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NASA NTRS1985

Electrostatic wave propagation and trapping near the magnetic equator

Results of a two-dimensional ray tracing computer code, based on Snell's law, for electrostatic wave propagation in a dipole magnetic field are discussed. A survey of possible ray paths varying a wide range of parameters is conducted for low-harmonic Bernstein modes in a high-density plasma. It is shown that the ray paths exhibit similarity with radial distance and that there exists the possibility of two classes of wave statistics of the equator: a broad emission region extending to about + or - 4 deg and a class of events restricted to the smaller region of 1-2 deg about the magnetic equator. The regulating parameter between these two types of events is the transition energy from the isotropic background electrons to the unstable distribution of superthermals. Ray paths for propagation in the magnetic equatorial plane are considered and an explanation is given for ray focusing in the equatorial plane based on electron gyroradius considerations.

Barbosa, D. D.↗

NASA NTRS1998

Angular Broadening: Effects of Nonzero, Spatially Varying Plasma Frequency Between the Source and Observer

Angular broadening of radiation due to scattering by density irregularities is usually described using geometric optics (GO) or the parabolic wave equation (PWE) with the assumptions that the radiation frequency f greatly exceeds the local plasma frequency f(sub p0) or that f(sub p0)/f is constant along the path. These assumptions are inappropriate for many solar system radio phenomena. Here the PWE and GO formalisms are extended to treat angular broadening in plasmas with nonzero, spatially varying ratios, f(sub p0)(z)/f < 1. The new PWE results show that the correlation function, scattered angular spectrum, and other quantities are modified by inclusion of a denominator factor [1 - f(sup 2, sub p0)(z prime)/f prime] inside the path integral over z prime, while the mean-square scattering angle depends on both f(sub p0)(z)/f at the observer and the foregoing factor inside the path integral. The PWE and GO predictions for are identical and involve equivalent assumptions. Previous GO and PWE results are recovered in the limits that f(sub p0)(z prime)/f is constant or zero. The new PWE and GO results will permit more accurate calculation of angular broadening for solar system and astrophysical sources. Moreover and importantly, due to the PWE and GO results for being identical, previous GO analyses of in solar system contexts are essentially correct, except for the neglect of or minor deficiencies in the treatment of nonzero, spatially varying f(sub p0)/f effects. The identical GO and PWE results for and the form of the PWE equation for the correlation function raise questions as to whether diffraction is unimportant for angular broadening (under the usual PWE conditions). Future direct comparisons of the PWE predictions with angular spectra calculated using existing GO ray-tracing codes should answer these questions. Diffraction effects are probably important when the medium and turbulence are not sufficiently homogeneous transverse to the central ray path. The implications are also discussed for studies of the 2-3.5 kHz radiation observed in the outer heliosphere.

Cairns, Iver H.↗

NASA NTRS1991

Computing Performance Of An Optical System

Collection of programs performs complicated ray-tracing and diffraction calculations. Optical Surface Analysis Code (OSAC) designed to provide comprehensive analysis of performance of optical system. Analyzes both conventional and x-ray systems. Composed of nine compatible programs executed in a sequence defined by user. Written in FORTRAN IV.

Glenn, P.↗

NASA NTRS1982

Grazing incidence relay optics

The necessity to work in the focal plane of the primary mirrors has been one of the factors limiting the utility of grazing incidence telescopes in X-ray astronomy. In connection with the reported investigation, computer ray tracing programs have been used to study the performance of several grazing incidence relay optics (GIRO) systems used together with a large nested solar X-ray telescope. It was found that GIRO magnifiers are useful to map appropriate sized regions of the sun onto available CCD detectors. GIRO collimators can be used together with an X-ray spectrometer to study the X-ray spectrum from very small regions on the sun. Attention is given to the stationary mode, the tracking mode, and the size of GIRO elements. It is found that for a given GIRO size and magnification a use of the diverging system has the advantage of reducing the overall length of the main telescope-GIRO combination. However, the resolution provided by the diverging GIRO may not be as good as that obtained with the corresponding converging GIRO.

Chase, R. C.↗

NASA NTRS1992

Surface finish quality of the outer AXAF mirror pair based on x ray measurements of the VETA-I

We employ the X-ray measurements of the VETA-I taken at the X-Ray Calibration Facility (XRCF) of the Marshall Space Flight Center (MSFC) to extract information about the surface finish quality of the outermost pair of AXAF mirrors. The particular measurements we consider are one dimensional scans of the core of the point response function (PRF) (full width half maximum (FWHM) scans), the encircled energy as a function of radius, and one dimensional scans of the wings of the PRF. We discuss briefly our ray trace model which incorporates the numerous effects present in the VETA-I test, such as the finite source distance, the size and shape of the X-ray source, the residual gravitational distortions of the optic, the despace of the VETA-I, and particulate contamination. We show how the data constrain the amplitude of mirror surface deviations for spatial frequencies greater than about 0.1 mm(exp -1). Constraints on the average amplitude of circumferential slope errors are derived as well.

Hughes, John P.↗

NASA NTRS1998

Correlations Between the Cosmic X-Ray and Microwave Backgrounds: Constraints on a Cosmological Constant

In universes with significant curvature or cosmological constant, cosmic microwave background (CMB) anisotropies are created very recently via the Rees-Sciama or integrated Sachs-Wolfe effects. This causes the CMB anisotropies to become partially correlated with the local matter density (z less than 4). We examine the prospects of using the hard (2- 10 keV) X-ray background as a probe of the local density and the measured correlation between the HEAO1 A2 X-ray survey and the 4-year COBE-DMR map to obtain a constraint on the cosmological constant. The 95% confidence level upper limit on the cosmological constant is OMega(sub Lambda) less than or equal to 0.5, assuming that the observed fluctuations in the X-ray map result entirely from large scale structure. (This would also imply that the X-rays trace matter with a bias factor of b(sub x) approx. = 5.6 Omega(sub m, sup 0.53)). This bound is weakened considerably if a large portion of the X-ray fluctuations arise from Poisson noise from unresolved sources. For example, if one assumes that the X-ray bias is b(sub x) = 2, then the 95% confidence level upper limit is weaker, Omega(sub Lambda) less than or equal to 0.7. More stringent limits should be attainable with data from the next generation of CMB and X-ray background maps.

Boughn, S. P.↗

NASA NTRS1992

Magnetospherically reflected whistlers as a source of plasmaspheric hiss

Ray-tracing simulations and estimates of whistler wave damping show that magnetospherically reflected whistlers can persist for about 100 s in a LF band (about 1 kHz). The combined contribution from whistler rays produced by a single lightning flash but entering the magnetosphere at different points form a continuous hisslike signal, as observed at a fixed point. Estimates indicate that the total whistler wave energy input into the magnetosphere from lightning discharges may maintain experimentally observed levels of magnetospheric hiss.

Draganov, A. B.↗

NASA NTRS2011

Mathematical Design Optimization of Wide-Field X-ray Telescopes: Mirror Nodal Positions and Detector Tilts

We describe a mathematical formalism for determining the mirror shell nodal positions and detector tilts that optimize the spatial resolution averaged over a field-of-view for a nested x-ray telescope, assuming known mirror segment surface prescriptions and known detector focal surface. The results are expressed in terms of ensemble averages over variable combinations of the ray positions and wave vectors in the flat focal plane intersecting the optical axis at the nominal on-axis focus, which can be determined by Monte-Carlo ray traces of the individual mirror shells. This work is part of our continuing efforts to provide analytical tools to aid in the design process for wide-field survey x-ray astronomy missions.

Elsner, R. F.↗

NASA NTRS2011

Mathematical Design Optimization of Wide-Field X-ray Telescopes: Mirror Nodal Positions and Detector Tilts

We describe a mathematical formalism for determining the mirror shell nodal positions and detector tilts that optimize the spatial resolution averaged over a field-of-view for a nested x-ray telescope, assuming known mirror segment surface prescriptions and known detector focal surface. The results are expressed in terms of ensemble averages over variable combinations of the ray positions and wavevectors in the flat focal plane intersecting the optical axis at the nominal on-axis focus, which can be determined by Monte-Carlo ray traces of the individual mirror shells. This work is part of our continuing efforts to provide analytical tools to aid in the design process for wide-field survey x-ray astronomy missions.

Elsner, Ronald↗

NASA NTRS2012

The Suppression of Star Formation by Powerful Active Galactic Nuclei

The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight corre1ation between the mass of the black hole and the mas. of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming ga1axies are usually dust-obscured and are brightest at infrared and submillimeter wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(exp 44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expe11ing the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

Dwek, E.↗

NASA NTRS1983

Optical surface analysis code (OSAC)

A computer program for the evaluation of surface ripple effects on an optical system is discussed. The program consists of a modification of conventional ray tracing so that the effects of all roughness frequency scales on image quality can be analyzed. The code is designed to deal with image quality problems arising in connection with X-ray telescopes and near-normal incidence systems used in the infrared, visible, and near-UV parts of the spectrum. The emphasis of the program analysis is on narrow angle scattering and its effect on image quality. The intent is to provide the optical engineer with a measure of the sensitivity of image quality to various surface characteristics. The paper will highlight some of the unique modeling features of the code, and illustrate some system examples.

Noll, R. J.↗

DOE OSTI2021

General relativistic MHD simulations of non-thermal flaring in Sagittarius A*

Sgr A* exhibits regular variability in its multiwavelength emission, including daily X-ray flares and roughly continuous near-infrared (NIR) flickering. The origin of this variability is still ambiguous since both inverse Compton and synchrotron emission are possible radiative mechanisms. The underlying particle distributions are also not well constrained, particularly the non-thermal contribution. In this work, we employ the GPU-accelerated general relativistic magnetohydrodynamics code H-AMR to perform a study of flare flux distributions, including the effect of particle acceleration for the first time in high-resolution 3D simulations of Sgr A*. For the particle acceleration, we use the general relativistic ray-tracing code bhoss to perform the radiative transfer, assuming a hybrid thermal+non-thermal electron energy distribution. We extract ~60 h light curves in the sub-millimetre, NIR and X-ray wavebands, and compare the power spectra and the cumulative flux distributions of the light curves to statistical descriptions for Sgr A* flares. Our results indicate that non-thermal populations of electrons arising from turbulence-driven reconnection in weakly magnetized accretion flows lead to moderate NIR and X-ray flares and reasonably describe the X-ray flux distribution while fulfilling multiwavelength flux constraints. These models exhibit high rms per cent amplitudes, $\gtrsim 150{{\ \rm per\ cent}}$ both in the NIR and the X-rays, with changes in the accretion rate driving the 230 GHz flux variability, in agreement with Sgr A* observations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

MPACT 4.4 Theory Manual

MPACT is a three-dimensional (3D) full-core neutron transport code capable of calculating subpin power distributions. Calculations are based on the Boltzmann transport equation for neutron fluxes for problems in which the detailed geometrical configuration of fuel components such as the pellet and cladding are explicitly retained. The cross-section data needed for the neutron transport calculation are obtained directly from a multigroup cross section library, which has traditionally been used by lattice physics codes to generate few-group homogenized cross sections for nodal core simulators. Hence, MPACT assumes neither a priori homogenization nor group condensation for the full core spatial solution. The 3D MPACT transport solution can be obtained using the method of characteristics (MOC), which employs discrete ray tracing within each fuel pin. However, for practical reactor applications, the direct application of MOC to 3D core configurations requires an excessive amount of memory and computing time due to the very large number of rays. For practical 3D full-core calculations, MPACT commonly uses an approximate “2D/1D” method that treats the radial (x and y) variables differently from the axial (z) variable. In particular, the radial dependence of the solution is calculated using transport theory, and the axial dependence is calculated using diffusion or P 3 theory. The 2D/1D method requires the core to be divided into a vertical stack of axial slices with a thickness of Δ z ≈ 5–10 cm. Each axial slice is divided radially into coarse spatial cells with boundaries that usually constitute the pin cell boundaries, for which Δ x = Δ y ≈ 1.5 cm. Then, each coarse radial cell (pin cell) is divided into 50–100 fine radial cells, which resolve the angular flux in the fuel, cladding, and moderator regions.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

NASA NTRS1992

Modelling of capillary optics as a focussing hard X-ray concentrator

The development of glass microcapillary arrays by Kumakhov and co-workers in the Soviet Union suggests that it is possible to construct novel devices for concentrating and focussing X-ray beams. Hypothetical focussing concentrators made up of capillary arrays have been configured to operate over a broad range of X-ray energy and its characteristics have been studied with a Monte Carlo ray tracing code. These modeling results indicate that the concentrators would have significant effective area up to 100 keV while their dimensions are similar to conventional grazing incidence telescopes that operate in the soft X-ray band.

Gorenstein, P.↗

DOE OSTI2021

A model investigation of the impact of lower hybrid wave scattering angle on current drive profile in EAST and Alcator C-Mod

Lower hybrid current drive (LHCD) is beneficial for developing a steady-state operation scenario in a tokamak. This paper conducts a modeling investigation to identify an optimum rotation angle of the initial lower hybrid perpendicular (to the background magnetic field $\overrightarrow{B}$) wavevector for best matching the experimental RF current profile. It is hypothesized that central RF power deposition widely observed in the present-day LHCD experiments arises from wave scattering by turbulence. In a standard model without considering such interactions, the predicted power deposition profile is generally broad with off-axis peaking, not in agreement with experimental observations. A heuristic approach is adopted by introducing a spectral broadening mechanism by modifying the initial orientation of the perpendicular wavevector. The ray-tracing/Fokker–Planck solver GENRAY/CQL3D is utilized within the python-based π-scope framework. A focus is given to identify the perpendicular wavenumber orientation angle with respect to the magnetic surface normal vector at the initial ray location. Our modeling study shows that rotating the perpendicular wavevector in such a way as to increase the initial poloidal component is effective in reproducing the centrally peaked current profile observed in normal shear plasmas on both EAST and C-Mod. These waves can readily be absorbed to the central plasma, which reduces the sensitivity of the power deposition profile to a slight change of the plasma condition. The same approach is also found to help broaden the off-axis power deposition profile in a reverse-shear EAST plasma, leading to a better agreement with the experiment. The results presented here suggest that spectral modification arising from edge density fluctuations in a tokamak may need to be considered in understanding wave propagation and absorption. A further experimental and theoretical/modeling study is vital as a reverse approach is adopted in this study. Finally, our work suggests that mitigation or control measures are critical for parasitic effects occurring on the first pass in a reactor regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS2010

Impact of Spacecraft Shielding on Direct Ionization Soft Error Rates for sub-130 nm Technologies

We use ray tracing software to model various levels of spacecraft shielding complexity and energy deposition pulse height analysis to study how it affects the direct ionization soft error rate of microelectronic components in space. The analysis incorporates the galactic cosmic ray background, trapped proton, and solar heavy ion environments as well as the October 1989 and July 2000 solar particle events.

Pellish, Jonathan A.↗

NASA NTRS2010

Impact of Spacecraft Shielding on Direct Ionization Soft Error Rates for Sub-130 nm Technologies

Pellish, Jonathan A.↗

NASA NTRS1994

The global atmospheric response to low-frequency tropical forcing: Zonally averaged basic states

The extratropical response to localized, low-frequency tropical forcing is examined using a linearized, non-divergent barotropic model on a sphere. Zonal-mean basic states characterized by solid-body rotation or critical latitudes are considered. An analytical analysis based on WKB and ray tracing methods shows that, in contrast to stationary Rossby waves, westward moving, low-frequency Rossby waves can propagate through the tropical easterlies into the extratropics. It is shown analytically that the difference between the stationary and low-frequency ray paths is proportional to the forcing frequency and inversely proportional to the zonal wavenumber cubed. An expression for the disturbance amplitude is derived that shows the ability of the forced waves to maintain their strength well into middle latitudes depends on their meridional wave scale and northward group velocity, both of which are functions of the slowly varying background flow. A local energetics analysis shows that the combination of energy dispersion from the forcing region and energy extraction from the equatorward flank of the midlatitude jet produces disturbances that have the greatest impact on the extratropical circulation. Under the assumption that the forcing amplitude is independent of frequency, this impact is largest when the tropical forcing period is in the range 10-20 days.

Li, Long↗