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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Filamentation and focusing of electron beams due to interactions with plasma waves

Results of numerical modeling of the interaction of an electron beam propagating across relativistic plasma waves indicate that electron beam filamentation and focusing may occur under certain conditions. The model is based on solving the relativistic equation of motion in three dimensions for the individual electrons in a tenuous Gaussian beam, as they pass through a relativistic plasma wave. Several electron beam and plasma wave parameters were varied, and the results are summarized. One of the results is that the spacing of the electron beam filaments correlates with the wavelength of the plasma wave. The electron beam filaments appear as vertical slabs after the beam exits the plasma waves. The electron beam also compresses to a focus after it exits the plasma, and the focal distance depends on several parameters including the electron beam energy and phase velocity of the relativistic plasma wave. It is suggested that these focusing and filamentation phenomena may be the basis for diagnostics schemes for laser plasma interactions. The parameters used in the model were electron beam energies in the 5–50 keV range and plasma wave properties typical for the beat-wave produced by CO2 lasers, which correspond to the facilities available in our laboratory. The limitations of these results to lower energy density beam and plasma regimes and to higher energy density regimes will be discussed.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Evolution of intermittent filaments in the scrape-off layer of NSTX

Filamentary structures naturally arise from background turbulence in the scrape-off layer (SOL) of plasmas, leading to significant particle and heat transport that can degrade overall plasma confinement. This enhanced transport can contribute to unacceptably high heat loads on plasma-facing components. As such, understanding the physics of SOL plasma filaments is critical for predicting and mitigating their effects in future fusion devices. On the National Spherical Torus Experiment (NSTX), plasma filaments—commonly referred to as “blobs”—were investigated using the gas-puff imaging (GPI) diagnostic in the edge and SOL regions. The analysis involved identifying, segmenting, and tracking the characteristic contours of the blobs in each frame of the GPI video sequences. Their evolution was characterized through shape descriptors, velocity, and angular velocity derived from their contour coordinates. The results indicate that as the blob area increases, their shapes become more concave and less circular, suggesting reduced structural stability in larger blobs. This result aligns with previous theoretical results where it was shown that larger blobs are more susceptible to instabilities [Krasheninnikov et al., J. Plasma Phys. 74, 679–717 (2008) and D'Ippolito et al., Phys. Plasmas 18, 060501 (2011)]. A positive correlation was observed between radial velocity and radial position, suggesting radially outward acceleration of the filaments, potentially driven by decreasing viscous drag toward the far SOL. Interestingly, blobs in background SOL turbulence exhibited minimal spinning in contrast to filaments originating from edge localized modes, which show substantial rotation during their paths [Lampert et al., Phys. Plasmas 29, 102502 (2022)]. Statistical analysis of the solidity and total curvature shape descriptors, along with their temporal evolution, revealed relatively broad, near-Gaussian distributions. This suggests that blob morphology is strongly influenced by stochastic turbulent processes in the surrounding plasma environment. Blob parameters were also compared with bulk plasma and radial profile measurements. Notable trends were found between blob rotation and poloidal velocity with collisionality and line-integrated density. These findings contribute to a deeper understanding of blob dynamics and provide valuable insights for refining SOL turbulence models.

Covariance and correlation↗
DOE OSTI2016

Periodic colour-centre structure formed under filamentation of mid-IR femtosecond laser radiation in a LiF crystal

A colour-centre structure formed in a LiF crystal under filamentation of a femtosecond mid-IR laser pulse with a power slightly exceeding the critical power for self-focusing has been experimentally and theoretically investigated. Strictly periodic oscillations have been detected for the first time for the density of the colour centres induced in an isotropic LiF crystal under filamentation of a laser beam with a wavelength tuned in the range from 2600 to 3350 nm. The structure period is found to be about 30 μm. With an increase in the laser radiation wavelength, the period of the oscillations decreases and their amplitude increases. The maximum colour centre density, observed under filamentation of a 3100-nm beam, is related to the increased contribution of the direct generation of colour centres as a result of the absorption of an integer number of photons by the exciton band. It is numerically shown that the formation of a periodic colour-centre structure in LiF is due to the periodic change in the light field amplitude in the light bullet (1.5 optical periods long) formed under filamentation. (extreme laser radiation: physics and fundamental applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Post-filamentation propagation of high-power laser pulses in air in the regime of narrowly focused light channels

We report the results of experimental and theoretical studies of the post-filamentation stage of nonlinear propagation of high-power pulsed radiation from a Ti : sapphire laser in air. We have for the first time obtained the experimental dependences of the angular divergence of specific spatially localised high-intensity light structures that are observed in the beam after its multiple filamentation (post-filamentation of channels) when varying the initial focusing of laser radiation and its energy. It is found that the angular divergence of the post-filamentation channels decreases with increasing pulse energy and reducing beam numerical aperture. The experimental dependences are qualitatively interpreted based on the diffraction model of the Bessel – Gaussian beam. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Resonant wave–filament interactions as a loss mechanism for HHFW heating and current drive

Abstract Perkins et al (2012 Phys. Rev. Lett. 109 045001) reported unexpected power losses during high harmonic fast wave (HHFW) heating and current drive in the National Spherical Torus Experiment (NSTX). Recently, Tierens et al (2020 Phys. Plasmas 27 010702) proposed that these losses may be attributable to surface waves on field-aligned plasma filaments, which carry power along the filaments, to be lost at the endpoints where the filaments intersect the limiters. In this work, we show that there is indeed a resonant loss mechanism associated with the excitation of these surface waves, and derive an analytic expression for the power lost to surface wave modes at each filament.

Tierens, W. (ORCID:0000000269798140)↗
DOE OSTI2021

The combined application of the anti- RAS1 and anti- RIM101 2'- O MethylRNA oligomers enhances Candida albicans filamentation control

Abstract Although antisense oligomers (ASOs) have been successfully utilized to control gene expression, they have been little exploited to control Candida albicans virulence's determinants. Filamentation is an important virulence factor of C. albicans, and RAS1 and RIM101 genes are involved in its regulation. Thus, the main goal of this work was to project ASOs, based on 2'-OMethyl chemical modification, to target RAS1 and RIM101 mRNA and to validate its application either alone or in combination, to reduce Candida filamentation in different human body fluids. It was verified that both, anti-RAS1 2'OMe and anti-RIM101 2'OMe oligomers, were able to reduce the levels of RAS1 and RIM101 genes’ expression and to significantly reduce C. albicans filamentation. Furthermore, the combined application of anti-RAS1 2'OMe oligomer and anti-RIM101 2'OMe oligomer enhances the control of C. albicans filamentation in artificial saliva and urine. Our work confirms that ASOs are useful tools for research and therapeutic development on the control of candidiasis.

Barbosa, Ana↗
DOE OSTI2019

On the nature of radio filaments near the Galactic Centre

We suggest that narrow, long radio filaments near the Galactic Centre arise as kinetic jets – streams of high-energy particles escaping from ram pressure confined pulsar wind nebulae (PWNe). The reconnection between the PWN and interstellar magnetic field allows pulsar wind particles to escape, creating long narrow features. They are the low-frequency analogues of kinetic jets seen around some fast-moving pulsars, such as The Guitar and The Lighthouse PWNe. The radio filaments trace a population of pulsars also responsible for the Fermi GeV excess produced by the Inverse Compton scattering by the pulsar wind particles. The magnetic flux tubes are stretched radially by the large-scale Galactic winds. In addition to PWNe accelerated particles can be injected at supernovae remnants. The model predicts variations of the structure of the largest filaments on scales of ~dozens of years – smaller variations can occur on shorter time-scales. We also encourage targeted observations of the brightest sections of the filaments and of the related unresolved point sources in search of the powering PWNe and pulsars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Cosmic filaments from cosmic strings

Cosmic strings are generically predicted in many extensions of the Standard Model of particle physics. In this work, we propose a new avenue for detecting cosmic strings through their effect on the filamentary structure in the cosmic web. Using cosmological simulations of the density wake from a cosmic string, we examine a variety of filament structure probes. We show that the largest effect of the cosmic string is an overdensity in the filament distribution around the string wake. The signal from the overdensity is stronger at higher redshift and more robust with a wider field. We analyze the spatial distribution of filaments from a publicly available catalog of filaments built from Sloan digital sky survey galaxies. With existing data, we find no evidence for the presence of a cosmic string wake with string tension parameter $\textit{Gμ}$ above 5 × 10 –6 . However, we project WFIRST will be able to detect a signal from such a wake at the 99% confidence level at redshift $\textit{z}$ = 2, with significantly higher confidence and the possibility of probing lower tensions ($\textit{Gμ}$ ~ 10 –6 ), at $\textit{z}$ = 10. The sensitivity of this method is not competitive with constraints derived from the cosmic microwave background. However, it provides an independent discovery channel at low redshift, which could be a smoking gun in scenarios in which the cosmic microwave background bound can be weakened.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Optical Imaging of Laser-Driven Fast Electron Weibel-like Filamentation in Overcritical Density Plasma

We report on the measurement of filamented transport of laser-generated fast electron beams in near-critical density plasma. A relativistic intensity long-wave-infrared laser irradiated a hydrodynamically shaped helium gas flow at an electron density n e ≃ 10 25 m − 3 , generating a large flux of fast electrons that propagated beyond the critical surface. The beam-to-background electron density ratio was sufficiently high to drive growth of Weibel-like filamentation, which was measured by optical probing to extend up to 800 μ m with radii ∼ 10 μ m . Particle-in-cell simulations reproduce the main features of the filamentation generation, suggesting that collisionless processes are dominant in these interactions. Expansion of the filaments after formation infers a fast electron heated plasma temperature ∼ 400 eV in the overcritical density plasma. Published by the American Physical Society 2025

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Filamentation of long-wave infrared pulses in the atmosphere

Filamentation of a high-power laser beam in air opens possibility of the diffraction-compensated propagation of a laser beam over long distances and as such is being considered for remote stand-off detection, lightning control, free-space communications, and long-range projection of high-energy pulses. Switching to long-wave infrared (LWIR) range for filamentation, as shown in recent experiments, allows for generation of a single centimeter-diameter channel in air that, in comparison with a short-wavelength laser filament, has four orders of magnitude larger cross-section and guides many Joules of pulse energy over multiple Rayleigh distances at a clamped intensity of ~10 12 W/cm 2 . Self-guiding of LWIR pulses in air arises from the balance between self-focusing, diffraction and defocusing caused by free carriers generated via many-body Coulomb induced ionization which effectively decrease the molecular polarizability during the long-wavelength laser pulse. Understanding where this new ionization regime plays a role, below the threshold of the well adopted single-atom tunnel ionization in gases, could became a new frontier in strong-field interactions. Here, this paper offers an overview of the atmospheric filamentation research at long-wave infrared wavelengths.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Plasma temperature clamping in filamentation laser induced breakdown spectroscopy

Ultrafast laser filament induced breakdown spectroscopy is a very promising method for remote material detection. We present characteristics of plasmas generated in a metal target by laser filaments in air. Our measurements show that the temperature of the ablation plasma is clamped along the filamentation channel due to intensity clamping in a filament. Nevertheless, significant changes in radiation intensity are noticeable, and this is essentially due to variation in the number density of emitting atoms. The present results also partly explains the reason for the occurrence of atomic plume during fs LIBS in air compared to long-pulse ns LIBS.

2D fast imaging↗
DOE OSTI2016

COLD MILKY WAY H i GAS IN FILAMENTS

We investigate data from the Galactic Effelsberg-Bonn H i Survey, supplemented with data from the third release of the Galactic All Sky Survey (GASS III) observed at Parkes. We explore the all-sky distribution of the local Galactic H i gas with |v{sub LSR}|<25 km s{sup −1} on angular scales of 11′–16′. Unsharp masking is applied to extract small-scale features. We find cold filaments that are aligned with polarized dust emission and conclude that the cold neutral medium (CNM) is mostly organized in sheets that are, because of projection effects, observed as filaments. These filaments are associated with dust ridges, aligned with the magnetic field measured on the structures by Planck at 353 GHz. The CNM above latitudes |b|>20{sup ∘} is described by a log-normal distribution, with a median Doppler temperature T{sub D} = 223 K, derived from observed line widths that include turbulent contributions. The median neutral hydrogen (H i) column density is N{sub H i} ≃ 10{sup 19.1} cm{sup −2}. These CNM structures are embedded within a warm neutral medium with N{sub H i} ≃ 10{sup 20} cm{sup −2}. Assuming an average distance of 100 pc, we derive for the CNM sheets a thickness of ≲0.3 pc. Adopting a magnetic field strength of B{sub tot} = (6.0 ± 1.8) μG, proposed by Heiles and Troland, and assuming that the CNM filaments are confined by magnetic pressure, we estimate a thickness of 0.09 pc. Correspondingly, the median volume density is in the range 14 ≲ n ≲ 47 cm{sup −3}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Massive quiescent cores in orion. VI. The internal structures and a candidate of transiting core in NGC 2024 filament

We present a multiwavelength observational study of the NGC 2024 filament using infrared to submillimeter continuum and the NH{sub 3} (1,1) and (2,2) inversion transitions centered on FIR-3, the most massive core therein. FIR-3 is found to have no significant infrared point sources in the Spitzer/IRAC bands. But the NH{sub 3} kinetic temperature map shows a peak value at the core center with T{sub k}=25 K, which is significantly higher than the surrounding level (T{sub k} = 15–19 K). Such internal heating signature without an infrared source suggests an ongoing core collapse possibly at a transition stage from first hydrostatic core (FHSC) to protostar. The eight dense cores in the filament have dust temperatures between 17.5 and 22 K. They are much cooler than the hot ridge (T{sub d}∼55 K) around the central heating star IRS-2b. Comparison with a dust heating model suggests that the filament should have a distance of 3–5 pc from IRS-2b. This value is much larger than the spatial extent of the hot ridge, suggesting that the filament is spatially separated from the hot region along the line of sight.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

RELATIONSHIP BETWEEN DISTRIBUTION OF MAGNETIC DECAY INDEX AND FILAMENT ERUPTIONS

The decay index n of a horizontal magnetic field is considered to be an important parameter in judging the stability of a flux rope. However, the spatial distribution of this parameter has not been extensively explored so far. In this paper, we present a delineative study of the three-dimensional maps of n for two eruptive events, in which filaments underwent asymmetrical eruptions. The corresponding n -distributions are both found to show that the filaments tend to erupt at abnormal regions (dubbed ABN regions) of n . These ABN regions appear to be divided into two subregions, with larger and smaller n . Moreover, an analysis of the magnetic topological configuration of the ABN regions has been also performed. The results indicate that these ABN regions are associated with a kind of special quasi-separatrix layer across which the connectivity of magnetic field is discontinuous. The presented observations and analyses strongly suggest that the torus instability in ABN regions may play a crucial role for the triggering of an asymmetrical eruption. Additionally, our investigation can provide a way of forecasting how a filament might erupt, and predicting the location for an asymmetrically eruptive filament to be split through analyzing the spatial structure of n .

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The tidal filament of NGC 4660

NGC 4660, in the Virgo cluster, is a well-studied elliptical galaxy which has a strong disk component (D/T approximately 0.2–0.3). The central regions, including the disk component, have stellar populations approximately 12–13 Gyr in age, based on SAURON studies. However, we report the discovery of a long, narrow tidal filament associated with the galaxy, as seen in deep co-added Schmidt plate images and deep CCD frames, implying that the galaxy has undergone a tidal interaction and merger within the last few Gyr. The relative narrowness of the filament implies a wet merger with at least one spiral galaxy involved, but the current state of the system shows little evidence of such. However, a two-component photometric fit using GALFIT shows much bluer B−V colors for the disk component than for the elliptical component, which may represent a residual trace of enhanced star formation in the disk caused by the interaction 1–2 Gyr ago. There are brighter concentrations within the filament that resemble tidal dwarf galaxies, although they are at least 40 times fainter. These concentrations may represent faint, evolved versions of those galaxies. A previously detected stripped satellite galaxy south of the nucleus seen in our residual image may imply that the filament is a tidal stream produced by perigalactic passages of this satellite.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Great Solar Active Region NOAA 12192: Helicity Transport, Filament Formation, and Impact on the Polar Field

The solar active region (AR), NOAA 12192, appeared in 2014 October as the largest AR in 24 years. Here we examine the counterintuitive nature of two diffusion-driven processes in the region: the role of helicity buildup in the formation of a major filament, and the relationship between the effects of supergranular diffusion and meridional flow on the AR and on the polar field. Quantitatively, calculations of current helicity and magnetic twist from Helioseismic and Magnetic Imager (HMI) vector magnetograms indicate that, though AR 12192 emerged with negative helicity, positive helicity from subsequent flux emergence, consistent with the hemispheric sign-preference of helicity, increased over time within large-scale, weak-field regions such as those near the polarity inversion line (PIL). Morphologically, Atmospheric Imaging Assembly observations of filament barbs, sigmoidal patterns, and bases of Fe xii stalks initially exhibited signatures of negative helicity, and the long filament that subsequently formed had a strong positive helicity consistent with the helicity buildup along the PIL. We find from full-disk HMI magnetograms that AR 12192's leading positive flux was initially closer to the equator but, owing either to the region’s magnetic surroundings or to its asymmetric flux density distribution, was transported poleward more quickly on average than its trailing negative flux, contrary to the canonical pattern of bipole flux transport. This behavior caused the AR to have a smaller effect on the polar fields than expected and enabled the formation of the very long neutral line where the filament formed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

X Marks the Spot: Nexus of Filaments, Cores, and Outflows in a Young Star-forming Region

We present a multiwavelength investigation of a region of a nearby giant molecular cloud that is distinguished by a minimal level of star formation activity. With our new {sup 12}CO(J = 2–1) and {sup 13}CO(J = 2–1) observations of a remote region within the middle of the California molecular cloud, we aim to investigate the relationship between filaments, cores, and a molecular outflow in a relatively pristine environment. An extinction map of the region from Herschel Space Observatory observations reveals the presence of two 2 pc long filaments radiating from a high-extinction clump. Using the {sup 13}CO observations, we show that the filaments have coherent velocity gradients and that their mass-per-unit-lengths may exceed the critical value above which filaments are gravitationally unstable. The region exhibits structure with eight cores, at least one of which is a starless, prestellar core. We identify a low-velocity, low-mass molecular outflow that may be driven by a flat spectrum protostar. The outflow does not appear to be responsible for driving the turbulence in the core with which it is associated, nor does it provide significant support against gravitational collapse.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Hub-filament System in IRAS 05480+2545: Young Stellar Cluster and 6.7 GHz Methanol Maser

To probe the star formation (SF) process, we present a multi-wavelength study of IRAS 05480+2545 (hereafter I05480+2545). Analysis of Herschel data reveals a massive clump (M {sub clump} ∼ 1875 M{sub ⊙}; peak N(H{sub 2}) ∼ 4.8 × 10{sup 22} cm{sup −2}; A {sub V} ∼ 51 mag) containing the 6.7 GHz methanol maser and I05480+2545, which is also depicted in a temperature range of 18–26 K. Several noticeable parsec-scale filaments are detected in the Herschel 250 μm image and seem to be radially directed to the massive clump. It resembles more of a “hub-filament” system. Deeply embedded young stellar objects (YSOs) have been identified using the 1–5 μm photometric data, and a significant fraction of YSOs and their clustering are spatially found toward the massive clump, revealing the intense SF activities. An infrared counterpart (IRc) of the maser is investigated in the Spitzer 3.6–4.5 μm images. The IRc does not appear as a point-like source and is most likely associated with the molecular outflow. Based on the 1.4 GHz and Hα continuum images, the ionized emission is absent toward the IRc, indicating that the massive clump harbors an early phase of a massive protostar before the onset of an ultracompact H ii region. Together, the I05480+2545 is embedded in a very similar “hub-filament” system to those seen in the Rosette Molecular Cloud. The outcome of the present work indicates the role of filaments in the formation of the massive star-forming clump and cluster of YSOs, which might help channel material to the central hub configuration and the clump/core.

79 ASTRONOMY AND ASTROPHYSICS↗