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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Secondary electron generation, emission and transport: Effects on spacecraft charging and NASCAP models

Secondary electrons control a spacecraft's response to a plasma environment. To accurately simulate spacecraft charging, the NASA Charging Analyzer Program (NASCAP) has mathematical models of the generation, emission and transport of secondary electrons. The importance of each of the processes and the physical basis for each of the NASCAP models are discussed. Calculations are presented which show that the NASCAP formulations are in good agreement with both laboratory and space experiments.

Katz, Ira↗
NASA NTRS2005

Angular Distribution of Elastically Scattered Electrons Determined and Its Effect on Collector Performance Computed

It has been demonstrated that the suppression of secondary electron emission significantly improves the performance of electron beam collectors (ref. 1). However, a complete analysis of the effects of secondary electron emission with respect to collector performance has not been possible because of the lack of quantitative data on angular distributions of secondary electrons. Secondary electrons are emitted with energies ranging from near zero to the energy of the incident primary. For our purposes, we define elastically scattered electrons as secondary electrons within 20 percent of the incident energy. Elastically scattered electrons are of great concern because their energy allows them to follow trajectories that can carry them almost anywhere within the vacuum envelope. If these secondaries leave the collector and reenter the slow wave circuit, they can produce undesired signal distortion and oscillation.This apparatus, which was built by Krainsky (ref. 2), was used at the NASA Lewis Research Center to obtain detailed measurements of the angular distributions of elastically scattered secondaries. Data were obtained for three surfaces of significant interest to collector applications: highly polished copper, copper roughened by ion sputtering, and isotropic graphite. Lewis researchers discovered that elastically scattered electrons have a complex angular distribution that is strongly dependent on the atomic number and surface morphology of the target material, as well as the energy and angle of incidence of the primary beam. At low energies, secondary emission from polished copper in the chosen energy range is primarily directed back to the source of primary electrons (backscattering). Forward scattering increases with primary energy until, at high energies, forward scattering dominates the angular distribution. Although back-scattered secondaries dominate the distributions of the textured copper surface, the yield is substantially lower. From the standpoint of secondary emission, isotropic graphite is the most attractive material because it exhibits low yield and little back scattering.

Krainsky, Isay L.↗
DOE OSTI2022

Diagnosing the pedestal magnetic field and magnetohydrodynamics radial structure with pedestal–scrape of layer electron cyclotron emission radiation inversion in H-mode plasma (invited)

Forward modeling is used to interpret inversion patterns of the pedestal–Scrape of Layer (SOL) Electron Cyclotron Emission (ECE) in DIII-D H-mode experiments. The modeling not only significantly improves the ECE data interpretation quality but also leads to the potential measurements of (1) the magnetic field strength |B| at the separatrix, (2) the pedestal |B| evolution during an inter-Edge Localized Mode (ELM) period, and (3) the pedestal Magnetohydrodynamics (MHD) radial structure. The ECE shine-through effect leads to three types of pedestal–SOL radiation inversions that are discussed in this paper. The first type of inversion is the non-monotonic T e,rad profile with respect to the major radius. Using the ECE frequency at the minimum T e,rad , the inversion can be applied to measure the magnetic field |B| at the separatrix and calibrate the mapping of the ECE channels with respect to the separatrix. The second type of inversion refers to the opposite phase between the radiation fluctuations δT e,rad at the pedestal and SOL. This δT e,rad phase inversion is sensitive to density and temperature fluctuations at the pedestal foot and, thus, can be used to qualitatively measure the MHD radial structure. The third type of inversion appears when the pedestal and SOL T e,rad evolve in an opposite trend, which can be used to infer the pedestal |B| field change during an inter-ELM period. Finally, the bandwidth effect on measuring δT e,rad due to pedestal MHD is also investigated in the radiation modeling.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1986

Waves generated during electron beam emissions from the Space Shuttle

Observations from the SEPAC (Space Experiments with Particle Accelerators) experiment on Spacelab 1 Shuttle mission of waves generated during electron beam emissions are presented. The dependence of the wave intensity on the beam parameters and the Shuttle attitude is outlined, and the shape of the wave spectra are discussed. It is found that the noise in the 0.75- to 10 kHz band has a spectral shape that can be characterized by an f exp -n law, and that the VLF signal level depends on the beam angle to the magnetic field, the strongest emissions being observed for parallel beams. These features are found to be consistent with a drift wave instability.

Neubert, T.↗
DOE OSTI2021

Noise suppression for MHD characterization with electron cyclotron emission imaging 1D technique

Significant noise suppression for magnetohydrodynamics (MHD) mode characterization in the spatial and spectral domain is achieved by processing two-dimensional (2D) electron cyclotron emission imaging (ECEI) data with a one-dimensional (1D) ECEI technique using a short time window ($1\;{\text{ms}}$). The technique is applied to detect toroidal Alfven eigenmodes (TAEs) in the temporal spectrum and fit their radial envelope using the data from the DIII-D tokamak W-band 2D ECEI system. Using the data length (time window) of only 1 ${\text{ms}}$, the 1D ECEI can clearly detect the TAEs (~100 ${\text{kHz}}$) on the spectrum, while similar spectrum quality requires ~10 ${\text{ms}}$ data length with the cross power spectrum between two midplane ECEI channels. The 1D ECEI technique also effectively avoids biased fitting when resolving the fine structure of the TAE's radial envelope. The radially spatial resolution of 1D ECEI is constrained by the finite ECE radiation volume of the ECEI receiver. Here, with forward radiation modeling, we find the DIII-D ECEI system can sensitively measure the even parity MHD activities, for which the mode width is >15 mm, and tearing modes (odd parity MHD activities), for which the island full width is >30 mm.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Design of an electron cyclotron emission diagnostics suite for COMPASS Upgrade tokamak

COMPASS Upgrade is a medium size and high field tokamak that is capable of addressing key challenges for reactor grade tokamaks, including power exhaust and advanced confinement scenarios. Electron cyclotron emission will be available among the first diagnostics to provide measurements of high spatial and temporal resolution of electron temperature profiles and electron temperature fluctuation profiles through a radial view. A separate oblique view at 12° from normal will be utilized to study non-thermal electrons. Both the radial and oblique views are envisioned to be located in a wide-angle midplane port, which has dimensions that enable simultaneous hosting of the front-end of their quasi-optical (QO) designs. Each QO design will have an in situ hot calibration source in the front-end to provide standalone and calibrated Te (R,t) measurements. The conceptual design for each QO system, the Gaussian beam analysis, and the details of the diagnostic channels are presented.

Instruments & Instrumentation↗
DOE OSTI2025

Effects of oxidation and impurities in lithium surfaces on the emitting wall plasma sheath

The use of lithium as a surface coating in fusion devices improves the plasma performance, but the change in the wall properties affects the secondary electron emission properties of the material. Lithium oxidizes easily, which drives the emission yield well above unity. We present here simulations demonstrating the change in the sheath structure from monotonic to the nonmonotonic space-charge limited sheath using an energy-dependent data-driven emission model, which self-consistently captures both secondary emission and backscattering populations. Increased secondary electron emission from the material has ramifications for the degradation and erosion of the wall. The results show that the oxidation leads to an increased electron energy flux into the wall and a reduced ion energy flux. The net transfer of energy to the surface is significantly greater for the oxidized case than for the pure lithium case. High backscattering rates of low-energy particles lead to a high re-emission rate at the wall.

Fusion reactors↗
NASA NTRS1987

High-energy particle production in solar flares (SEP, gamma-ray and neutron emissions)

Electrons and ions, over a wide range of energies, are produced in association with solar flares. Solar energetic particles (SEPs), observed in space and near earth, consist of electrons and ions that range in energy from 10 keV to about 100 MeV and from 1 MeV to 20 GeV, respectively. SEPs are directly recorded by charged particle detectors, while X-ray, gamma-ray, and neutron detectors indicate the properties of the accelerated particles (electrons and ions) which have interacted in the solar atmosphere. A major problem of solar physics is to understand the relationship between these two groups of charged particles; in particular whether they are accelerated by the same mechanism. The paper reviews the physics of gamma-rays and neutron production in the solar atmosphere and the method by which properties of the primary charged particles produced in the solar flare can be deduced. Recent observations of energetic photons and neutrons in space and at the earth are used to present a current picture of the properties of impulsively flare accelerated electrons and ions. Some important properties discussed are time scale of production, composition, energy spectra, accelerator geometry. Particular attention is given to energetic particle production in the large flare on June 3, 1982.

Chupp, E. L.↗
NASA NTRS1994

Generation of radiation in solar corona and interplanetary space by energetic electrons

Emissions of electromagnetic waves with frequencies close to the plasma frequency and/or its second harmonic have been frequently observed in the solar corona and interplanetary space. In the past, a number of theories have been put forward to esplain the generation mechanism of the observed radiation. In this paper, a new model is proposed. The essential point of the present theory is that the Langmuir waves amplified as a result of the usual beam instability can lead to two important effects: first, electrostatic waves with frequencies close to twice the plasma frequency can be excited; and second, a significant modification of the dispersion relation can occur, so that these electrostatic waves can naturally change into electomagnetic waves as they propagate in a plasma in which the plasma density decreases spatially. The latter effect is attributed to a mode couplng process. In addition to the second harmonic emission, emission at the fundamental is also briefly discussed. In this case, as in many other theories, the presence of a very low frequency electostatic wave such as the ion-acoustic wave is assumed. The emission process discussed in the present theory stresses the importance of mode coupling and conversion rather than kinetic processes such as a nonlinear wave-wave or wave-particle scattering.

Wu, C. S.↗
DOE OSTI2023

Spectral emission properties of a nitrogen-doped diamond (001) photocathode: Hot electron transport and transverse momentum filtering

The electron emission properties of a single-crystal nitrogen-doped diamond(001) photocathode inserted in a 10 kV DC photoelectron gun are determined using a tunable (235–410 nm) ultraviolet laser radiation source for photoemission from both the back nitrogen-doped substrate face and the front homoepitaxially grown and undoped diamond crystal face. Here, the measured spectral trends of the mean transverse energy and quantum efficiency of the emitted electrons are both anomalous and nonmonotonic, but are shown to be consistent with (i) the known physics of electron photoexcitation from the nitrogen substitution states into the conduction bands of diamond, (ii) the energy position and dispersion characteristics of the conduction bands of diamond in the (001) emission direction, (iii) the effective electron affinity of the crystal faces, (iv) the strong electron-(optical)phonon coupling in diamond, and (v) the associated hot electron transport dynamics under energy equipartition with the optical phonons. Notably, the observed hot electron emission is shown to be restricted parallel to the photocathode surface by the low transverse effective masses of the emitting band states—a transverse momentum filtering effect.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Vehicle charging effects during electron beam emission from the CHARGE-2 experiment

The CHARGE-2 sounding rocket payload has measured the transient and steady-state charging of a spacecraft in LEO during the emission of a low-power electron beam. The electron beam successfully escaped the emitting spacecraft above 240 km, rather than being degraded by the spacecraft's potentials. These potentials were limited to about half of the 1-kV beam accelerating potential at all latitudes, suggesting that the electron beam was able to escape at altitudes down to 160 km. Electrons created from beam-plasma interactions become increasingly important in the return current below 240 km, and increased with decreasing altitude.

Myers, Neil B.↗
NASA NTRS1986

Vehicle charging of the shuttle Orbiter during electron beam emission

The Vehicle Charging And Potential (VCAP) experiment has flown as part of shuttle missions STS-3/OSS-1 in March 1982 and STS-51F/Spacelab-2 in July/August 1985. During these missions, a 1 keV electron beam was emitted with currents of 50, 100 and 150 mA. The Orbiter response to electron beam emission was measured by a charge and current probe located in the payload bay. Examination of these vehicle charging and return current signatures has revealed a variety of unanticipated signatures in addition to several expected results. The principle results are listed and briefly discussed.

Hawkins, J. G.↗
DOE OSTI2024

Electron cyclotron emission detection of neoclassical tearing modes for control for ITER

Successful operation of ITER requires control of magnetic instabilities including neoclassical tearing modes (NTMs) that can degrade confinement and lead to disruption. Low latency detection by electron cyclotron emission (ECE) diagnostics has been demonstrated in a few current experiments. Using a synthetic diagnostic, we demonstrate low latency NTM detection for ITER with plasmas described by ITER IMAS database scenarios and with realistic limitations imposed on the instrumentation by these high temperature scenarios. 2/1 NTMs are detected 430 ms after magnetic island seeding and before island locking. The radiometer configuration was optimized using simulation, and the smallest detectable island size was explored. Island sizes of ∼3 cm are detectable at the 2/1 surface. The simulated signals incorporate recent physics models for island growth and rotation, which show early locking and continued island growth after locking and before disruption. This work determines limits for ITER ECE spatial resolution imposed by relativistic broadening of channels, which informs hardware design. Real-time detection is demonstrated in hardware that is required by ITER, including on an NI PXI-7853R FPGA system. Development of a synthetic diagnostic and details of the hardware will be discussed.

Cyclotron radiation↗
NASA NTRS1993

(abstract)Electron Impact Emission Cross Sections for Modeling UV Auroral and Dayglow Observations of the Upper Atmospheres of Planets

In the upper atmospheres of the Jovian and Terrestrial planets a dominant mechanism for energy transfer occurs through electron collisional processes with neutral species leading to UV radiation. In response to the need for accurate collision cross sections to model spectroscopic observations of planetary systems, JPL has measured in the laboratory emission cross sections and medium resolution spectra of H, H(sub 2), N(sub 2), SO(sub 2), and other important planetary gases.Voyager and International Ultraviolet Explorer (IUE) spacecraft have established that band systems of H(sub 2) and N(sub 2) are the dominant UV molecular emissions in the solar system produced by electron impact. Applications of our data to models of Voyager, IUE, Galileo, and Hubble Space Telescope observations of the planets will be described.

molecular emissions↗
NASA NTRS1981

Vacuum UV and soft X-ray optical emissions from electron impact on metals

Spectrograms from 2200 to 20 A of optical emissions produced by a simple lamp using fast (3-10-keV) electron impact on tungsten and tantalum targets are presented. The lamp dissipated up to 5 kW/sq cm on the target surface, simultaneously cleaning the surface and generating bremsstrahlung in the soft X-ray region with 3-keV electron impact and longer wavelength transition radiation at the higher energy. In both the bremsstrahlung and transition radiation modes, the lamp emissions were of sufficient strength and reproducibility to qualify the two mechanisms as potential processes for use in a secondary standard light source. Calculated spectral distributions of transition radiation for normally incident electrons on tungsten, tantalum, and aluminum targets, with a viewing direction 45 deg from the normal, are also shown.

Hughes, R. H.↗
DOE OSTI2024

Modelling of the electron cyclotron emission burst from a laboratory tokamak plasma with loss-cone maser instability

The maser instability associated with the loss-cone distribution has been widely invoked to explain the radio bursts observed in the astrophysical plasma environment, such as aurora and corona. In the laboratory plasma of a tokamak, events reminiscent of these radio bursts have also been frequently observed as an electron cyclotron emission (ECE) burst in the microwave range (~2f ce near the last closed flux surface) during transient magnetohydrodynamic events. These bursts have a short duration of ~10 μs and display a radiation spectrum corresponding to a radiation temperature T e,rad of over 30 keV while the edge thermal electron temperature T e is only in the range of 1 keV. Suprathermal electrons can be generated through magnetic reconnection, and a loss-cone distribution can be generated through open stochastic field lines in the magnetic mirror of the near-edge region of a tokamak plasma. Radiation modelling shows that a sharp distribution gradient ∂f/∂v ⊥ > 0 at the loss-cone boundary can cause a negative absorption of ECE radiation through the maser instability. The negative absorption then amplifies the radiation so that the microwave intensity is significantly stronger than the thermal value. The significant T e,rad from the simulations suggests the potential role of the loss-cone maser instability in generating the ECE burst in a tokamak.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗