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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

Fast Transient And Spatially Non-Homogenous Accident Analysis Of Two-Dimensional Cylindrical Nuclear Reactor

The research about fast transient and spatially non-homogenous nuclear reactor accident analysis of two-dimensional nuclear reactor has been done. This research is about prediction of reactor behavior is during accident. In the present study, space-time diffusion equation is solved by using direct methods which consider spatial factor in detail during nuclear reactor accident simulation. Set of equations that obtained from full implicit finite-difference discretization method is solved by using iterative methods ADI (Alternating Direct Implicit). The indication of accident is decreasing macroscopic absorption cross-section that results large external reactivity. The power reactor has a peak value before reactor has new balance condition. Changing of temperature reactor produce a negative Doppler feedback reactivity. The reactivity will reduce excess positive reactivity. Temperature reactor during accident is still in below fuel melting point which is in secure condition.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2011

Electron Scale Solar Wind Turbulence: Cluster Observations and Theoretical Modeling

Turbulence at MagnetoHydroDynamics (MHD) scales of the solar wind has been studied for more than three decades, using data analyzes, theoretical and numerical modeling. However smaller scales have not been explored until very recently. Here, we review recent results on the first observation of cascade and dissipation of the solar wind turbulence at the electron scales. Thanks to the high resolution magnetic and electric field data of the Cluster spacecraft, we computed the spectra of turbulence up to {approx}100 Hz (in the spacecraft reference frame) and found two distinct breakpoints in the magnetic spectrum at 0.4 Hz and 35 Hz, which correspond, respectively, to the Doppler-shifted proton and electron gyroscales, f{sub {rho}p} and f{sub {rho}e}. Below f{sub {rho}p} the spectrum follows a Kolmogorov scaling f{sup -1.62}, typical of spectra observed at 1 AU. Above f{sub {rho}p} a second inertial range is formed with a scaling f{sup -2.3} down to f{sub {rho}e}. Above f{sub {rho}e} the spectrum has a steeper power law {approx}f{sup -4.1} down to the noise level of the instrument. Solving numerically the linear Maxwell-Vlasov equations combined with recent theoretical predictions of the Gyro-Kinetic theory, we show that the present results are fully consistent with a scenario of a quasi-two-dimensional cascade into Kinetic Alfven modes (KAW).

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

The photodissociation dynamics of tetrachloroethylene

We present a direct current slice imaging study of tetrachloroethylene (C{sub 2}Cl{sub 4}) photodissociation, probing the resulting ground state Cl ({sup 2}P{sub 3/2}) and spin-orbit excited state Cl* ({sup 2}P{sub 1/2}) products. We report photofragment images, total translational energy distributions and the product branching ratio of Cl*/Cl following dissociation at 235 and 202 nm, obtained using a two-color reduced-Doppler dissociation/probe. Near 235 nm, the Cl translational energy distribution shows a peak at the limit of the available energy, indicating a direct dissociation through a {sigma}*(C-Cl) (leftarrow){pi} (C=C) transition, which is superimposed on a broader underlying distribution. The ground state Cl image and associated translational energy distribution at 202 nm is broad and peaked at lower energy, suggesting either internal conversion to the ground state or a lower excited state prior to dissociation. The Cl* images are similarly broad at both wavelengths. The branching ratio is presented as a function of recoil energy, but after integration shows a near-statistical average of Cl:Cl* as 70:30 at both wavelengths. All the images are largely isotropic, with anisotropy parameters ({beta}) of 0.05 {+-} 0.03.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Plasma-wall interaction studies with optimized laser-produced jets

The production of the laser-produced plasma jets at burnt-through low-Z foils was optimized by using three-frame interferometry. When striking secondary targets, these jets of energetic particles represent an efficient tool for the investigation of transient phenomena at surfaces of the plasma-exposed solids. Two sets of precisely measured x-ray spectroscopic data demonstrate diagnostic potential of the collimated jets in the plasma-wall interaction studies: Blue Doppler shifts of the Al jet self-emission visualize ion deceleration in the near-wall region. Local depressions found in Al Ly{gamma} profiles emitted from Al/Si(PMMA) targets indicate charge exchange between the Al XIII and fully stripped C ions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Measurement of absolute E2 transition strengths in {sup 176}W: Signatures for a rapid shape change

The X(5) symmetry describes nuclei at the critical point of the shape phase transition from axially deformed rotor nuclei to spherical vibrators. {sup 150}Nd, {sup 152}Sm, and {sup 154}Gd were the first nuclei where the predicted characteristics of the X(5) symmetry were observed. Later it was shown that also {sup 176,178,180}Os can be successfully described with the X(5) symmetry.In the close vicinity of shape phase transitions one expects strongly changing nuclear shapes. In the X(5) region around A = 150 this was observed for nuclei with different neutron numbers, whereas in the X(5) region around A = 180 this is to be expected for different proton numbers. The aim of the work presented here is the confirmation of a rapid shape change for nuclei close to {sup 178}Os. Besides the knowledge on the level scheme of the nuclei of interest, especially absolute E2 transition strengths are crucial for the interpretation of nuclear structure. Prolate deformation is expected for {sup 176}W. Thus we performed a recoil distance Doppler shift (RDDS) measurement on {sup 176}W to measure E2 transition strengths from level lifetimes. The experiment was performed at the Cologne FN TANDEM accelerator with the Cologne coincidence plunger with the reaction {sup 169}Dy({sup 16}O,4n){sup 176}W and a beam energy of 80 MeV. We will present our experimental results and relate them to data on the neighboring nuclei {sup 178}Os and {sup 182}Pt. The results will be discussed in the framework of nuclear shape transitions in this mass region and compared to calculations with both the Interacting Boson Model (IBM) and the GCM.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Onset of collectivity in Neutron-Rich iron isotopes: Toward a new island of inversion?

The lifetimes of the first excited 2{sup +} states in {sup 62}Fe and {sup 64}Fe have been measured for the first time using the recoil-distance Doppler shift technique, at GANIL. A {sup 238}U beam of 6.5 AMeV impinged on {sup 64}Ni target, and the target like products were slowed down by a degrader foil positioned at micrometer distance downstream of the target and identified in the VAMOS spectrometer on an event-by-event basis. The lifetimes were then determined from the intensities of the degraded and fully Doppler shifted components of the 2{sup +}{yields}0{sup +} transition detected in EXOGAM detectors positioned at backward angles.The resulting lifetimes show a steep increase of the B(E2) values of the first excited 2{sup +} state from {sup 62}Fe to {sup 64}Fe. A comparison with shell model calculations shows that the onset of collectivity is related to the occupation of neutron intruder orbitals. The large B(E2) value for {sup 64}Fe is only reproduced if the valence space includes both the neutron g{sub 9/2} and d{sub 5/2} orbitals. The transition from spherical {sup 68}Ni to more proton-deficient N 40 isotones has some similarity with the island of inversion around {sup 32}Mg. The developing quadrupole collectivity can in both cases be related to the occupation of neutron intruder orbitals which are at the same time quasi-SU(3) partners: (f{sub 7/2}, p{sub 3/2}) for {sup 32}Mg and (g{sub 9/2}, d{sub 5/2}) for the neutron-rich Fe.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Beam Homogeneity Dependence on the Magnetic Filter Field at the IPP Test Facility MANITU

The homogeneity of the extracted current density from the large RF driven negative hydrogen ion sources of the ITER neutral beam system is a critical issue for the transmission of the negative ion beam through the accelerator and the beamline components. As a first test, the beam homogeneity at the IPP long pulse test facility MANITU is measured by means of the divergence and the stripping profiles obtained with a spatially resolved Doppler-shift spectroscopy system. Since MANITU is typically operating below the optimum perveance, an increase in the divergence corresponds to a lower local extracted negative ion current density if the extraction voltage is constant. The beam H{sub {alpha}} Doppler-shift spectroscopy is a rather simple tool, as no absolute calibration - both for the wavelength and the emission - is necessary. Even no relative calibration of the different used lines of sight is necessary for divergence and stripping profiles as these quantities can be obtained by the line broadening of the Doppler-shifted peak and the ratio of the integral of the stripping peak to the integral of the Doppler-shifted peak, respectively. The paper describes the H{sub {alpha}} MANITU Doppler-shift spectroscopy system which is now operating routinely and the evaluation methods of the divergence and the stripping profiles. Beam homogeneity measurements are presented for different extraction areas and magnetic filter field configurations both for Hydrogen and Deuterium operation; the results are compared with homogeneity measurements of the source plasma. The stripping loss measurements are compared with model calculations.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

First neutral beam injection experiments on KSTAR tokamak

The first neutral beam (NB) injection system of the Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak was partially completed in 2010 with only 1/3 of its full design capability, and NB heating experiments were carried out during the 2010 KSTAR operation campaign. The ion source is composed of a JAEA bucket plasma generator and a KAERI large multi-aperture accelerator assembly, which is designed to deliver a 1.5 MW, NB power of deuterium at 95 keV. Before the beam injection experiments, discharge, and beam extraction characteristics of the ion source were investigated. The ion source has good beam optics in a broad range of beam perveance. The optimum perveance is 1.1-1.3 {mu}P, and the minimum beam divergence angle measured by the Doppler shift spectroscopy is 0.8 deg. The ion species ratio is D{sup +}:D{sub 2}{sup +}:D{sub 3}{sup +}= 75:20:5 at beam current density of 85 mA/cm{sup 2}. The arc efficiency is more than 1.0 A/kW. In the 2010 KSTAR campaign, a deuterium NB power of 0.7-1.5 MW was successfully injected into the KSTAR plasma with a beam energy of 70-90 keV. L-H transitions were observed within a wide range of beam powers relative to a threshold value. The edge pedestal formation in the T{sub i} and T{sub e} profiles was verified through CES and electron cyclotron emission diagnostics. In every deuterium NB injection, a burst of D-D neutrons was recorded, and increases in the ion temperature and plasma stored energy were found.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Diamagnetism of rotating plasma

Diamagnetism and magnetic measurements of a supersonically rotating plasma in a shaped magnetic field demonstrate confinement of plasma pressure along the magnetic field resulting from centrifugal force. The Grad-Shafranov equation of ideal magnetohydrodynamic force balance, including supersonic rotation, is solved to confirm that the predicted angular velocity is in agreement with spectroscopic measurements of the Doppler shifts.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Experimental quiescent drifting dusty plasmas and temporal dust acoustic wave growth

We report on dust acoustic wave growth rate measurements taken in a dc (anode glow) discharge plasma device. By introducing a mesh with a variable bias 12-17 cm from the anode, we developed a technique to produce a drifting dusty plasma. A secondary dust cloud, free of dust acoustic waves, was trapped adjacent to the anode side of the mesh. When the mesh was returned to its floating potential, the secondary cloud was released and streamed towards the anode and primary dust cloud, spontaneously exciting dust acoustic waves. The amplitude growth of the excited dust acoustic waves was measured directly along with the wavelength and Doppler shifted frequency. These measurements were compared to fluid and kinetic dust acoustic wave theories. As the wave growth saturated a transition from linear to nonlinear waves was observed. The merging of the secondary and primary dust clouds was also observed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Lifetime measurement in the proton-unbound nucleus {sup 109}I

The Recoil-Distance Doppler-shift method has been combined with Recoil-Decay Tagging for the first time to measure a lifetime in the proton-unbound nucleus {sup 109}I. The lifetime value was determined using the Differential Decay-Curve method in singles mode. The result has been compared to theoretical shell-model calculations in order to better understand the nature of unbound valence nucleons at the proton drip line.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Beam emission spectroscopy turbulence imaging system for the MAST spherical tokamak

A new beam emission spectroscopy turbulence imaging system has recently been installed onto the MAST spherical tokamak. The system utilises a high-throughput, direct coupled imaging optics, and a single large interference filter for collection of the Doppler shifted D{sub {alpha}} emission from the {approx}2 MW heating beam of {approx}70 keV injection energy. The collected light is imaged onto a 2D array detector with 8 x 4 avalanche photodiode sensors which is incorporated into a custom camera unit to perform simultaneous 14-bit digitization at 2 MHz of all 32 channels. The array is imaged at the beam to achieve a spatial resolution of {approx}2 cm in the radial (horizontal) and poloidal (vertical) directions, which is sufficient for detection of the ion-scale plasma turbulence. At the typical photon fluxes of {approx}10{sup 11} s{sup -1} the achieved signal-to-noise ratio of {approx}300 at the 0.5 MHz analogue bandwidth is sufficient for detection of relative density fluctuations at the level of a few 0.1%. The system is to be utilised for the study of the characteristics of the broadband, ion-scale turbulence, in particular its interaction with flow shear, as well as coherent fluctuations due to various types of MHD activity.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

Optic-microwave mixing velocimeter for superhigh velocity measurement

The phenomenon that a light beam reflected off a moving object experiences a Doppler shift in its frequency underlies practical interferometric techniques for remote velocity measurements, such as velocity interferometer system for any reflector (VISAR), displacement interferometer system for any reflector (DISAR), and photonic Doppler velocimetry (PDV). While VISAR velocimeters are often bewildered by the fringe loss upon high-acceleration dynamic process diagnosis, the optic-fiber velocimeters such as DISAR and PDV, on the other hand, are puzzled by high velocity measurement over 10 km/s, due to the demand for the high bandwidth digitizer. Here, we describe a new optic-microwave mixing velocimeter (OMV) for super-high velocity measurements. By using currently available commercial microwave products, we have constructed a simple, compact, and reliable OMV device, and have successfully obtained, with a digitizer of bandwidth 6 GH only, the precise velocity history of an aluminum flyer plate being accelerated up to 11.2 km/s in a three stage gas-gun experiment.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Nonlinear relativistic single-electron Thomson scattering power spectrum for incoming laser of arbitrary intensity

The classical nonlinear incoherent Thomson scattering power spectrum from a single relativistic electron with incoming laser radiation of any intensity, investigated numerically by the present authors in a previous publication, displayed both an approximate quadratic behavior in frequency and a redshift of the power spectrum for high intensity incoming radiation. The present work is devoted to justify, in a more general setup, those numerical findings. Those justifications are reinforced by extending suitably analytical approaches, as developed by other authors. Moreover, our analytical treatment exhibits differences between the Doppler-like frequencies for linear and circular polarization of the incoming radiation. Those differences depend nonlinearly on the laser intensity and on the electron initial velocity and do not appear to have been displayed by previous authors. Those Doppler-like frequencies and their differences are validated by new Monte Carlo computations beyond our previuos ones and reported here.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

High resolution ion Doppler spectroscopy at Prairie View Rotamak

A fast ion Doppler spectroscopy (IDS) diagnostic system is installed on the Prairie View Rotamak to measure ion temperature and plasma flow. The diagnostic employs a single channel photomultiplier tube and a Jarrell-Ash 50 monochromator with a diffraction grating line density of 1180 lines/mm, which allows for first order spectra of 200-600 nm. The motorized gear of the monochromator allows spectral resolution of 0.01 nm. Equal IDS measurements are observed for various impurity emission lines of which carbon lines exhibit stronger intensities. Furthermore, the diagnostics is examined in an experiment where plasma experiences sudden disruption and quick recovery. In this case, the IDS measurements show {approx}130% increase in ion temperature. Flow measurements are shown to be consistent with plasma rotation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Density fluctuation measurements by far-forward collective scattering in the MST reversed-field pinch

The multichannel polarimeter-interferometer system on the MST reversed-field pinch can be utilized to measure far-forward collective scattering from electron density fluctuations. The collective scattering system has 11 viewing chords with {approx}8 cm spacing. The source is a 432 {mu}m (694 GHz) far infrared laser and the scattered power is measured using a heterodyne detection scheme. Collective scattering provides a line-integrated measurement of fluctuations within the divergence of the probe beam covering wavenumber range: k{sub Up-Tack} < 1.3 cm{sup -1}, corresponding k{sub Up-Tack }{rho}{sub s} < 1.3 ({rho}{sub s} is the ion-sound Larmor radius), the region of primary interest for turbulent fluctuation-induced transport. The perpendicular wavenumber consists of toroidal, poloidal, and radial contributions, which vary with chord position. Coherent modes associated with tearing instabilities and neutral-beam driven fast particles are observed along with broadband turbulence at frequencies up to 500 kHz. Changes in frequency are consistent with a Doppler shift due to parallel plasma flow.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Isorotation and differential rotation in a magnetic mirror with imposed E Multiplication-Sign B rotation

Doppler spectroscopy of helium impurities in the Maryland Centrifugal Experiment reveals the simultaneous existence of isorotating and differentially rotating magnetic surfaces. Differential rotation occurs at the innermost surfaces and is conjectured to cause plasma voltage oscillations of hundreds of kilohertz by periodically changing the current path inductance. High-speed images show the periodic expulsion of plasma near the mirror ends at the same frequencies. In spite of this, the critical ionization velocity limit is exceeded, with respect to the vacuum field definition, for at least 0.5 ms.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

A high etendue spectrometer suitable for core charge eXchange recombination spectroscopy on ITER

A feasibility study for the use of core charge exchange recombination spectroscopy on ITER has shown that accurate measurements on the helium ash require a spectrometer with a high etendue of 1mm{sup 2}sr to comply with the measurement requirements [S. Tugarinov et al., Rev. Sci. Instrum. 74, 2075 (2003)]. To this purpose such an instrument has been developed consisting of three separate wavelength channels (to measure simultaneously He/Be, C/Ne, and H/D/T together with the Doppler shifted direct emission of the diagnostic neutral beam, the beam emission (BES) signal), combining high dispersion (0.02 nm/pixel), sufficient resolution (0.2 nm), high efficiency (55%), and extended wavelength range (14 nm) at high etendue. The combined measurement of the BES along the same sightline within a third wavelength range provides the possibility for in situ calibration of the charge eXchange recombination spectroscopy signals. In addition, the option is included to use the same instrument for measurements of the fast fluctuations of the beam emission intensity up to 2 MHz, with the aim to study MHD activity.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗