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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Laboratory observations of RF emission at plasma electron frequency and n + 1/2 times the electron cyclotron frequency in electron beam-plasma and beam-beam interactions

Electric field emissions at frequencies of (n + 1/2) times the electron cyclotron frequency have been generated in a large-scale electron beam experiment in a vacuum facility. These emissions arise when a contrastreaming beam configuration exists, the primary beam consisting of monoenergetic electrons (50 eV to 5 keV) and the other beam of lower-energy backscattered secondary electrons. It is suggested that the same mechanism could also be the source of the observed 3/2 times the electron cyclotron frequency emissions at auroral latitudes. In the absence of the beam-beam instability, weak oscillations were observed at the plasma frequency. In the latter case no significant modifications of the primary beam velocity distribution occurred, and the beam configuration is adequately described by single-particle motion in the ambient magnetic field.

Bernstein, W.↗
NASA NTRS1994

Electron cyclotron wave generation by relativistic electrons

We show that an energetic electron distribution which has a temperature anisotropy (T perpendicular to b is greater than T parallel to b), or which is gyrating about a DC magnetic field, can generate electron cyclotron waves with frequencies below the electron cyclotron frequency. Relativistic effects are included in solving the dispersion equation and are shown to be quantitatively important. The basic idea of the mechanism is the coupling of the beam mode to slow waves. The unstable electron cyclotron waves are predominantly electromagnetic and right-hand polarized. For a low-density plasma in which the electron plasma frequency is less than the electron cyclotron frequency, the excited waves can have frequencies above or below the electron plasma frequency, depending upon the parameters of the energetic electron distribution. This instability may account for observed Z mode waves in the polar magnetosphere of the Earth and other planets.

Wong, H. K.↗
NASA NTRS2017

A First-Principles Model Based on Saturation of the Electron Cyclotron Drift Instability for Electron Transport in Hydrodynamics Simulations of Hall Thruster Plasmas

We present a computational model based on the hypothesis that the higher-than-expected electron mobility across magnetic field lines observed in Hall thrusters is due to the growth and eventual saturation of the electron cyclotron drift instability. The key improvement of this model with respect to previous work is that it decouples the saturation of the instability from the correlation that exists between mobility and magnitude of the wave perturbations in linear theory, thereby enabling first-principles simulations. The model has been incorporated in the 2-D (r-z) multi-fluids code Hall2De and simulations of the H6 thruster at 300 V, 20 A are numerically stable and achieve a steady-state solution at a computational cost that is not significantly higher than previous Hall2De simulations. The computed location of the acceleration region is found to be within 10% of the length of the acceleration channel compared to that inferred by experiments. The simulations also capture well the plasma gradients along the channel centerline of this thruster. To further establish the validity of this model, we plan to conduct simulations of other thrusters and/or operating conditions.

Lopez Ortega, Alejandro↗
NASA NTRS1985

Electron-cyclotron maser instability caused by hot electrons

The electron-cyclotron maser instability is studied for energetic electrons with a loss-cone distribution. The instability can occur at all angles of propagation for a wide range of parameters. The growth rate is significantly reduced by the presence of a population of cold electrons, and the instability can be suppressed if the density of the cold electrons is sufficiently large and the temperature of the energetic electrons is not too high.

Wong, H. K.↗
NASA NTRS1991

Simultaneous excitation of broadband electrostatic noise and electron cyclotron waves in the plasma sheet

Electron cyclotron harmonics and broadband electrostatic noise (BEN) are often observed in the earth's outer plasma sheet. While it is well known that ion beams in the plasma sheet boundary layer can generate BEN, new two-dimensional electrostatic simulations show that field-aligned ion beams with a small perpendicular ring distribution can drive not only BEN, but also electron cyclotron harmonic (ECH) waves simultaneously. Simulation results are presented here using detailed diagnostics of wave properties, including dispersion relations of all wave modes.

Berchem, Jean P.↗
NASA NTRS1984

Electron-cyclotron maser emission - Relative growth and damping rates for different modes and harmonics

The temporal growth rate and the number of e-folding growths are calculated and compared for the following wave modes due to a loss-cone-driven cyclotron maser: fundamental x, o, and z modes and second harmonic x and o modes. The dominant mode of the maser should be the fastest growing mode for a saturated maser and should be the mode with the greatest number of e-folding growths for an unsaturated maser; this mode is the fundamental x mode) for a plasma frequency to cyclotron frequency ratio of less than about 0.3; it is the z mode (or perhaps the fundamental o mode) for ratios between 0.3 and 1.0, and the z mode (or perhaps the second harmonic x mode) for ratios between 1.0 and 1.3. Two main points are made: the dominance of the z mode over the range of ratios considered and the very weak effect of cyclotron damping. Electron-cyclotron maser emission is seen as responsible for auroral kilometric radiation, decametric radio emission from Jupiter and Saturn, solar microwave spike bursts, and microwave emission from some flare stars.

Melrose, D. B.↗
NASA NTRS1984

Parametric instabilities during electron cyclotron heating of tandem mirrors

Electron cyclotron resonance heating is one of the most commonly used methods of heating electrons in the plugs and in the thermal barriers of tandem mirrors. The intense coherent electromagnetic waves used for such heating are susceptible to parametric decay into other modes. Significant growth rates are found for the decay of either ordinary or extraordinary waves into two magnetized electron plasma waves. This and related effects may result in electron heating mechanisms rather different than those assumed in linear ray-tracing calculations. These results may help explain the unusual effects observed during heating of the Phaedrus tandem mirror device. In the general case, these instabilities may be strongly inhibited by density gradients.

Nicholson, D. R.↗
DOE OSTI2026

Electromagnetic Analysis of ITER Electron Cyclotron Emission Model

The ITER electron cyclotron emission (ECE) diagnostic system is located at diagnostics shielding module 2 (DSM2), equatorial port 9 (EP9), to measure electron temperature profile and electron temperature fluctuations, and also assess nonthermal electron distributions via the oblique view. Therefore, ECE has both radial and oblique views with two hot sources for calibration and two couples of mirrors for two different optical views. It shall receive that the large electromagnetic (EM) loads up to 100-MN/m3 force density due to the eddy currents on the copper mirrors generated by the short transient plasma disruption. The simplified EM analysis model using magnetic field ( B ) data and flux variations (dB/dt) method based on the worst case of plasma disruption, MD_DW_EXP16MS_CATIII, has been developed to calculate the force and moments for each ECE component and support structure for EP9 DSM2 Bay2 and Bay3. The B and dB/dt methods use the constant B and dB/dt assumed for each local bay space, but the real B and dB/dt are basically varied along the radial direction of each bay. The complex global model with the local ECE components and support structure using Maxwell transient has been developed to do EM analysis to compare the results of the B and dB/dt models. The volumetric EM force density of the whole ECE components and support structure can be used for the subsequent structural analysis. In conclusion, combined with the thermal and nuclear loads and seismic and initial loads, the ECE integration analysis can be finalized for the operation case.

Fang, J. [Princeton Plasma Physics Laboratory (PPP↗
NASA NTRS1987

Evolution of the axial electron cyclotron maser instability, with applications to solar microwave spikes

The nonlinear evolution of cyclotron radiation from streaming and gyrating electrons in an external magnetic field is analyzed. The nonlinear dynamics of both the fields and the particles are treated fully relativistically and self-consistently. The model includes a background plasma and electrostatic effects. The analytical and numerical results show that a substantial portion of the beam particle energy can be converted to electromagnetic wave energy at frequencies far above the electron cyclotron frequency. In general, the excited radiation can propagate parallel to the magnetic field and, hence, escape gyrothermal absorption at higher cyclotron harmonics. The high-frequency Doppler-shifted cyclotron instability can have saturation efficiencies far higher than those associated with well-known instabilities of the electron cyclotron maser type. Although the analysis is general, the possibility of using this model to explain the intense radio emission observed from the sun is explored in detail.

Vlahos, Loukas↗
DOE OSTI2025

Electromagnetic Analysis of ITER Electron Cyclotron Emission Components and Support Structures for the Preliminary Design Review

The ITER electron cyclotron emission (ECE) diagnostic system is located at Design Shield Module (DSM) 2, Equatorial Port (EP) 9 to measure electron temperature profile and electron temperature fluctuations and also to assess nonthermal electron distributions via the oblique view. Therefore, ECE has both radial and oblique views with two couples of mirrors for two different optical views. This ECE diagnostic system shall be exposed to significant power due to unabsorbed electron cyclotron heating power in the plasma. It shall also receive large electromagnetic (EM) loads up to 100 MN/m 3 force density due to the eddy currents generated by the short 16-ms transient plasma disruption. The global EM models of EP12 and EP11 with the worst case of plasma disruption Major Disruption Downward Exponential 16 ms Category III (MD_DW_EXP16MS_CATIII) have been provided by ITER. However, the support structure for these critical components, including four mirrors, is still under the design and development phase, especially during the period of preliminary design reviews (PDRs). For those small in-vessel components that are not modeled explicitly for the PDRs, we can extract the magnetic field (B) data and flux variations (dB/dt) at those locations from the global model and then use the B and dB/dt method to calculate the eddy currents, EM forces, and torques on those components in the local submodels. In conclusion, this paper will present the detailed PDR EM analysis results of the ECE components and support structures.

Electromagnetic↗
NASA NTRS1983

An electron cyclotron maser instability for astrophysical plasmas

The electron cyclotron maser instability is analyzed for a plasma which consists of a suprathermal electron component characterized by velocity-space anisotropies in directions both parallel and perpendicular to the ambient magnetic field, as well as a high-density thermal plasma in which omega sub e is approximately equal to Omega sub e (where omega sub e and Omega sub e are the electron plasma and cyclotron frequencies). The complete relativistic resonance condition is used and shown to result in a 'resonance ellipse' in momentum space. The instability is considered for both cold and warm suprathermal electron distributions, and for frequencies omega approximately equal to Omega sub e in the ordinary mode and omega approximately equal to 2(Omega sub e) in the fast extraordinary mode. It is shown that the growth rates are comparable for these harmonics over a wide range of parameters which, since they are escape modes of the plasma, can lead to comparable radiation intensities.

Freund, H. P.↗
NASA NTRS1985

Fundamental and harmonic electron cyclotron maser emission

The plasma conditions and features of the energetic electron distribution in electron cyclotron maser emission for which growth in a particular mode is favored when the ratio of the plasma frequency omega(p) to the electron cyclotron frequency Omega(e) is greater than about 0.3 are determined. It is shown that growth at the fundamental is suppressed as omega(p)/Omega(e) increases and emission at harmonics of Omega(e) dominates. Growth at harmonics of Omega(e) is not restricted to the O and X modes, but can also occur for the Z mode. Whether or not growth in a particular mode dominates depends both on omega(p)/Omega(e) and on the form of the distribution. If the density of the energetic electrons is sufficiently large, the dispersion relations of the O and X modes are modified so that the group velocities of the growing O and X mode waves can be comparable to that of the growing Z mode waves.

Winglee, R. M.↗
NASA NTRS1986

Electron-cyclotron maser emission during flares: Emission in various modes and temporal variations

Absorption of radiation at the electron-cyclotron frequency, OMEGA sub e, generated by the electron-cyclotron maser instability was proposed as a possible mechanism for transporting energy and heating of the corona during flares. Radiation from the same instability but at harmonics of OMEGA sub e is believed to be the source of solar microwave spike bursts. The actual mode and frequency of the dominant emission from the maser instability is shown to be dependent on: (1) the plasma temperature, (2) the form of the energetic electron distribution, and (3) on the ratio of the plasma frequency omega sub p to OMEGA sub e. As a result, the emission along a flux tube can vary, with emission at harmonics being favored in regions where omega sub p/OMEGA sub e approx. equal to or greater than 1. Changes in the plasma density and temperature in the source region associated with the flare can also cause the characteristics of the emission to change in time.

Winglee, R. M.↗
DOE OSTI2025

Electron cyclotron emission measurements and modeling in optically semi-transparent plasma on the HSX stellarator

On the Helically Symmetric Experiment (HSX), electron cyclotron emission (ECE) at the second harmonic of the electron gyrofrequency is measured with a 16-channel heterodyne receiver. An ECE radiometer diagnostic has been calibrated with a broadband frequency source, allowing independent measurements of the electron temperature. The antenna pattern has a significant impact on the measurements, and modeling its effect is necessary to produce an ECE radiation temperature spectrum. Measurements, calibration results, and modeling of the ECE data are presented in this paper. At a relatively high plasma density, HSX plasmas are thermal, and the radiation temperature measured by the radiometer is in good agreement with the electron temperature measured by a Thomson scattering diagnostic. At a relatively low plasma density, the deviation from a Maxwellian distribution is large, and asymmetry in the radiation temperature profile is measured. These measurements are supported by single-pass and multi-pass ray tracing calculations of the electron cyclotron emission using the TRAVIS ray tracing code. Thermal and nonthermal electron populations exist in HSX, and the effect of these populations on the asymmetry in the measured emission is presented.

Cyclotron radiation↗
NASA NTRS1982

The importance of plasma effects on electron-cyclotron maser-emission from flaring loops

Electron cyclotron maser instability has been suggested as the cause of the observed short (10-20 msec), intense (an approximate brightness temperature of 10 to the 15th K) and up to 100% polarized microwave solar emission. It is shown that plasma effects and thermal cyclotron damping, ignored in previous theories, play an important role in controlling the frequency range of the emission. The radio emission is suppressed for ratios of the plasma frequency to the cyclotron frequency smaller than 0.4. An examination of the cyclotron damping, reveals that the maser action is suppressed unless a large fraction (i.e., over 10%) of the accelerated electrons participates in the emission process.

Sharma, R. R.↗
NASA NTRS1982

Electron-cyclotron masers as the source of certain solar and stellar radio bursts

The theory of electron-cyclotron masers as they might apply in the astrophysical context is developed, and it is suggested that such masers provide an explanation for the very bright emission known to be associated with certain kinds of radio bursts observed on the Sun and other stars. Some of the observed properties of solar and stellar radio bursts that seem to require amplification of the radiation are summarized, including millisecond solar spikes, RS CVn binaries, and flares on M dwarf stars. Recent developments in the theory of electron-cyclotron masers are summarized and the current theory is applied to electrons with a loss cone anisotropy, estimating the growth rate and saturation levels. In the interpretation of solar microwave spikes and RS CVn binaries, the mechanisms of gyromagnetic absorption, maser at the second harmonic, polarization, and angular distribution are examined in the light of the theory.

Melrose, D. B.↗
NASA NTRS1984

Electron-cyclotron maser radiation from a relativistic loss-cone distribution

A relativistic analysis of the electron-cyclotron maser instability in a loss-cone distribution is presented, extending the treatment of Lau and Chu (1983) to include the effects of finite k-perpendicular (as encountered in laboratory tandem-mirror devices with mean energies in excess of 50 keV). The results are presented in graphs, and it is found that the k-perpendicular effects are significant, so that emission perpendicular to the magnetic field is associated with most rapid growth of the instability. The persistence of the instability when the ratio of the plasma frequency to the electron-cyclotron frequency is less than 0.1 is demonstrated, and the factors which need to be accounted for in applying the results to actual mirror devices are indicated.

Pritchett, P. L.↗