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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Ultrasound-Assisted Nonthermal, Nonequilibrium Separation of Organic Molecules from Their Binary Aqueous Solutions: Effect of Solute Properties on Separation

The separation of organic molecules in downstream processes, such as distillation, plays a vital role in biobased chemical production. A comprehensive study was performed here using ultrasonic energy to separate 11 organic molecules from their binary aqueous solutions under nonthermal, nonequilibrium, and phase-change free conditions. A batch sonoseparator with a three-stage mist collection unit allowed direct analysis of ultrasound-generated mist with an HPLC/GC and differentiation and quantification of the vapor and mist. The results showed that the alcohols (1-butanol, ethanol, 1-propanol, and methanol) and acetone were enriched in the ultrasound-generated mist with enrichment ratios of 3.2–5. On the other hand, ethylene glycol, glycerol, γ-valerolactone (GVL), glucose, and sucrose were diluted with dilution ratios in the range of 2.04–15.7 in the mist and vapor generated by ultrasound (or concentrated in the bulk solution). No enrichment nor dilution of acetic acid was observed. The role of various physicochemical parameters such as dynamic viscosity, surface tension, Henry’s law of solubility constant, vapor pressure, and octanol–water partition coefficient in the enrichment was examined. Furthermore, the hydrophobicity of the organic molecules represented by the octanol–water partition coefficient was found to play a crucial role in determining the separation characteristics of the molecules in ultrasound-generated mist and vapor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2023

Prospects of Detecting Nonthermal Protons in Solar Flares via Lyman Line Spectroscopy: Revisiting the Orrall-Zirker Effect

Solar flares are efficient particle accelerators, with a substantial fraction of the energy released manifesting as nonthermal particles. While the role that nonthermal electrons play in transporting flare energy is well studied, the properties and importance of nonthermal protons are rather less well understood. This is in large part due to the paucity of diagnostics, particularly at the lower-energy (deka-keV) range of nonthermal proton distributions in flares. One means to identify the presence of deka-keV protons is by an effect originally described by Orrall & Zirker. In the Orrall–Zirker effect, nonthermal protons interact with ambient neutral hydrogen, and via charge exchange produce a population of energetic neutral atoms (ENAs) in the chromosphere. These ENAs subsequently produce an extremely redshifted photon in the red wings of hydrogen spectral lines. We revisit predictions of the strength of this effect using modern interaction cross sections, and numerical models capable of self-consistently simulating the flaring nonequilibrium ionization stratification, and the nonthermal proton distribution (and, crucially, their feedback on each other). We synthesize both the thermal and nonthermal emission from Ly α and Ly β, the most promising lines that may exhibit a detectable signal. These new predictions are weaker and more transient than prior estimates, but the effects should be detectable in fortuitous circumstances. We degrade the Ly β emission to the resolution of the Spectral Imaging of the Coronal Environment (SPICE) instrument on board Solar Orbiter, demonstrating that though likely difficult, it should be possible to detect the presence of nonthermal protons in flares observed by SPICE.

Solar flares↗
NASA NTRS1986

Hard X-ray imaging and the relative contribution of thermal and nonthermal emission in flares

The question of whether the impulsive 25 to 100 keV X-ray emission from solar flares is thermal or nonthermal has been a long-standing controversy. Both thermal and nonthermal (beam) models have been developed and applied to the hard X-ray data. It now seems likely that both thermal and nonthermal emission have been observed at hard X-ray energies. The Hinotori classification scheme, for example, is an attempt to associate the thermal-nonthermal characteristics of flare hard X-ray emission with other flare properties. From a theoretical point of view, it is difficult to generate energetic, nonthermal electrons without dumping an equal or greater amount of energy into plasma heating. On the other hand, any impulsive heating process will invariably generate at least some nonthermal particles. Hence, strictly speaking, although thermal or nonthermal emission may dominate the hard X-ray emission in a given energy range for a given flare, there is no such thing as a purely thermal or nonthermal flare mechanism.

Holman, G. D.↗
NASA NTRS2007

Motion of 3-6 keV Nonthermal Sources Along the Legs of a Flare Loop

Observations of nonthermal X-ray sources me critical to studying electron acceleration and transport in solar flares. Strong thermal emission radiated from the preheated plasma before the flare impulsive phase often makes it difficult to detect low-energy X-ray sources that are produced by relatively low-energy nonthermal electrons. Knowledge of the distribution of these low-energy nonthermal electrons is particularly important in determining the total nonthermal electron energy in solar flares. We report on an 'early impulsive flare' in which impulsive hard X-ray emission was seen early in the flare before the soft X-ray emission had risen significantly, indicating limited plasma pre-heating. Early in the flare, RHESSI < 25 keV images show coronal sources that moved first downward and then upwards along the legs of a flare loop. In particular, the 3-6 keV source appeared as a single coronal source at the start of the flare, and then it involved into two coronal sources moving down along the two legs of the loop. After nearly reaching the two footpoints at the hard X-ray peak, the two sources moved back up to the looptop again. RHESSI images and light curves all indicate that nonthermal emission dominated at energies as low as 3-6 keV. We suggest that the evolution of both the spectral index and the low-energy cutoff of the injected electron distribution could result in the accelerated electrons reaching a lower altitude along the legs of the dense flare loop and hence result in the observed downward and upward motions of the nonthermal sources.

Sui, Linhui↗
NASA NTRS2016

Global Energetics of Solar Flares: Nonthermal Energies - Part III

This study entails the third part of a global flare energetics project, in which Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) data of 191 M and X-class flare events from the first 3.5 years of the Solar Dynamics Observatory mission are analyzed. We fit a thermal and a nonthermal component to RHESSI spectra, yielding the temperature of the differential emission measure (DEM) tail, the nonthermal power-law slope and flux, and the thermal nonthermal cross-over energy eco. From these parameters, we calculate the total nonthermal energy E(sub nt) in electrons with two different methods: (1) using the observed cross-over energy e(sub co) as low-energy cutoff, and (2) using the low-energy cut off e(sub wt) predicted by the warm thick-target bremsstrahlung model of Kontar et al. Based on a mean temperature of T(sub e) = 8.6 MK in active regions, we find low-energy cutoff energies of e(sub wt) = 6.2 +/-1.6 keV for the warm-target model, which is significantly lower than the cross-over energies e(sub co) = 21 +/- 6 keV. Comparing with the statistics of magnetically dissipated energies E(sub mag) and thermal energies E(sub th) from the two previous studies, we find the following mean (logarithmic) energy ratios with the warm-target model: E(sub nt) = 0.41E(sub mag), E(sub th) = 0.08 E(sub mag), and E(sub th) = 0.15 E(sub nt). The total dissipated magnetic energy exceeds the thermal energy in 95% and the nonthermal energy in 71% of the flare events, which confirms that magnetic reconnection processes are sufficient to explain flare energies. The nonthermal energy exceeds the thermal energy in 85% of the events, which largely confirms the warm thick-target model.

Aschwanden, Markus J.↗
DOE OSTI2026

Energetic Nonthermal Electrons within the Above-the-looptop Regions in Solar Flares: Acceleration, Feedback, and Quasiperiodic Pulsations

Solar flares are among the most dramatic events in the solar system, releasing substantial magnetic energy and accelerating a large number of electrons to high energies. Notably, in certain events, the above-the-looptop region may contain a significant population of nonthermal electrons, both in number and energy. For the first time, we adopt a novel numerical method that combines magnetohydrodynamics with energetic particles incorporating feedback from nonthermal electrons to investigate electron acceleration and transport in solar flares. We find that a large fraction of energetic electrons are accelerated via the current sheet and termination shock regions. Most energetic electrons are concentrated in the above-the-looptop region, carrying a sizable amount of the released energy. We observe that greater feedback of nonthermal electrons leads to steeper energy spectra. The energy density of the nonthermal electrons oscillates due to the periodic impact of magnetic islands into the above-the-looptop region, which may help explain the observed quasiperiodic pulsations. Our simulations provide new insights into the origin of nonthermal electrons and associated emissions in the above-the-looptop region.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2025

Nonthermal Velocities in a Solar Active Region Observed by SERTS

We present measurements of coronal nonthermal Doppler velocities in NOAA Active Region 7870 observed by the Solar EUV Research Telescope and Spectrograph during its 1995 sounding rocket flight (SERTS-95). The instrument included a multilayer-coated toroidal diffraction grating that enhanced its sensitivity in second order at wavelengths between about 171 and 225 Å. Analyses of spectra from this flight were previously published but did not address the issue of nonthermal velocities; we do so here for spectra averaged over the 123װ .8 segment of the slit for which the brightest portion of the region observed by SERTS was recorded. All emission lines are fit with Gaussian profiles. With post-flight laboratory spectra of He ii and Ne II-IIINe we derive a first-order instrumental width (full width at half-maximum intensity) of Finst,1 = 50.6 ± 3.1 mÅ and a second-order instrumental width of Finst,2 = 25.3 ±1.5 mÅ. For emission lines of Fe x−Fe xv, formed at 6.05 ≤ log T(K) ≤ 6.35, we find nonthermal velocities between 26.1 and 35.0 km s −1 , independent of temperature; this range corresponds to Vnonth = 30.6 ± 4.5 km s −1 . For the two unblended Fe xii lines at 192.394 and 193.509 Å closest to the maximum sensitivity of SERTS-95, we have Vnonth = 33.7 ± 1.3 km s −1 . When solar observations are used to derive or confirm instrumental widths for spectrometers in orbit, those observations should compensate for nonthermal velocities such as the ones reported here in order to extract instrumental widths that are free of nonthermal broadening.

Jeffrey W Brosius↗
NASA NTRS1973

Thermal and nonthermal X-ray bursts observed from OSO-7

The UCSD solar X-ray experiment on the OSO-7 observes X-rays in the 2 to 15 keV range with a proportional counter and in the 10.6 to 300 keV range with a scintillation counter. The dynamic range and instrument parameters are chosen to separate X-ray emission due to a hot thermal plasma from that due to nonthermal electron populations for a large number of X-ray events associated with small flares. Many different morphological classes have been observed in the 200 or so principal events observed between October 1971 and June 1972. For events which have both a thermal and nonthermal component, we can perform an analysis which shows that in not all events is it possible for the nonthermal electrons to energize the thermal plasma. We observe many events which have no nonthermal component, at least one event which was purely power law on initiation, and several events which had a long, slow decay of the hard X-rays.

Peterson, L. E.↗
NASA NTRS1993

Acceleration efficiency in nonthermal sources and the soft gamma rays from NGC 4151 observed by OSSE and SIGMA

We show that the recent observations of the Seyfert galaxy NGC 4151 in hard X-rays and soft gamma rays by the OSSE and SIGMA detectors on board CGRO and GRANAT, respectively, are well explained by a nonthermal model with acceleration of relativistic electrons at an efficiency of less than 50 percent and with the remaining power dissipated thermally in the source (the standard nonthermal e(+/-) pair model assumed 100 percent efficiency). Such an acceleration efficiency is generally expected on physical grounds. The resulting model unifies previously proposed purely thermal and purely nonthermal models. The pure nonthermal model for NGC 4151 appears to be ruled out. The pure thermal model gives a worse fit to the data than our hybrid nonthermal/thermal model.

Zdziarski, Andrzej A.↗
NASA NTRS1994

Nonthermal processes in flaring X-ray-bright points

X-ray-bright point (XBPs) are known to show variability on a number of timescales, including impulsive X-ray brightenings. The relationship between these XBP 'flares' and normal solar flares is poorly known. A fundamental question is whether nonthermal acceleration of particles takes place in XBP flares. We address this issue by searching for nonthermal radio emission at metric wavelengths from flaring XBPs identified in Yohkoh soft x-ray telescope (SXT) data. Unequivocal evidence for type III-like radio bursts, usually attributed to beams of nonthermal electrons on open field lines, is found. This suggests that XBP flares are similar to normal flares and can indeed accelerate nonthermal populations of energetic particles.

Kundu, M. R.↗
NASA NTRS1999

A Study of Nonthermal X-Ray and Radio Emission from the O Star 9 Sgr

The observed X-ray and highly variable nonthermal radio emission from OB stars has eluded explanation for more than 18 years. The most favorable model of X-ray production in these stars (shocks) predicts both nonthermal radio and X-ray emission. The nonthermal X-ray emission should occur above 2 keV and the variability of this X-ray component should also be comparable to the observed radio variability. To test this scenario, we proposed an ASC/VLA monitoring program to observe the OB star, 9 Sgr, a well known nonthermal, variable radio source and a strong X-ray source. We requested 625 ks ASCA observations with a temporal spacing of approximately 4 days which corresponds to the time required for a density disturbance to propagate to the 6 cm radio free-free photosphere. The X-ray observations were coordinated with 5 multi-wavelength VLA observations. These observations represent the first systematic attempt to investigate the relationship between the X-ray and radio emission in OB stars.

Waldron, Wayne L.↗
NASA NTRS2002

Observation of Nonthermal Emission from the Supernova Remnant IC443 with RXTE

In this paper we present analysis of X-ray spectra from the supernova remnant IC443 obtained using the PCA on RXTE. The spectra in the 3 - 20 keV band are well fit by a two-component model consisting of thermal and nonthermal components. We compare these results with recent results of other X-ray missions and discuss the need for a cut-off in the nonthermal spectrum. Recent Chandra and XMM-Newton observations suggest that much of the nonthermal emission from IC443 can be attributed to a pulsar wind nebula. We present the results of our search for periodic emission in the RXTE PCA data. We then discuss the origin o f the nonthermal component and its possible association with the unidentified EGRET source.

Sturner, S. J.↗
NASA NTRS2007

Nonthermal X-ray Spectral Flattening toward Low Energies in Early Impulsive Flares

The determination of the low-energy cutoff to nonthermal electron distributions is critical to the calculation of the nonthermal energy in solar flares. The most direct evidence for low-energy cutoffs is flattening of the power-law, nontherma1 X-ray spectra at low energies. However, because of the plasma preheating often seen in flares, the thermal emissions at low energies may hide such spectral flattening of the nonthermal component. We select a category of flares, which we call "early impulsive flares", in which the > 25 keV hard X-ray (HXR) flux increase is delayed by less than 30 s after the flux increase at lower energies. Thus, the plasma preheating in these flares is minimal, so the nonthermal spectrum can be determined to lower energies than in flares with significant preheating. Out of a sample of 33 early impulsive flares observed by the Ramaty High Energy Solar Spectroscopy Imager (RHESSI), 9 showed spectral flattening toward low energies. In these events, the break energy of the double power-law fit to the HXR spectra lies in the range of 10-50 keV, significantly lower than the value we have seen for other flares that do not show such early impulsive emissions. In particular, it correlates with the HXR flux. After correcting the spatially-integrated spectra for albedo from isotropically emitted X-rays and using RHESSI imaging spectroscopy to exclude the extended albedo halo, we find that albedo associated with isotropic or nearly isotropic electrons can only account for the spectral flattening in 3 flares near Sun center. The spectral flattening in the remaining 6 flares is found to be consistent with the existence of a low-energy cutoff in the electron spectrum, falling in the range of 15-50 keV, which also correlates with the HXR flux.

Holman, Gordon D.↗
DOE OSTI2021

Nanoparticle dynamics in the spatial afterglows of nonthermal plasma synthesis reactors

Nonthermal plasma flow tube reactors are industrially scalable systems for the production of nanocrystal (NC) based materials and coatings. One key advantage of nonthermal plasma synthesis is the ability to both synthesize NCs and deposit films in a single reactor, as at the reactor outlet, NCs can be inertially deposited onto a target substrate. The size and morphology of deposited particles can substantially influence the film structure and function. Though NCs are typically near-spherical and monodispersed as-produced in plasma synthesis reactors, NC charge and growth dynamics can be altered substantially when NCs are sampled out of the plasma and through the spatial afterglow region, affecting deposition. Experiments have demonstrated changes of NC size and charge in the spatial afterglow; however, these dynamics remain unexplored and unexplained via theory and simulation. To address this, we developed a constant number Monte Carlo (CNMC) simulation model to examine the mechanisms of NC decharging and growth in the spatial afterglow of plasma flow tube reactors. Collisions between NC and plasma species, diffusive deposition, and electron desorption from NCs are incorporated in the CNMC simulation. The simulation results are specifically compared with previous experiments on Si NCs synthesized from a low pressure Ar-SiH 4 nonthermal plasma reactor. Furthermore, the experiment-model comparison shows that CNMC models can be implemented which accurately model NC size distribution evolution in a spatial afterglow. Simultaneously, results show that improved collision models, energetic species diffusion models, and electron desorption models will be necessary to accurately depict NC dynamics in spatial afterglows.

42 ENGINEERING↗
DOE OSTI2023

Plasma-Catalyst Synergy in the One-Pot Nonthermal Plasma-Assisted Synthesis of Aromatics from Methane

Electrification of the methane dehydroaromatization reaction with the use of nonthermal plasmas could alleviate the high-temperature requirement for this process while promoting the formation of valuable aromatics. Here, in this work, we evaluate the use of nonthermal plasma to investigate methane activation and conversion to aromatics by systematically varying bulk gas temperature in a one-pot, plasma-stimulated catalytic reactor over Mo/H-ZSM-5 and metal-free H-ZSM-5 catalysts. We report that Mo is not required for methane activation under low-temperature plasma conditions (573–773 K), and methane conversions up to ~15% with a 1:1 methane/N 2 feed are obtained under a 10 W plasma. However, Mo contributes to the formation of aromatics in the presence of a plasma at 773 K, achieving close to a 2-fold increase in the production of aromatics when compared to unmodified H-ZSM-5. Further, the exposure of as-prepared Mo/H-ZSM-5 to the methane plasma feed induces the formation of Mo-carbide phases in the temperature range studied. These findings highlight the complex roles of nonthermal plasmas in the direct activation of methane and the importance of plasma-catalyst design to facilitate aromatization reactions under plasma-assisted reaction conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

New Insights into Nonthermal Plasma-Assisted Poly(vinyl alcohol) Depolymerization Catalyzed by TiO 2

Here, in this study, we investigated the solid residual poly(vinyl alcohol) (PVA) and TiO 2 after nonthermal air, CO 2 , and N 2 plasma depolymerization in the absence and presence of TiO 2 . Scanning electron microscopy studies showed the absence of highly viscous tar and carbonaceous residues on the surfaces of PVA and TiO 2 . In the absence of TiO 2 , PVA particles exhibited micron-sized holes on their surfaces, whereas in the presence of TiO 2 , the surface roughness of PVA particles was observed at the submicron scale. These observations suggest that TiO 2 facilitates the even distribution of nonthermal plasma at a submicron scale, leading to a more uniform depolymerization of PVA surfaces. Raman, Fourier transform infrared spectroscopy, and X-ray absorption spectroscopy showed that (i) the surface of residual PVA contains mainly ketone functional groups and less C-H bonds than the pristine PVA and (ii) further confirmed the absence of highly viscous tar and carbonaceous residues on both used TiO 2 and residual PVA. The nuclear magnetic resonance and mass spectroscopy suggested that the PVA is growing back to poly polyvinyl acetate by the esterification reaction, and the ethers are produced by the acetal reaction between PVA and aldehyde. The transmission electron microscopy and X-ray diffraction analysis indicated no major crystal structural change of the TiO 2 catalyst after the plasma reactions. This study demonstrates that nonthermal plasma-assisted depolymerization is a viable alternative to thermal depolymerization, offering the unique advantage of converting polymer wastes into gaseous small organic molecules without generating recalcitrant viscous tar and carbonaceous residues on the surfaces of the polymer and TiO 2 catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Lower hybrid drift instability in nonthermal plasmas

Lower hybrid drift instability (LHDI) is driven by the cross-field current and operates in the vicinity of the lower-hybrid frequency, between the ion- and electron-gyro frequencies, and with wavelengths between the electron and ion thermal gyro radii. The free energy source that drives this instability resides in the density gradient associated with an inhomogeneous plasma. The existing literature on LHDI assumes that the charged particle distribution function is given by a Maxwellian form, but the space plasma is pervasively observed to feature nonthermal characteristics. This paper extends the theory of LHDI to nonthermal plasmas. The generalized theory of LHDI is, thus, applicable to various space plasma environments characterized by nonthermal plasma velocity distribution functions.

Arya, Neetasha (ORCID:0009000236075605)↗