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At least 307 records · Page 17

All sources NASA NTRS DOE OSTI

DOE OSTI2015

Long-term operation of surface high-harmonic generation from relativistic oscillating mirrors using a spooling tape

Surface high-harmonic generation in the relativistic regime is demonstrated as a source of extreme ultra-violet (XUV) pulses with extended operation time. Relativistic high-harmonic generation is driven by a frequency-doubled high-power Ti:Sapphire laser focused to a peak intensity of 3·1019 W/cm2 onto spooling tapes. We demonstrate continuous operation over up to one hour runtime at a repetition rate of 1 Hz. Harmonic spectra ranging from 20 eV to 70 eV (62 nm to 18 nm) were consecutively recorded by an XUV spectrometer. An average XUV pulse energy in the µJ range is measured. With the presented setup, relativistic surface high-harmonic generation becomes a powerful source of coherent XUV pulses that might enable applications in, e.g. attosecond laser physics and the seeding of free-electron lasers, when the laser issues causing 80-% pulse energy fluctuations are overcome.

42 ENGINEERING↗

DOE OSTI2017

Quasi-supercontinuum source in the extreme ultraviolet using multiple frequency combs from high-harmonic generation

A quasi-supercontinuum source in the extreme ultraviolet (XUV) is demonstrated using a table-top femtosecond laser and a tunable optical parametric amplifier (OPA) as a driver for high-harmonic generation (HHG). The harmonic radiation, which is usually a comb of odd multiples of the fundamental frequency, is generated by near-infrared (NIR) laser pulses from the OPA. A quasi-continuous XUV spectrum in the range of 30 to 100 eV is realized by averaging over multiple harmonic comb spectra with slightly different fundamental frequencies and thus different spectral spacing between the individual harmonics. The driving laser wavelength is swept automatically during an averaging time period. With a total photon flux of 4×10 9 photons/s in the range of 30 eV to 100 eV and 1×10 7 photons/s in the range of 100 eV to 200 eV, the resulting quasi-supercontinuum XUV source is suited for applications such as XUV coherence tomography (XCT) or near-edge absorption fine structure spectroscopy (NEXAFS).

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2026

Harmonic suppression gratings for soft X-ray monochromators

We describe an approach to harmonic suppression in soft X-ray monochromators by engineering the reflection grating’s diffraction pattern to approximate a sinusoidal amplitude. At synchrotron and free-electron laser sources, X-ray beamlines powered by insertion devices produce a spectrum containing harmonic photon energies that can couple unwanted light into experiments. Beamlines in the soft X-ray energy range (100 eV to 2 keV) commonly employ energy-filtering elements to suppress these harmonics. Available approaches tend to be inefficient, significantly reducing the transmitted power. We show that with pseudo-grayscale binary halftone patterns, gratings can approximate a sinusoidal amplitude and suppress higher diffraction orders. Prototype demonstrations of lithographically fabricated gratings were conducted on a soft X-ray beamline with photon energies of 110 eV and 330 eV. Relative to a square-wave amplitude grating, the third-harmonic intensity was reduced by a factor of 9.0 with a first-order efficiency reduction of 38%.

Goldberg, Kenneth A. [Lawrence Berkeley National L↗

DOE OSTI2021

Two-dimensional phase cartography for high-harmonic spectroscopy

Extremely nonlinear spectroscopy based on high-order-harmonic generation has become a powerful investigation method for attosecond dynamics in gas and solid targets. In particular, the phase of harmonic emission was shown to carry profound insight into atomic and molecular structure and dynamics. However, current techniques offer phase measurements only along specific directions, thus providing partial characterization. Here we report on a new approach combining optical and quantum interferometers measuring along two dimensions the intensity and phase of harmonic emission from aligned molecules in the exact same experimental conditions. This two-dimensional cartography technique measures the phase with no arbitrary offset and no uncertainty on its sign. Measurements along different dimensions can be combined in two ways: either a single mapping or a redundant mapping allowing high-precision phase recovery using a Shack–Hartmann-like algorithm. We demonstrate both methods in a nitrogen test case, which allows disentangling structural and dynamical effects. Two-dimensional phase cartography paves the way to high-resolution high-harmonic spectroscopy for applications such as quantum orbital tomography and attosecond charge migration in molecules.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2023

Beam test of a harmonic kicker cavity

A harmonically resonant kicker cavity designed for beam exchange in a circulator cooler was built and successfully tested at the Upgraded Injector Test Facility (UITF) at Jefferson Lab. This type of cavity is being considered for the injection scheme of the Rapid Cycling Synchrotron at the Electron-Ion Collider, where the spacing of neighboring bunches demands very short kicks. Operating with five transversely deflecting modes simultaneously that resonate at 86.6 MHz and consecutive odd harmonics thereof, the prototype cavity selectively deflects 1 of 11 electron bunches while leaving the others unperturbed. An RF driver was developed to synthesize phase- and amplitude-controlled harmonic signals and combine them to drive the cavity while also separating the modes from a field-probe antenna for RF feedback and dynamic tuning. Beam deflection was measured by sweeping the cavity phase; the deflection waveform agrees with expectations, having sub-nanosecond rise and fall times. No emittance increase is observed. Harmonically resonant cavities like the one described provide a new capability for injection and extraction at circulators and rings.

Bruker, M.W.↗

DOE OSTI2023

Harmonic Slip-Stacking

Particle accelerators employ slip-stacking configurations to store two particle beams with disparate momenta within a single ring. Additionally, A novel slip-stacking configuration employing a harmonic RF cavity was proposed and studied. Anticipated benefits of the harmonic cavity include mitigating parametric resonances, minimizing emittance growth, and significantly expanding the stable longitudinal phase-space area. By surpassing the requirements of PIP-II operation, the harmonic RF cavity will support extending slip-stacking operation for subsequent beam power upgrades of Main Injector, including a proposed cycle rate improvement. Our ongoing research will verify the simulation of harmonic slip-stacking (HSS) operation under RF phase-errors, such as those causes by beam-loading effects.

Habibeh, Mohammad↗

DOE OSTI2018

A protocol for an intercomparison of biodiversity and ecosystem services models using harmonized land-use and climate scenarios

Abstract. To support the assessments of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), the IPBES Expert Group on Scenarios and Models is carrying out an intercomparison of biodiversity and ecosystem services models using harmonized scenarios (BES-SIM). The goals of BES-SIM are (1) to project the global impacts of land-use and climate change on biodiversity and ecosystem services (i.e., nature's contributions to people) over the coming decades, compared to the 20th century, using a set of common metrics at multiple scales, and (2) to identify model uncertainties and research gaps through the comparisons of projected biodiversity and ecosystem services across models. BES-SIM uses three scenarios combining specific Shared Socio-economic Pathways (SSPs) and Representative Concentration Pathways (RCPs) – SSP1xRCP2.6, SSP3xRCP6.0, SSP5xRCP8.6 – to explore a wide range of land-use change and climate change futures. This paper describes the rationale for scenario selection, the process of harmonizing input data for land use, based on the second phase of the Land Use Harmonization Project (LUH2), and climate, the biodiversity and ecosystem services models used, the core simulations carried out, the harmonization of the model output metrics, and the treatment of uncertainty. The results of this collaborative modeling project will support the ongoing global assessment of IPBES, strengthen ties between IPBES and the Intergovernmental Panel on Climate Change (IPCC) scenarios and modeling processes, advise the Convention on Biological Diversity (CBD) on its development of a post-2020 strategic plans and conservation goals, and inform the development of a new generation of nature-centred scenarios.

58 GEOSCIENCES↗

NASA NTRS1971

Determination of nonlinear resistance voltage-current relationships by measuring harmonics

Test configuration measures harmonic signal amplitudes generated in nonlinear resistance. Vacuum-type voltmeter measures low frequency sinusoidal input signal amplitude and wave-analyzer measures amplitude of harmonic signals generated in junction. Input signal harmonics amplitude must not exceed that of harmonics generated in nonlinear resistance.

Stafford, J. M.↗

NASA NTRS1976

Nonlinear interaction between two electrostatic harmonics in a plasma

The problem of harmonic and subharmonic generation of electrostatic waves in a general collisionless plasma is treated using coupled-mode theory based on two time scales. A novel feature is that one of the two interacting waves may be a negative-energy wave. Since the model describing the medium need not be specified, only a general linear and nonlinear conductivity or an equivalent description is required. Just by invoking wave-energy conservation, the coupled-mode equations are obtained in such a way that unequivocal conclusions can be drawn. When both waves have positive energy, they exchange part of it in a periodic fashion, provided that both have some energy initially. If initially all the energy is in the fundamental, all of it will eventually end up (irreversibly) in the second harmonic. If all the energy is in the harmonic initially, no generation of the fundamental (or subharmonic) will take place. If one of the two waves is a negative-energy wave, an explosive instability develops, regardless of initial values. For comparable conditions, the instability time depends on whether the negative-energy wave is in the fundamental or in the upper harmonic.

Verheest, F.↗

NASA NTRS1978

Application of higher harmonic blade feathering for helicopter vibration reduction

Higher harmonic blade feathering for helicopter vibration reduction is considered. Recent wind tunnel tests confirmed the effectiveness of higher harmonic control in reducing articulated rotor vibratory hub loads. Several predictive analyses developed in support of the NASA program were shown to be capable of calculating single harmonic control inputs required to minimize a single 4P hub response. In addition, a multiple-input, multiple-output harmonic control predictive analysis was developed. All techniques developed thus far obtain a solution by extracting empirical transfer functions from sampled data. Algorithm data sampling and processing requirements are minimal to encourage adaptive control system application of such techniques in a flight environment.

Powers, R. W.↗

NASA NTRS1981

Spherical harmonic analysis of a model-generated climatology

Monthly mean fields of 850 mb temperature (T850), 500 mb geopotential height (G500) and sea level pressure (SLP) were generated in the course of a five-year climate simulation run with a global general circulation model. Both the model-generated climatology and an observed climatology were subjected to spherical harmonic analysis, with separate analyses of the globe and the Northern Hemisphere. Comparison of the dominant harmonics of the two climatologies indicates that more than 95% of the area-weighted spatial variance of G500 and more than 90% of that of T850 are explained by fewer than three components, and that the model adequately simulates these large-scale characteristics. On the other hand, as many as 25 harmonics are needed to explain 95% of the observed variance of SLP, and the model simulation of this field is much less satisfactory. The model climatology is also evaluated in terms of the annual cycles of the dominant harmonics.

Christidis, Z. D.↗

NASA NTRS1982

A harmonic analysis method for unsteady transonic flow and its application to the flutter of airfoils

A finite difference method for solving the unsteady transonic flow about harmonically oscillating wings is investigated. The procedure is based on separating the velocity potential into steady and unsteady parts and linearizing the resulting unsteady differential equation for small disturbances. The differential equation for the unsteady velocity potential is linear with spatially varying coefficients and with the time variable eliminated by assuming harmonic motion. A study is presented of the shock motion associated with an oscillating airfoil and its representation by the harmonic procedure. The effects of the shock motion and the resulting pressure pulse are shown to be included in the harmonic pressure distributions and the corresponding generalized forces. Analytical and experimental pressure distributions for the NACA 64A010 airfoil are compared for Mach numbers of 0.75, 0.80 and 0.842. A typical section, two-degree-of-freedom flutter analysis of a NACA 64A010 airfoil is performed. The results show a sharp transonic bucket in one case and abrupt changes in instability modes.

Ehlers, F. E.↗

NASA NTRS1983

Ordinary mode auroral kilometric radiation, with harmonics, observed by ISIS 1

Topside-sounder receiver observations by ISIS 1 that reveal examples of o-mode auroral kilometric radiation (AKR) are presented. They correspond to locations outside of the low density source region of intense AKR x-mode emission. The propagation modes are identified by comparing the natural radiation wave cutoffs with the local resonant and wave cutoff phenomena stimulated by the sounder transmitter. The o-mode AKR is the dominant emission in these regions of relatively high electron density, but it is considerably weaker than the intense x-mode AKR observed to emanate from low density cavities above the auroral regions. In addition to the fundamental o-mode, 2nd and 3rd harmonic bands of radiation have also been detected. Harmonics associated with these o-mode AKR are less intense than the harmonics associated with x-mode AKR. It is difficult to explain the variety of harmonic AKR observations (x as well as o-mode) based on present AKR theories.

Benson, R. F.↗

NASA NTRS1983

Emissions of second-harmonic auroral kilometric radiation

The cyclotron maser theory of Wu and Lee (1979) is used in treating second-harmonic auroral kilometric radiation (AKR). Good agreement is obtained with the ISIS 1 observation reported by Benson (1982). It is found that when the ratio of the electron plasma frequency to the electron gyrofrequency is less than 0.3, the fundamental AKR prevails over the second-harmonic AKR. When the value of this ratio is greater than or approximately equal to 0.3, the fundamental AKR may become weaker than the second-harmonic AKR, and when it is greater than 0.3 the fundamental AKR may diminish. It is also found that the second harmonic AKR with frequencies below twice the electron gyro-frequency can propagate downward.

Wu, C. S.↗

NASA NTRS1984

Ordinary mode auroral kilometric radiation, with harmonics, observed by ISIS 1

Benson, R. F.↗

NASA NTRS1986

Application of higher harmonic blade feathering on the OH-6A helicopter for vibration reduction

The design, implementation, and flight test results of higher harmonic blade feathering for vibration reduction on the OH-6A helicopter are described. The higher harmonic control (HHC) system superimposes fourth harmonic inputs upon the stationary swashplate. These inputs are transformed into 3P, 4P and 5P blade feathering angles. This results in modified blade loads and reduced fuselage vibrations. The primary elements of this adaptive vibration suppression system are: (1) acceleration transducers sensing the vibratory response of the fuselage; (2) a higher harmonic blade pitch actuator system; (3) a flightworthy microcomputer, incorporating the algorithm for reducing vibrations, and (4) a signal conditioning system, interfacing between the sensors, the microcomputer and the HHC actuators. The program consisted of three distinct phases. First, the HHC system was designed and implemented on the MDHC OH-6A helicopter. Then, the open loop, or manual controlled, flight tests were performed, and finally, the closed loop adaptive control system was tested. In 1983, one portion of the closed loop testing was performed, and in 1984, additional closed loop tests were conducted with improved software. With the HHC system engaged, the 4P pilot seat vibration levels were significantly lower than the baseline ON-6A levels. Moreover, the system did not adversely affect blade loads or helicopter performance. In conclusion, this successful proof of concept project demonstrated HHC to be a viable vibration suppression mechanism.

Straub, F. K.↗

NASA NTRS1989

A test of a modified algorithm for computing spherical harmonic coefficients using an FFT

The Dilts (1985) algorithm for computing the spherical harmonic expansion coefficients for a function on a sphere, on the basis of a two-dimensional FFT, is presently modified, tested, and found to eliminate problems of overflow and large storage requirements associated with the encounter of harmonic degree values greater than 16. Results from timing tests show the Dilts program to be impractical, however, for the computation of spherical harmonic expansion coefficients for large harmonic degree values.

Elowitz, Mark↗

NASA NTRS1989

On the excitation of cyclotron harmonic waves by newborn heavy ions

Wave measurements in planetary foreshocks and cometary environments show the sporadic occurrence of magnetic spectra with harmonic structure related to ion-cyclotron frequencies. Dilute populations of anisotropic and/or drifting charged particles can excite obliquely propagating modes with spacecraft frequencies close to the observed harmonics. Previous analyses of this generation mechanism are extended to drifting and nondrifting loss-cone-type distributions of heavy ions in a dense hydrogen magnetoplasma, characterizing the complex (real frequency and growth rate) dispersion, polarization, and compressibility of the unstable cyclotron harmonic waves. Solution of the full kinetic dispersion equation shows that it is possible to attain harmonic excitation, both in the drifting and nondrifting regimes. However, the bandwidth inherent to frequency Doppler shifts of obliquely propagating waves might preclude the observation of spectral structure in the spacecraft frame. The Giotto observations in the upstream region of comet Halley provide a reference to discuss the results.

Brinca, Armando L.↗