYA-U tokamak and future experiments

The ADITYA upgrade (ADITYA-U), a medium-sized (R 0 = 75 cm, a = 25 cm) conventional tokamak facility in India, has been consistently producing experiments findings by usingcircular and shaped-plasmas. Recognizing the plasma parameters aligning closely with the design parameters of circular limited plasmas, ADITYA-U shifted its focus toward exploring the operational regime for experimentation on saw-tooth and MHD phenomena. Moreover, ADITYA-U has made consistent advancements toward conducting preliminary plasma shaping experiments through the activation of top and bottom divertor coils utilizing hydrogen as well as deuterium fuels. Confinement is improved by a factor of ~1.5 in D 2 plasmas when compared to H 2 plasmas of ADITYA-U. Further, ADITYA-U operations emphasize preventing disruptions and runaway electrons (REs) to ensure safe operations for future fusion devices. Significant suppression of REs has been achieved in ADITYA-U with the application of pulsed localized vertical magnetic field (LVF) perturbation, thereby establishing the technique's independence from the tokamak device. The successful RE mitigation requires a critical threshold of LVF pulse magnitude, which is approximately 1% of the toroidal magnetic field, and a minimum duration of ~5 ms. Apart from this, several novel findings have been achieved in the ADITYA-U experiments, including the modification of sawtooth duration through gas-puff, the emergence of MHD-induced geodesic acoustic mode-like oscillations, the propagation of fast heat pulses induced by MHD activity, the control of RE dynamics through Gas-puffs, the propagation of pinch-driven cold-pulses, the transport and core accumulations of argon impurities, the mass dependency of plasma toroidal rotation and the detection of 'RICE' scaling, as well as the characterization of edge plasma using wall conditioning methods, such as glow discharge cleaning using a combination of Ar-H 2 mixture, localized wall cleaning by electron cyclotron resonant plasma, and the development of machine learning-based disruption predictions, will be discussed in this paper.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Coherent homodyne detection for amplified cross-beam electric-field induced second harmonic

The electric-field induced second harmonic (E-FISH) signal sensing is commonly used as a nonlinear optical technique to probe electric fields inside a plasma region. Cross-beam E-FISH is being investigated to improve spatial resolution by defining the interaction volume via a controlled geometry of two overlapping noncolinear optical beams. This drastic reduction in interaction length of the electric field and laser region results in a significant signal reduction. Here, to overcome this signal reduction, we introduce coherent amplification of the cross-beam E-FISH signal by mixing the low E-FISH signal with a phase-locked bright local oscillator. We demonstrate enhancement of the signal. By introducing a local oscillator we can now derive the polarity of the measured electric field through the phase of the homodyne signal. To illustrate the technique, we, for the first time, to the best of our knowledge, measure the magnitude and the direction of the electric field in a cold atmospheric pressure plasma jet, which dynamically follows the profile of the applied bias current.

42 ENGINEERING↗
NASA NTRS1979

Satellite observations of the spatial extent and structure of Pc 3, 4, 5 pulsations near the magnetospheric equator

Simultaneous observations of Pc 3, 4, 5 pulsations by five satellites in the pre-noon local time sector at and near synchronous orbit are examined. The periods of these simultaneous pulsations are not the same at the different observation points. This difference is attributed to site dependent resonant conditions. The spatial properties of the temporal phenomenon are demonstrated with observations by ISEE-1 and -2 as they pass through oscillations in a spatially limited region. Fundamental and second harmonic standing Alfven waves are observed simultaneously on the same field line. The periods are consistent with model predictions when the measured plasma composition, which by mass consists mainly of singly ionized oxygen, is taken into account.

Singer, H. J.↗
NASA NTRS1981

Calculation and observation of thermal electrostatic noise in solar wind plasma

Calculations, both approximate algebraic and numerical, have been carried out for the noise due to electrostatic waves incident on a dipole antenna. The noise is calculated both for a thermal equilibrium plasma, and one having several components at different temperatures. The results are compared with measurements from the IMP-6 satellite. In various frequency ranges, the noise power is dominated by Langmuir oscillations, by electron acoustic waves and by ion acoustic waves. The measurements are consistent with all of these, although the ion waves are not definitely observed, due to interference from shot noise.

Kellogg, P. J.↗
NASA NTRS2004

Large-Scale Alfvenic Impulses on the Sun: How They Are Generated and What We Learn From Them

NASA GSFC The Sun's atmosphere hosts a wide variety of magnetosonic disturbances. These wave modes are detected, almost exclusively, by examining images of the Sun's magnetic atmosphere and looking for propagating distortions. Although none of the Sun's plasma parameters are measured directly, we derive a great deal of information from these observations. In fact, by modeling these propagating disturbances, we may be able to derive the most accurate estimates plasma parameters. From observations absorption, refraction, reflection, and coupling of numerous wave modes, we advance our knowledge of the Sun's magnetic field, temperature, density, and current. The Sun's continuous oscillation, coronal mass ejections, flares, and other dynamic phenomena can produce wave disturbances which are observable from near-Earth space. Several of these disturbances have been traced from the inner corona out into the heliosphere. From the generation of these disturbances, we are able to learn about the phenomena which create them as well as the media through which they re-propagating. The presentation will include a discussion of the generation of Alfvenic disturbances on the Sun, ways we observe these disturbances, and how recent advances in modeling and analysis have brought us closer to determining solar in situ parameters.

Thompson, Barbara↗
NASA NTRS1983

Cold streams of ionospheric oxygen in the plasma sheet during the CDAW-6 event of March 22, 1979

During magnetospheric substorm events, the plasma and ion composition experiments in the ISEE-1 and 2 satellites detected cold ionospheric O+ streams, moving tailwards in the near Earth magnetotail. Flow is parallel to the magnetic field lines, with drift velocity in agreement with the electric field topology obtained by mapping the model ionospheric field along the magnetic field lines. Fluctuations of the flow velocity of the streams can be related to magnetotail movements. Oscillations of the flow direction and speed with periods ranging from 5 to 10 min that suggest the presence of waves are observed. The streams are observed at all distances between 15 and 6 Re from the Earth. When averaged over 360 deg, the streams show up as a low energy peak, superimposed on the distribution of isotropic plasma sheet ions. This double-peak structure of the energy spectrum seems typical of the disturbed plasma sheet.

Orsini, S.↗
NASA NTRS1985

Cold streams of ionospheric oxygen in the plasma sheet during the CDAW 6 event of March 22, 1979

During magnetospheric substorm events, the plasma and ion composition experiments in the ISEE-1 and 2 satellites detected cold ionospheric O+ streams, moving tailwards in the near earth magnetotail. Flow is parallel to the magnetic field lines, with drift velocity in agreement with the electric field topology obtained by mapping the model ionospheric field along the magnetic field lines. Fluctuations of the flow velocity of the streams can be related to magnetotail movements. Oscillations of the flow direction and speed with periods ranging from 5 to 10 min that suggest the presence of waves are observed. The streams are observed at all distances between 15 and 6 Re from the earth. When averaged over 360 deg, the streams show up as a low energy peak, superimposed on the distribution of isotropic plasma sheet ions. This double-peak structure of the energy spectrum seems typical of the disturbed plasma sheet.

Orsini, S.↗
DOE OSTI2022

Inviscid damping of an elliptical vortex subject to an external strain flow

Inviscid spatial Landau damping is studied experimentally for the case of oscillatory motion of a two-dimensional vortex about its elliptical equilibrium in the presence of an applied strain flow. Here, the experiments are performed using electron plasmas in a Penning–Malmberg trap. They exploit the isomorphism between the two-dimensional Euler equations for an ideal fluid and the drift-Poisson equations for the plasma, where plasma density is the analog of vorticity. Perturbed elliptical vortex states are created using E x B strain flows, which are generated by applying voltages to electrodes surrounding the plasma. Measurements of spatial Landau damping (also called critical-layer damping) are in agreement with previous studies in the absence of an applied strain, where the damping is due to a resonance between the local fluid motion and the vortex oscillations. Interestingly, the damping rate does not change significantly over a wide range of applied strain rates. This can be accurately predicted from the initial vorticity profile, even though the resonant frequency is reduced substantially due to the applied strain. For higher amplitude perturbations, nonlinear trapping oscillations also exhibit behavior similar to the strain-free case. In principle, higher-order effects of the applied strain, such as separatrix crossing of peripheral vorticity and interactions with harmonics of the fundamental resonance, are expected to change the damping rate. However, this occurs only for conditions that are not realized in the experiments described here. Vortex-in-cell simulations are used to investigate the possible roles of these effects.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Constraining the phase shift of relativistic species in DESI BAOs

In the early Universe, neutrinos decouple quickly from the primordial plasma and propagate without further interactions. The impact of free-streaming neutrinos is to create a temporal shift in the gravitational potential that impacts the acoustic waves known as baryon acoustic oscillations (BAOs), resulting in a non-linear spatial shift in the Fourier-space BAO signal. In this work, we make use of and extend upon an existing methodology to measure the phase shift amplitude $\beta _{\phi }$ and apply it to the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1) BAOs with an anisotropic BAO fitting pipeline. We validate the fitting methodology by testing the pipeline with two publicly available fitting codes applied to highly precise cubic box simulations and realistic simulations representative of the DESI DR1 data. We find further study towards the methods used in fitting the BAO signal will be necessary to ensure accurate constraints on $\beta _{\phi }$ in future DESI data releases. Using DESI DR1, we present individual measurements of the anisotropic BAO distortion parameters and the $\beta _{\phi }$ for the different tracers, and additionally a combined fit to $\beta _{\phi }$ resulting in $\beta _{\phi } = 2.7 \pm 1.7$. After including a prior on the distortion parameters from constraints using Planck we find $\beta _{\phi } = 2.7^{+0.60}_{-0.67}$ suggesting $\beta _{\phi } > 0$ at 4.3$\sigma$ significance. This result may hint at a phase shift that is not purely sourced from the standard model expectation for $N_{\rm {eff}}$ or could be a upwards statistical fluctuation in the measured $\beta _{\phi }$; this result relaxes in models with additional freedom beyond Lambda-cold dark matter.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1985

Submillimeter local oscillators for spaceborne heterodyne applications

Existing and prospective submillimeter local oscillator technologies are surveyed and compared with respect to criteria of suitability for application in spaceborne submillimeter heterodyne receivers as those proposed for the Large Deployable Reflector (LDR). Solid-state and plasma devices are considered in terms of fundamental limitations.

Petuchowski, S. J.↗
DOE OSTI2021

Experimental evidence of runaway electron tail generation via localized helical structure in pellet-triggered tokamak disruptions

A novel detector, using stacked BGO crystals, is developed for runaway electron (REs) studies in the DIII-D tokamak. It is able to resolve fast dynamics of high-energy tail formation of REs with an ultra-high time resolution of ~1 μs. As a cost, the detector estimates the `effective' energy of a given shape of γ-ray spectra and sacrifices the energy resolution. In aid of the new measurement capability, a rapid, inhomogeneous growth of RE tail is observed in detail during a major disruption triggered by an argon pellet. It is found that both the population and energy of a well-confined RE tail significantly oscillate at the early period of the growth. The oscillation phase is locked to a slow rotating magnetohydrodynamic instability, which is briefly destabilized for only ~1 ms at the early period of the current quench. The oscillation ceases promptly, when the mode disappears. As a result, the data suggests that the high-energy RE tail is well-confined and accelerated via a localized helical structure in the plasma core.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗