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Results for “electron cyclotron emission”

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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

On the role of the energy of suprathermal electrons in the generation of auroral kilometric radiation

The relativistic dispersion equation based on the cyclotron maser theory for a DGH energetic electron distribution is examined in order to identify and understand the physical conditions under which fundamental O mode and second harmonic X mode radiations can dominate over fundamental X mode emission in low density auroral kilometric radiation source regions. It is found that the energy of the auroral electrons can play a significant role in determining the dominant wave mode. The temporal and spatial growth rates of both the fundamental O mode as well as the second harmonic X mode remain high for energies as low as several hundred eV of the suprathermal electrons, while the fundamental X mode is suppressed for energies no higher than approximately 1 keV due to its relativistic resonance condition.

Wong, H. K.↗
NASA NTRS1991

Simultaneous Solar Maximum Mission (SMM) and Very Large Array (VLA) observations of solar active regions

Very Large Array observations at 20 cm wavelength can detect the hot coronal plasma previously observed at soft x ray wavelengths. Thermal cyclotron line emission was detected at the apex of coronal loops where the magnetic field strength is relatively constant. Detailed comparison of simultaneous Solar Maximum Mission (SMM) Satellite and VLA data indicate that physical parameters such as electron temperature, electron density, and magnetic field strength can be obtained, but that some coronal loops remain invisible in either spectral domain. The unprecedent spatial resolution of the VLA at 20 cm wavelength showed that the precursor, impulsive, and post-flare components of solar bursts originate in nearby, but separate loops or systems of loops.. In some cases preburst heating and magnetic changes are observed from loops tens of minutes prior to the impulsive phase. Comparisons with soft x ray images and spectra and with hard x ray data specify the magnetic field strength and emission mechanism of flaring coronal loops. At the longer 91 cm wavelength, the VLA detected extensive emission interpreted as a hot 10(exp 5) K interface between cool, dense H alpha filaments and the surrounding hotter, rarefield corona. Observations at 91 cm also provide evidence for time-correlated bursts in active regions on opposite sides of the solar equator; they are attributed to flare triggering by relativistic particles that move along large-scale, otherwise-invisible, magnetic conduits that link active regions in opposite hemispheres of the Sun.

Willson, Robert F.↗
NASA NTRS1987

Low-altitude ISIS 1 observations of auroral radio emissions and their significance to the cyclotron maser instability

Low-altitude ISIS 1 observations are presented which support the cyclotron maser instability as the generation mechanism of most, but not all, auroral radio emissions. The observations confirm the ability of the mechanism to generate different wave modes and harmonics as the ratio of the plasma frequency to gyrofrequency f(N)/f(H) increases depending on the form of the energetic electron distribution function. The present observations correspond to conditions where f(N)/F(H) is always larger than 0.2 and is typically about 1.0. The observations and instability growth rate calculations indicate that second harmonic radiation in the extraordinary and the Z modes is directly generated at low altitudes. By far the most common signals observed near ISIS 1 perigee, however, are in the fundamental Z and whistler modes. The observations and calculations in the case of the Z mode suggest that the pertinent process involves a maser that does not saturate, i.e., that group velocity effects are important. The whistler mode is the most intense signal observed at low altitudes. Since the cyclotron maser generated whistler mode waves have peak growth rates for downward field-aligned propagation, they should be able to penetrate the ionosphere. This process may provide the explanation of occasional reports, dating back to the International Geophysical Year time period, of ground level detection of radio noise associated with the aurora.

Benson, Robert 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.↗
DOE OSTI2021

Observation of second harmonic electron cyclotron resonance heating and current-drive transition during non-inductive plasma start-up experiment in QUEST

Here, noninductive plasma current start-up using 2nd harmonic electron cyclotron resonance heating (ECRH) with oblique radio frequency (RF) injection is demonstrated in a Q-shu University experiment with steady-state spherical tokamak. A strong transition was observed in the heating and plasma current ramp-up. The initial bulk electron heating regime exhibits T ebulk ~ 140 eV and no hard x-ray (HXR) emission with a low I p of ~15 kA; it abruptly transitions to a regime that exhibits a low T ebulk of ~10 eV and a strong HXR emission with a high I p of ~50 kA. This behavior is distinctly different from that observed in previous fundamental ECRH experiments. The mechanism of the heating and current drive transition are investigated considering wave power absorption and plasma power balance. The results indicate that the transition is caused by the favorable heating of tail electrons where the RF power absorption at the 2nd harmonic increases nearly linearly with T etail , while the power transfer from the tail electrons to the bulk electrons decreases with 1/T etail 0.5 . This causes a rapid transition to a state with high T etail while reducing T ebulk towards colder ion temperature. The understanding of the transition mechanism helps to consider plasma current start-up using 2nd harmonic ECRH for tokamak reactors such as JT-60 SA and ITER.

QUEST↗
NASA NTRS1983

X-ray emission from cataclysmic variables

X-ray observations of cataclysmic variables and theoretical work on X-ray emission from them are reviewed, emphasizing recent developments. Observations of luminosities and space densities, X-ray spectra and temporal behavior, and X-ray emitting cataclysmic variables in globular clusters are addressed. The relationship of disk and radial accretion to X-ray emission is qualitatively considered, and the spectra and correlation between spectral temperature and luminosity are examined for magnetic and nonmagnetic stars. The relationship between ionization structure and line features is summarized, and nuclear burning and electron conduction are briefly addressed. Important issues concerning X-ray emission from cataclysmic variables are discussed, including magnetic fields, the origin of hard and soft X-rays, the soft X-ray puzzle in AM Her stars, nuclear burning, long-period pulsing sources, cyclotron-dominated sources, high-luminosity sources, and the stability of accretion flow.

Lamb, D. Q.↗
DOE OSTI2022

Verification of a fully kinetic ion model for electromagnetic simulations of high-frequency waves in toroidal geometry

For the research of high-frequency electromagnetic waves in tokamaks, an electromagnetic simulation model, in which the ion dynamics is described by a six-dimensional Vlasov equation and the electron dynamics is described by a drift kinetic equation, is formulated and implemented in the global gyrokinetic toroidal code (GTC). Analytic dispersion relations are derived in reduced systems and compared with various theories to verify the model. Linear simulations of a generalized ion Bernstein wave and ion cyclotron emission are verified by comparing the GTC simulation results with analytic dispersion relation theory and magnetoacoustic cyclotron instability theory, respectively, in cylindrical geometry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1990

Acceleration of runaway electrons in solar flares

The dc electric field acceleration of electrons out of a thermal plasma and the evolution of the runaway tail are studied numerically, using a relativistic quasi-linear code based on the Ritz-Galerkin method and finite elements. A small field-aligned electric field is turned on at a certain time. The resulting distribution function from the runaway process is used to calculate the synchrotron emission during the evolution of the runaway tail. It is found that, during the runaway tail formation, which lasts a few tens of seconds for typical solar flare conditions, the synchrotron emission level is low, almost ot the same order as the emission from the thermal plasma, at the high-frequency end of the spectrum. However, the emission is enhanced explosively in a few microseconds by several orders of magnitude at the time the runaway tail stops growing along the magnetic field and tends toward isotropy due to the pitch-angle scattering of the fast particles. Results indicate that, in order to account for the observed synchrotron emission spectrum of a typical solar flare, the electric field acceleration phase must be accompanied or preceded by a heating phase which yields an enhanced electron temperature of about 2-15 keV in the flare region if the electric field is 0.1-0.2 times the Dreicer field and cyclotron-to-plasma frequency ratios are of order 1-2.

Moghaddam-Taaheri, E.↗
NASA NTRS1983

Radio emission from AM Herculis - The quiescent component and an outburst

The VLA has been used to search for radio emission from the AM Her-type binaries VV Pup, EF Eri, PG 1550 + 191, CW 1103 + 354, and AN UMa, at 4.9 GHz. A remarkable 10-min outburst was detected from AM Her at 4.9 GHz, which was about 20 times more intense than the quiescent emission and was essentially 100 percent circularly polarized. It is suggested that the quiescent emission of AM Her can be accounted for by 500-keV electrons trapped in the magnetosphere of the white dwarf, provided that the electron energy spectrum is quite hard and that the spectral hardness or number density of energetic electrons increases with radius, while the outburst is probably due to an electron-cyclotron maser operating near the surface of the red dwarf companion. The implied existence of a 1000-gauss localized magnetic field and a corona on the red dwarf has consequences for mass transfer, field line interactions, and variable activity.

Dulk, G. A.↗
NASA NTRS1990

Electron beam injection during active experiments. I - Electromagnetic wave emissions

The wave emissions produced in Echo 7 experiment by active injections of electron beams were investigated to determine the properties of the electromagnetic and electrostatic fields for both the field-aligned and cross-field injection in such experiments and to evaluate the sources of free energy and relative efficiencies for the generation of the VLF and HF emissions. It is shown that, for typical beam energies in active experiments, electromagnetic effects do not substantially change the bulk properties of the beam, spacecraft charging, and plasma particle acceleration. Through simulations, beam-generated whistlers; fundamental z-mode and harmonic x-mode radiation; and electrostatic electron-cyclotron, upper-hybrid, Langmuir, and lower-hybrid waves were identified. The characteristics of the observed wave spectra were found to be sensitive to both the ratio of the electron plasma frequency to the cyclotron frequency and the angle of injection relative to the magnetic field.

Winglee, R. M.↗
NASA NTRS1985

Plasma waves and instabilities

An account is given of the waves and instabilities occurring at collisionless shocks, with attention to the mechanisms responsible for the generation of these waves. The transition region of the shock usually involves an abrupt broadband burst of electrostatic noise that extends from below the lower hybrid resonance to near the electron plasma frequency, and by a broadband burst of whistler mode EM noise below the electron cyclotron frequency. Electrostatic lower hybrid waves are also noted. Upstream of the shock, electron plasma oscillations, ion acoustic waves, and intense ULF MHD waves are often observed. The region downstream of the shock is usually very chaotic; electrostatic waves often extend long distances into the downstream region, together with whistler mode emissions.

Gurnett, Donald A.↗
NASA NTRS1993

On the generation of plasma waves in Saturn's inner magnetosphere

Voyager 1 plasma wave measurements of Saturn's inner magnetosphere are reviewed with regard to interpretative aspects of the wave spectrum. A comparison of the wave emission profile with the electron plasma frequency obtained from in situ measurements of the thermal ion density shows good agreement with various features in the wave data identified as electrostatic modes and electromagnetic radio waves. Theoretical calculations of the critical flux of superthermal electrons able to generate whistler-mode waves and electrostatic electron cyclotron harmonic waves through a loss-cone instability are presented. The comparison of model results with electron measurements shows excellent agreement, thereby lending support to the conclusion that a moderate perpendicular anisotropy in the hot electron distribution is present in the equatorial region of L = 5-8.

Barbosa, D. D.↗
DOE OSTI2024

Toroidal injection angle dependence of EC assisted plasma initiation at DIII-D

An experimental scan of the electron cyclotron waves (EC) toroidal injection angle in plasma breakdown is performed at the DIII-D tokamak. The second harmonic, extraordinary mode EC is used for the study. The dependence of n e and T e on the EC injection angle cannot be conclusively drawn from this study due to the large error bars in the n e and T e measurements. On the other hand, high T e data points are observed in some discharges which can be explained by nonlinear heating. The D α emission measurement shows a clear relation between the breakdown time and the injection angle. An experimental investigation of the cause of the dependence of breakdown delay on the EC injection angle suggests that when the injection angle is oblique, the EC heating after the reflection at the inboard wall may become ineffective and cause the breakdown delay even when the EC heating before and directly upon injection remains effective. A preliminary run of the heat and transport balance code DYON indicates that the obtained dataset is suitable for a quantitative validation of EC absorption models.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1986

The electron-cyclotron maser instability as the source of solar type V continuum

In this paper, it is proposed that the electron-cyclotron (EC) maser instability can be the source of solar type V bursts. The propagation of electrons up an open field line is examined, and it is shown that the resultant distribution can be subject to the bump-in-tail (BIT) or the EC maser instabilities, or both. The characteristics of the emission from the BIT and EC maser instabilities when they are driven by such distributions are compared. It is proposed that type V bursts are produced by the coalescence of the upper hybrid waves produced by the maser instability, while type IIIs are produced by the BIT instability.

Winglee, R. M.↗
NASA NTRS1981

The generation mechanism for magnetosheath lion roars

The origin of lion roars, intense electromagnetic whistler-mode waves which occur throughout the magnetosheath, is investigated based on particle and field data obtained on the ISEE satellites. Analysis of the measured magnetic fields, plasma densities and plasma wave intensities during periods of lion roar emission reveals the lion roar bursts to be correlated with decreases in magnetic field intensity, while the plasma density exhibits a strong anticorrelation with the magnetic field variability during the bursts and the total plasma pressure remains essentially constant. Results indicate that the waves can originate by the cyclotron resonant instability with anisotropic magnetosheath electrons whenever the magnetic energy per particle falls to values comparable with the electron thermal energy. Variations in the magnetic energy appear to be associated with the hydromagnetic mirror instability which in turn is excited by a pressure anisotropy in the magnetosheath ion population.

Thorne, R. M.↗
NASA NTRS1989

Electron cyclotron resonance deposition of a-Si:H and a-C:H films

Amorphous silicon (a-Si:H) and amorphous carbon (a-C:H) films have been deposited by electron cyclotron resonance (ECR) microwave plasma enhanced CVD. A high deposition rate of 25 A/sec and a light-to-dark conductivity ratio of 500,000 for a-Si:H films have been achieved by the ECR process using a pure silane plasma. ECR microwave plasmas have been analyzed by in situ optical emission spectroscopy (OES) and have shown a strong H-asterisk emission at 434 nm indicating higher chemical reactivity than RF plasmas. The linear correlation between the film deposition rate and the SiH-asterisk emission intensity of ECR silane plasma suggests that SiH-asterisk species are related to the neutral radicals which are responsible for the a-Si:H film deposition. Hard and soft a-C:H films have been deposited by ECR with and without RF bias power, respectively. The RF bias to the substrate is found to play a critical role in determining the film structure and the carbon bonding configuration of ECR deposited a-C:H films. Raman spectra of these films indicate that ECR deposition conditions can be optimized to produce diamond films.

Shing, Y. H.↗
NASA NTRS1996

Plasma Heating and Flow in an Auroral Arc

We report direct observations of the three-dimensional velocity distribution of selected topside ionospheric ion species in an auroral context between 500 and 550 km altitude. We find heating transverse to the local magnetic field in the core plasma, with significant heating of 0(+), He(+), and H(+), as well as tail heating events that occur independently of the core heating. The 0(+) velocity distribution departs from bi-Maxwellian, at one point exhibiting an apparent ring-like shape. However, these observations are shown to be aliased within the auroral arc by temporal variations that arc not well-resolved by the core plasma instrument. The dc electric field measurements reveal superthermal plasma drifts that are consistent with passage of the payload through a series of vortex structures or a larger scale circularly polarized hydromagnetic wave structure within the auroral arc. The dc electric field also shows that impulsive solitary structures, with a frequency spectrum in the ion cyclotron frequency range, occur in close correlation with the tail heating events. The drift and core heating observations lend support to the idea that core ion heating is driven at low altitudes by rapid convective motions imposed by the magnetosphere. Plasma wave emissions at ion frequencies and parallel heating of the low-energy electron plasma are observed in conjunction with this auroral form; however, the conditions are much more complex than those typically invoked in previous theoretical treatments of superthermal frictional heating. The observed ion heating within the arc clearly exceeds that expected from frictional heating for the light ion species H(+) and He(+), and the core distributions also contain hot transverse tails, indicating an anomalous transverse heat source.

Moore, T. E.↗
NASA NTRS1978

Consequences of narrow cyclotron emission from Hercules X-1

Explanations of the line feature in the hard X-ray (58 keV) spectrum of the compact X-ray source Hercules X-1 are presented. The most important characteristic of the emission (interpreted as a cyclotron emission from a strong magnetic field, i.e., B greater than one trillion Gauss) is that the FWHM is less than 12 keV, with a total observed luminosity in the line of approximately 1% of the total X-ray luminosity. If the source region is only at the magnetic poles of a neutron star, the electrons are confined to a path nearly parallel to the B-field lines, and the angle of emission will be narrow. Photon emission under such circumstances is also discussed; and it is suggested that photons can leave either through holes in the shell formed by the hard X-rays, or can escape through the shell itself. Attention is given to the accretion flow structure near the magnetopause, as a critical parameter of narrow line emission.

Weaver, R. P.↗