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All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

X-ray variability and period determinations in the eclipsing polar DP Leonis

We present an analysis of our ROSAT position sensitive proportional counter (PSPC) observations on the eclipsing magnetic cataclysmic variable DP Leo. The soft X-ray spectrum is modeled by a blackbody of kT = 24.8(sup +2.6 sub -8.1) eV. Severe limits are placed upon the flux from any hard bremsstrahlung component. A strong soft X-ray excess, with respect to hard X-ray emission, is found. The soft X-ray blackbody luminosity is larger than both the cyclotron and bremsstrahlung luminosities. An upper limit of 500 pc is obtained for the system's distance based upon the X-ray absorption (N(sub H) less than 5 x 10(exp 19)/sq cm) and an estimate of 260(sup +150 sub -100) pc is determined from a published measurement of the secondary's flux. For the derived blackbody fit, the bolometric luminosity is found to be L(sub bb, bol) = 1.4(sup +7.1 sub -0.3) x 10(exp 31)(d/260 pc)(exp 2) ergs/s. Absorption by the accretion stream produces an intensity dip prior to each eclipse. Extreme variability in the shape of the light curve from eclipse to eclipse demonstrates that changes in the rate of accretion onto the white dwarf, the sizes of accretion filaments, or variations in the location or amount of absorbing matter in the system occur on timescales shorter than the orbital period (89.8 minutes). No evidence exists for accretion onto the stronger (59 MG) magnetic pole in the ROSAT data. A new ephemeris is presented for the eclipse of the white dwarf emission region by the secondary star and another is produced for the orbital conjunction of the two components. The rotation of the white dwarf is shown to be faster than the orbital period by (5.3 +/- 1.1) x 10(exp -3) s. The origin of the asynchronous rotation may be activity cycle included orbital period variations or oscillations of the white dwarf's main pole about an equilibirium position. The accretion stream is modeled assuming that disruption of the stream along magnetic field lines occurs close to the white dwarf. The ROSAT intensity dip is explained using this model and the results are shown to be consistent with contemporaneous optical observations.

Robinson, Craig R.↗
NASA NTRS1996

Plasma Properties and Magnetic Field Structure of the Solar Corona, Based on Coordinated Max 1991 Observations from SERTS, the VLA, and Magnetographs

The purposes of this investigation are to determine the plasma properties and magnetic field structure of the solar corona using coordinated observations obtained with NASA/GSFC's Solar EUV Rocket Telescope and Spectrograph (SERTS), the Very Large Array (VLA), and magnetographs. The observations were obtained under the auspices of NASA's Max '91 program. The methods of achieving the stated purposes are to use SERTS spectra and spectroheliograms to determine coronal plasma properties such as temperature, density, and emission measure. These properties are subsequently used to calculate the intensity of the thermal bremsstrahlung microwave emission from the coronal plasma (the minimum microwave intensity expected from the emitting plasma). This, in turn, can be used to establish which emission mechanism(s) contribute to the observed microwave emission. Because both mechanisms that may contribute to quiescent active region microwave emission (thermal bremsstrahlung and thermal gyroemission) depend upon the coronal magnetic field in known ways, this information can ultimately be used to derive the coronal magnetic field. Ideally, three-dimensional models of the coronal plasma and magnetic field which are consistent with all of the EUV spectra and spectroheliograms, as well as with the intensity and polarization maps at all of the microwave observing frequencies, can be derived. For completeness, the coronal magnetic field derived from the coordinated multiwaveband observations must be compared with extrapolations from photospheric magnetograms.

Brosius, Jeffrey W.↗
NASA NTRS2002

RHESSI Investigations of the Neupert Effect in Solar Flares

In many solar flares the time integral of the hard X-ray emission closely matches the temporal variation of the soft X-ray emission. This is known as the Neupert Effect and is believed to result when the same accelerated electrons that produce the bremsstrahlung hard X-rays also heat the plasma that produces the thermal bremsstrahlung soft X-rays. The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is uniquely capable of investigating this effect since is covers the soft (down to 3 keV) and hard X-ray energy ranges with keV energy resolution, arcsecond-class angular resolution, and sub-second time resolution. Several GOES M-class flares have already been detected that show this general effect, but the detailed time histories suggest that there must be other heating mechanisms besides the thermalization of accelerated electrons that are heating the soft X-ray emitting plasma, even during the impulsive phase. Spatially-resolved hard and soft X-ray observations of these flares are also being investigated to determine what fraction of the heating is produced by the accelerated electrons.

Dennis, Brian R.↗
NASA NTRS2004

Energetic Electrons in Solar Flares - As Viewed in X-Rays

Hard X-ray observations provide the most direct diagnostic we have of the suprathermal electrons and the hottest thermal plasma present in solar flares. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is obtaining the most comprehensive observations of individual solar flares ever available in hard X-rays. For the first time, high-resolution spectra are available for a large number of flares that accurately display the spectral shape and its evolution and, in many cases, allow us to identify the transition from the bremsstrahlung X-rays produced by suprathermal electrons to the bremsstrahlung at lower energies emitted by thermal plasma. Also, for the first time, images can be produced in arbitrary energy bands above 3 keV, and spectra of distinct imaged components can be obtained. I will review what we have learned from RHESSI observations about flare suprathermal electron distributions and their evolution Next, I will present computations of the energy deposited by these suprathermal electrons in individual flares and compare this with the energy contained in the hot thermal plasma. I will point out unsolved problems in deducing both suprathermal electron distributions and the energy content of the thermal plasma, and discuss possible solutions. Finally, I will present evidence that electron acceleration is associated with magnetic reconnection in the corona.

Holman, Gordon D.↗
NASA NTRS2010

Intense Gamma-Ray Flashes Above Thunderstorms on the Earth and Other Planets

Intense millisecond flashes of MeV photons have been observed with space-borne detectors in Earth orbit. They are expected to be present on other planets that exhibit lightning. The terrestrial gamma-ray flashes (TGFs) were discovered with the Burst and Transient Source Experiment (BATSE) aboard the Compton Gamma-Ray Observatory (CGRO) in the early 1990s. They are now being observed with several other instruments, including the Gamma-ray Burst Monitor (GBM) detectors on the Fermi Gamma-ray Space Telescope. Although Fermi- GBM was designed and optimized for the observation of cosmic gamma-ray bursts (GRBs), it has unprecedented capabilities for TGF observations. The TGFs usually have extremely hard continuous spectra, typical of highly- Comptonized bremsstrahlung radiation. These spectral are harder than those of GRBs, with photons extending to over 40 MeV. The most likely origin of these high-energy photons is bremsstrahlung radiation produced by a relativistic "runaway avalanche" electron beam. Such a beam is expected to be produced in an extended, intense electric field in or above thunderstorm regions. The altitude of origin and beaming characteristics of the radiation are quite uncertain. They have generated considerable observational and theoretical interest in recent years. This talk will give an overview of the all of the space-borne observations of TGFs that have been made thus far. Instruments are being designed specifically for TGF observations from new spacecraft as well as from airborne platforms

Fishman, Gerald J.↗
NASA NTRS2010

Space-Borne Observations of Intense Gamma-Ray Flashes (TGFs) Above Thunderstorms

Intense millisecond flashes of MeV photons are being observed with space-borne detectors. These terrestrial gamma-ray flashes (TGFs) were discovered with the Burst and Transient Source Experiment (BATSE) aboard the Compton Gamma-Ray Observatory (CGRO) in the early 1990s. They are now being observed with several other instruments, including the Gamma-ray Burst Monitor (GBM) detectors on the Fermi Gamma-ray Space Telescope. Although Fermi-GBM was designed and optimized for the observation of cosmic gamma-ray bursts (GRBs), it has unprecedented capabilities for TGF observations. The TGFs usually have extremely hard continuous spectra, typical of highly-Comptonized bremsstrahlung radiation. These spectral are harder than those of GRBs, with photons extending to over 40 MeV. The most likely origin of these high-energy photons is bremsstrahlung radiation produced by a relativistic runaway avalanche electron beam. Such a beam is expected to be produced in an extended, intense electric field in or above thunderstorm regions. The altitude of origin and beaming characteristics of the radiation are quite uncertain. These TGFs may produce an appreciable radiation dose to passengers and crew in nearby aircraft. They have generated considerable observational and theoretical interest in recent years. Instruments are being designed specifically for TGF observations from new spacecraft as well as from airborne platforms.

Fishman, Gerald J.↗
NASA NTRS2011

A Multiwavelength Study of Cygnus X-1: The First Mid-Infrared Spectroscopic Detection of Compact Jets

We report on a Spitzer/IRS (mid-infrared), RXTE /PCA+HEXTE (X-ray), and Ryle (radio) simultaneous multi-wavelength study of the micro quasar Cygnus X-I, which aimed at an investigation of the origin of its mid-infrared emission. Compact jets were present in two out of three observations, and we show that they strongly contribute to the mid-infrared continuum. During the first observation, we detect the spectral break - where the transition from the optically thick to the optically thin regime takes place - at about 2.9 x 10(exp 13) Hz. We then show that the jet's optically thin synchrotron emission accounts for the Cygnus X-1's emission beyond 400 keY, although it cannot alone explain its 3-200 keV continuum. A compact jet was also present during the second observation, but we do not detect the break, since it has likely shifted to higher frequencies. In contrast, the compact jet was absent during the last observation, and we show that the 5-30 micron mid-infrared continuum of Cygnus X-I stems from the blue supergiant companion star HD 226868. Indeed, the emission can then be understood as the combination of the photospheric Raleigh-Jeans tail and the bremsstrahlung from the expanding stellar wind. Moreover, the stellar wind is found to be clumpy, with a filling factor f(sub infinity) approx.= 0.09-0.10. Its bremsstrahlung emission is likely anti-correlated to the soft X-ray emission, suggesting an anticorrelation between the mass-loss and mass-accretion rates. Nevertheless, we do not detect any mid-infrared spectroscopic evidence of interaction between the jets and the Cygnus X-1's environment and/or companion star's stellar wind.

Rahoui, Farid↗
NASA NTRS2014

NuSTAR J163433-4738.7: A Fast X-Ray Transient in the Galactic Plane

During hard X-ray observations of the Norma spiral arm region by the Nuclear Spectroscopic Telescope Array (NuSTAR) in 2013 February, a new transient source, NuSTAR J163433-4738.7, was detected at a significance level of 8sigma in the 3-10 keV bandpass. The source is consistent with having a constant NuSTAR count rate over a period of 40 ks and is also detected simultaneously by Swift at lower significance. The source is not significantly detected by NuSTAR, Swift, or Chandra in the days before or weeks after the discovery of the transient, indicating that the strong X-ray activity lasted between approx. 0.5 and 1.5 days. Near-infrared imaging observations were carried out before and after the X-ray activity, but we are not able to identify the counterpart. The combined NuSTAR and Swift energy spectrum is consistent with a power law with a photon index of Gamma = 4.1(+1.5/−1.0) (90% confidence errors), a blackbody with kT = 1.2+/-0.3 keV, or a Bremsstrahlung model with kT = 3.0(+2.1/−1.2) keV. The reduced-χ2 values for the three models are not significantly different, ranging from 1.23 to 1.44 for 8 degrees of freedom. The spectrum is strongly absorbed with NH = (2.8(+2.3/−1.4) × 10(exp23) cm(exp−2), (9(+15 /−7) ) × 10(exp22) cm(exp−2), and (1.7(+1.7/−0.9)) × 10(exp23) cm(exp−2), for the power-law, blackbody, and Bremsstrahlung models, respectively. Although the high column density could be due to material local to the source, it is consistent with absorption from interstellar material along the line of sight at a distance of 11 kpc, which would indicate an X-ray luminosity greater than 10(exp34) erg s(exp−1). Although we do not reach a definitive determination of the nature of NuSTAR J163433-4738.7, we suggest that it may be an unusually bright active binary or a magnetar.

Near-infrared imaging observations↗
NASA NTRS2018

Gamma Energy Evaluation for Creation of Cd-111(sub m), In-113(sub m), and In-115(sub m) Isotopes

NASA Glenn Research Center is investigating nuclear reactions in deuterated materials exposed to bremsstrahlung photons with kinetic energies from 1-3MeV. Recent experiments used a continuous beam Dynamitron electron accelerator with a braking target. Electron beam energy loss verication was desired and experiments using cadmium and indium were completed which are known to transition to excited metastable states after exposure to bremsstrahlung photons. The gamma spin-up of Cd-111, In-113, and In-115 are with photon beam energies of 1017keV, 1024keV, and 941keV respectively. Recent tests corroborated published gamma energies using a beam energy loss of 62 to 74keV.

Benyo, Theresa L.↗
DOE OSTI2024

Searching for Strongly-Interacting Dark Matter with the Heavy Photon Search Experiment

The Heavy Photon Search Experiment (HPS) is a fixed-target experiment at Jefferson Lab’s Hall B, designed to explore a hidden sector (HS) of particles containing dark matter and a new force mediator known as the “heavy photon” (A'). The A' is a massive spin-1 gauge boson associated with a new U (1)D symmetry in the HS that kinetically mixes with the Standard Model () photon with a weak coupling strength parameterized by ¿, with ¿2 ~ 10-2 -10-10. HPS utilizes a high-intensity electron beam on a thin tungsten target to produce heavy photons in the MeV-GeV mass range via “dark bremsstrahlung,” a process analogous to SM bremsstrahlung but suppressed by ¿2. The A' can decay resonantly to SM leptons, allowing HPS to conduct both mass resonance searches for prompt decays (large ¿) and displaced vertex searches for long-lived particles (small ¿). In addition to the minimal A' model, HPS probes more complex extensions such as the QCD-like strongly-interacting massive particles (SIMPs) HS containing “dark” pions (pD) and vector mesons (VD), with pD as dark matter candidates. These particles introduce new thermal dark matter freeze- out scenarios and visible signals through long-lived VD decays to SM leptons, which are accessible to HPS. This analysis conducted a displaced vertex search for VD ¿ e-e+ in the mass range 30 MeV to 124 MeV and ¿ between 10-6 < ¿ < 10-2 using data from the 2016 Engineering Run (10.753 nb-1) at 2.3 GeV. Unlike the minimal A' search, SIMP signal kinematics required new approaches to signal normalization and SM background rejection. The strongest signal evidence was a local p-value of 0.01317 for mVD = 119 MeV, corresponding to a global significance of 0.9s. Although no signal was found, this search excluded a region of the SIMP parameter space at 90 % confidence. This work demonstrates HPS’s competitive capability to probe SIMP sectors within cosmologically significant parameters and introduces a new method for HPS displaced vertex searches using track vertical impact parameter cuts

Spellman, Alic [Univ. of California, Santa Cruz, C↗
DOE OSTI2021

High purity 47 Sc production using high-energy photons and natural vanadium targets

We report Scandium-47 ( 47 Sc) is of high value for targeted radiotherapy and theranostics; we report a novel, cost-effective approach to produce extremely high-purity 47 Sc via photonuclear irradiation of natural vanadium. Irradiations at bremsstrahlung end-point energies below 26 and at 38 MeV produce > 99.99% and 98.8 ± 3.1% pure 47 Sc (respectively). Linear scaling of experimental data suggests producing 100+ mCi quantities of 47 Sc may be feasible via this approach. Future research into refinement and scale-up to support pre-clinical and clinical research with this production pathway is recommended.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2022

Enhancement of high energy X-ray radiography using compound parabolic concentrator targets

We report an increase in MeV energy bremsstrahlung x-ray production using compound parabolic concentrators (CPC) compared to flat solid targets during relativistic laser-plasma experiments on a 140 J, 150 fs laser system using an f/40 focusing optic. CPC enhanced targets show a > 3x increase in high energy x-ray production over planar foil targets. Furthermore, this enhancement in x-ray energy spectra shows a direct improvement in the radiography of an image quality indicator (IQI) object with a 20 g/cm 2 areal density.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Characterization of an RF-driven argon plasma at atmospheric pressure using broadband absorption and optical emission spectroscopy

Atmospheric pressure plasmas in argon are of particular interest due to the production of highly excited and reactive species enabling numerous plasma-aided applications. In this contribution, we report on absolute optical emission and absorption spectroscopy of a radio frequency (RF) driven capacitively coupled argon glow discharge operated in a parallel-plate configuration. This enabled the study of all key parameters including electron density and temperature, gas temperature, and absolute densities of atoms in highly electronically excited states. The space and time-averaged electron density and temperature were determined from the measurement of the absolute intensity of the electron-atom bremsstrahlung in the visible range. Considering the non-Maxwellian electron energy distribution function, an electron temperature (T e ) of 2.1 eV and an electron density (n e ) of 1.1 × 10 19 m –3 were obtained. The time-averaged and spatially resolved absolute densities of atoms in the metastable (1s 5 and 1s 3 ) and resonant (1s 4 and 1s 2 ) states of argon in pure Ar and Ar/He mixture were obtained by broadband absorption spectroscopy. The 1s 5 metastable atoms had the largest density near the sheath region with a maximum value of 8 × 10 17 m –3 , while all other 1s states had densities of at most 2 × 10 17 m –3 . Here, the dominant production and loss mechanisms of these atoms were discussed, in particular, the role of radiation trapping. We conclude with a comparison of the plasma properties of the argon RF glow discharges with the more common He equivalent and highlight their differences.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

A dual high-energy radiography platform with 15 μ m resolution at the National Ignition Facility

To study matter at extreme densities and pressures, we need mega laser facilities such as the National Ignition Facility as well as creative methods to make observations during timescales of a billionth of a second. To facilitate this, we developed a platform and diagnostic to characterize a new point-projection radiography configuration using two micro-wires irradiated by a short pulse laser system that provides a large field of view with up to 3.6 ns separation between images. In this work, we used tungsten-carbide solid spheres as reference objects and inferred characteristics of the back-lighter source using a forward-fitting algorithm. The resolution of the system is inferred to be 15 μm (using 12.5 μm diameter wires). The bremsstrahlung temperature of the source is 70–300 keV, depending on laser energy and coupling efficiency. By adding the images recorded on multiple stacked image plates, the signal-to-noise of the system is nearly doubled. The imaging characterization technique described here can be adapted to most point-projection platforms where the resolution, spectral contrast, and signal-to-noise are important.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Non-equilibrium plasma generation via nano-second multi-mode laser pulses

The formation and growth of plasma kernels generated via nano-second mode-beating laser pulses is investigated here via a non-equilibrium self-consistent computational model. Chemically reactive Navier–Stokes equations are used to describe the hydrodynamics, and non-equilibrium effects are taken into account with a two-temperature model. Inverse Bremsstrahlung and multiphoton ionization are included self-consistently in the model via a coupled solution of the plasma governing equations and the radiative transfer equation (that describes the laser beam propagation and attenuation). A self-consistent approach (despite carrying additional challenges) minimizes the empiricism and it allows for a more accurate description since it prevents both the utilization of artificial plasma seeds to trigger the breakdown and the implementation of tuning parameters to simulate the laser-energy deposition. The advantages of this approach are confirmed by the good agreement between the numerically predicted and the experimentally measured plasma boundary evolution and absorbed energy. This also holds true for the periodic plasma kernel structures that, as suggested by the experiments and confirmed by the simulations presented here, are connected to the modulating frequency.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Demonstration of plasma mirror capability for the OMEGA Extended Performance laser system

A plasma mirror platform was developed for the OMEGA-EP facility to redirect beams, thus enabling more flexible experimental configurations as well as a platform that can be used in the future to improve laser contrast. The plasma mirror reflected a short pulse focusing beam at 22.5° angle of incidence onto a 12.5 μm thick Cu foil, generating Bremsstrahlung and k α x rays, and accelerating ions and relativistic electrons. By measuring these secondary sources, the plasma mirror key performance metrics of integrated reflectivity and optical quality are inferred. It is shown that for a 5 ± 2 ps, 310 J laser pulse, the plasma mirror integrated reflectivity was 62 ± 13% at an operating fluence of 1670 J cm –2 , and that the resultant short pulse driven particle acceleration and x-ray generation indicate that the on target intensity was 3.1 × 10 18 W cm –2 , which is indicative of a good post-plasma mirror interaction beam optical quality. By deriving the plasma mirror performance metrics from the secondary source scalings, it was simultaneously demonstrated that the plasma mirror is ready for adoption in short pulse particle acceleration and high energy photon generation experiments using the OMEGA-EP system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Predicted performance of a tangential viewing hard x-ray camera for the DIII-D high field side lower hybrid current drive experiment

High field side launch of lower hybrid current drive (LHCD) has improved accessibility and penetration over low field side launch on DIII-D. Simulations predict single pass absorption under a wide range of plasma conditions. Hard x-ray (HXR) measurement of LHCD generated fast electron bremsstrahlung (50–250 keV) will validate wave propagation and absorption. Emissivity profiles are recovered from one-dimensional inversion of HXR brightness to determine LH damping location, fast electron slowing down time, and some indication of the fast electron energy. The camera will be implemented by populating 32 tangential sightlines of the existing Gamma Ray Imager with Kromek SPEARTM Cadmium Zinc Telluride (CZT) detectors sensitive to 10–1000 keV photons with 10 keV energy resolution. Expected count rates allow for <0.5 ms time resolution. Pulses are processed using 50 ns shaping time Cremat CR-200 Gaussian shaping modules and are digitized by 25 MHz D-TACQ ACQ216 digitizers. The performance of the HXR camera is evaluated by comparing predicted fast electron density profiles and inverted synthetic brightnesses obtained from the ray-tracing/Fokker–Planck codes GENRAY/CQL3D. Inversions closely matched predicted fast electron profiles for a range of experimental parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Ultra-compact x-ray spectrometer for high-repetition-rate laser–plasma experiments

Here, we present in this work the development of an ultra-compact, multi-channel x-ray spectrometer (UCXS). This diagnostic has been specially built and adapted to perform at high-repetition-rate (>1 Hz) for high-intensity, short-pulse laser plasma experiments. X-ray filters of varying materials and thicknesses are chosen to provide spectral resolution up to ΔE ≈ 1 keV over the x-ray energy range of 1–30 keV. These filters are distributed over a total of 25 channels, where each x-ray filter is coupled to a single scintillator. The UCXS is designed to detect and resolve a large variety of laser-driven x-ray sources such as low energy bremsstrahlung emission, fluorescence, and betatron radiation (up to 30 keV). Preliminary results from commissioning experiments at the ABL laser facility at Colorado State University are provided.

47 OTHER INSTRUMENTATION↗