Spontaneous radiofrequency emission from hot-electron plasmas
Spontaneous radio frequency emission from hot electron plasma, and enhanced cyclotron radiation from electron cyclotron resonance discharge
HOT ELECTRON↗
SEARCH · Engineering Papers
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Flare stars and solar bursts - High resolution in time and frequency
Coronal loops on the sun and nearby stars are studied using observations at 20-cm wavelength with high resolution in time and frequency. Observations of the dwarf M star AD Leonis with high time resolution led to the discovery of a quasi-periodic train of circularly polarized spikes with a mean periodicity of 32 + or - 5 ms and a total duration of 150 ms. Observations at closely spaced wavelengths using the VLA revealed a narrow-band structure in solar bursts and in the slowly varying radiation of the dwarf M star YZ Canis Minoris. This narrow-band emission may be attributed to electron-cyclotron maser radiation. Maser action at the second or first harmonic of the gyrofrequency implies magnetic field strengths of 250 and 500 G, respectively. Hence, observations with high resolution in time and frequency suggest coherent processs in the coronas of the sun and dwarf M stars. It is noted that the scientific potential suggested by the present data can be realized by the development of a solar-stellar synthesis radiotelescope. This instrument would be dedicated to solar and stellar observations with high angular, temporal, and frequency resolution.
Lang, K. R.↗
The electron-cyclotron maser instability as a source of plasma radiation
The generation of continuum bursts from the sun at dm and m wavelengths (in particular, type IV bursts) via the electron-cyclotron-maser instability is examined. The maser instability can be driven by an electron distribution with either a loss-cone anisotropy or a peak at large pitch angles. For omega(p)/Omega(e) much greater than 1, the maser emission is produced by electrons interacting through a harmonic (cyclotron) resonance and is electrostatic, being in the upper hybrid mode at frequencies approximately equal to omega(p). Coalescence processes are required to convert the electrostatic waves into transverse radiation which can escape from the source region. Whether the resultant spectrum is nearly a smooth continuum or has a zebra-stripe pattern (both of which occur in type IV bursts) depends on the form of the electron distribution, inhomogeneities in the density and magnetic field, and whether the maser reaches saturation. For at least the case of some type IV dm bursts with fine structure, comparison with observations seems to indicate that the electrons producing the emission are more likely to have a loss-cone distribution, and that the maser instability is not at saturation.
Winglee, R. M.↗
X-ray Emission from Magnetized Neutron Star Atmospheres at Low Mass Accretion Rates
Recent observations of X-ray pulsars at low luminosities allow, for the first time, to compare theoretical models for the emission from highly magnetized neutron star atmospheres at low mass accretion rates ( M ≲ 10(exp 15) g s(exp -1)) with the broadband X-ray data. The purpose of this paper is to investigate the spectral formation in the neutron star atmosphere at low M and to conduct a parameter study of physical properties of the emitting region. We obtain the structure of the static atmosphere, assuming that Coulomb collisions are the dominant deceleration process. The upper part of the atmosphere is strongly heated by the braking plasma, reaching temperatures of 30–40 keV, while its denser isothermal interior is much cooler (~2 keV). We numerically solve the polarized radiative transfer in the atmosphere with magnetic Compton scattering, free-free processes, and non-thermal cyclotron emission due to possible collisional excitations of electrons. The strongly polarized emitted spectrum has a double-hump shape that is observed in low-luminosity X-ray pulsars. A low-energy “thermal” component is dominated by extraordinary photons that can leave the atmosphere from deeper layers due to their long mean free path at soft energies. We find that a high-energy component is formed due to resonant Comptonization in the heated non-isothermal part of the atmosphere even in the absence of collisional excitations. The latter, however, affect the ratio of the two components. A strong cyclotron line originates from the optically thin, uppermost zone. A fit of the model to NuSTAR and Swift/XRT observations of GX3041 provides an accurate description of the data with reasonable parameters. The model can thus reproduce the characteristic double-hump spectrum observed in low-luminosity X-ray pulsars and provides insights into spectral formation.
X-Ray binaries↗
Prototype X-ray and Gamma Detection with Cyclotron Radiation Emission Spectroscopy
Cyclotron radiation emission spectroscopy, or CRES, is a novel approach to measuring the energy of an electron. By trapping a free electron in a high magnetic field, it undergoes cyclotron motion and emits radiofrequency (RF) waves. The frequency of this RF radiation is directly related to the energy of the electron. Because many cycles of the RF emission are recorded, the energy resolution of the CRES system is on the order of a single electron volt. To make a CRES system sensitive to photons, a target gas is used to induce a photoelectric effect, producing the electron that is subsequently trapped. By adding the binding energy of the target atom, the energy of the incident photon may be reconstructed. Using a xenon target gas, photoelectric interactions dominate up to approximately 300 keV, covering not only all atomic shell X-rays of the elements, but many low-lying nuclear states as well, including key transuranic elements related to nuclear security. CRES holds the potential of maintaining single-eV resolution up to this 300-keV range, thereby surpassing current state-of-the-art detectors by a factor of 10-100. The instrumental resolution of the system is limited by the uniformity of the applied magnetic field.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Further studies of auroral roar
Extended observations of auroral roar, a weak radio emission near the second harmonic of the electron cyclotron frequency, are reported. A total of 69 events were recorded and analyzed. Data for frequency band, duration, and local time of occurrence are presented. The height of the generation region is estimated to be 275-575 km.
Kellogg, P. J.↗
Relativistic dispersion and the generation of auroral kilometric radiation
Under the conditions at which auroral kilometric radiation (AKR) is known to be produced by a plasma sheet electron region, relativistic effects of the dispersion of extraordinary-mode waves near the electron cyclotron frequency are found to be very significant. The application of linear theory and computer simulation to a model distribution indicates that an extraordinary mode of a particular Reynolds number dominated the radiation emission due to the cyclotron maser instability, suggesting that hot electrons determine the propagation characteristics of AKR and that larger growth rates are possible for direct amplification of extraordinary waves in the auroral region than had been predicted by calculations employing cold plasma dispersion.
Pritchett, P. L.↗
Plasma wave observations at Neptune
Phenomena detected by the plasma wave instrument during the Voyager 2 flyby of Neptune are reviewed. Particular attention given to radio emissions, electron plasma oscillations in the solar wind upstream of the bow shock, electrostatic electron cyclotron waves and upper hybrid resonance (UHR) waves, whistler mode noise, and dust impacts. The radio emissions which occur in a broad range of about 5 to 50 kHz are considered to be generated by mode conversion from UHR waves at the magnetic equator. The inner magnetosphere has relatively low plasma wave intensities (less than 100 microV/m). Many small micron-sized dust particles which were detected striking the spacecraft had the maximum impact rate of about 280 impacts per sec at the bound ring plane crossing, and about 110 impacts per sec at the outbound ring plane crossing. Most of the particles were concentrated in a dense disk, about one thousand km thick, near the equatorial plane.
Gurnett, D. A.↗
Electromagnetic and electrostatic emissions at the cusp-magnetosphere interface during substorms
Strongly peaked electrostatic emissions near 10.0 kHz and electromagnetic emissions near 0.56 kHz have been observed by the VLF wave detector on board Imp 6 on crossings from the earth's magnetosphere into the polar cusp during the occurrence of large magnetospheric substorms. The electrostatic emissions were observed to be closely confined to the cusp-magnetosphere interface. The electromagnetic emissions were of somewhat broader spatial extent and were seen on higher-latitude field lines within the cusp. Using these plasma wave observations and additional information provided by plasma, magnetometer and particle measurements made simultaneously on Imp 6, theories are constructed to explain each of the two classes of emission. The electromagnetic waves are modeled as whistlers, and the electrostatic waves as electron-cyclotron harmonics. The resulting growth rates predict power spectra similar to those observed for both emission classes. The electrostatic waves may play a significant role via enhanced diffusion in the relaxation of the sharp substorm time cusp-magnetosphere boundary to a more diffuse quiet time boundary.
Curtis, S. A.↗
Pulse-stimulated emission from plasma columns.
Pulse stimulated emission from plasma columns, discussing decaying ringing at electron- cyclotron frequency
Baldwin, D. E.↗
Planetary plasma waves
The primary types of plasma waves observed in the vicinity of the planets Venus, Mars, Earth, Jupiter, Saturn, Uranus, and Neptune are described. The observations are organized according to the various types of plasma waves observed, ordered according to decreasing distance from the planet, starting from the sunward side of the planet, and ending in the region near the closest approach. The plasma waves observed include: electron plasma oscillations and ion acoustic waves; trapped continuum radiation; electron cyclotron and upper hybrid waves; whistler-mode emissions; electrostatic ion cyclotron waves; and electromagnetic ion cyclotron waves.
Gurnett, Donald A.↗
An upper limit to coronal X-rays from single, magnetic white dwarfs
Pointed ROSAT Position Sensitive Proportional Counter (PSPC) exposures of 9277 and 6992 sec, directed toward the nearby, single, cool, magnetic white dwarfs GR 290 and EG 250 yielded no counts significantly above the expected background rate. The corresponding flux limits (for an assumed source temperature of 1 keV) are 1.0 and 1.7 x 10(exp -14) erg/sq cm/s, within the 0.1-2.5 keV bandpass of the instrument (99% confidence limits). This is more than an order of magnitude below the tentative detection level (for GR 290) and limits (for four other similar stars) obtained from archival Einstein data in 1991. The corresponding limits on coronal electron density are comparable with those implied if cyclotron emission is not responsible for any of the features observed in the optical spectra of magnetic white dwarfs. X-ray data currently provide no evidence for the existence of coronae around these stars. A final long observation (25,000 sec of GD 356) is scheduled for later this year on ROSAT, along with coordinated Extreme Ultraviolet Explorer (EUVE) observations.
Cavallo, Rob↗
Exoplanets and Radio Astronomy Beyond Earth
Jupiter's radio emission has been linked to its planetary-scale magnetic field, and spacecraft investigations have revealed that most planets, and some moons, have or had a global magnetic field. Generated by internal dynamos, magnetic fields are one of the few remote sensing means of constraining the properties of planetary interiors. For the Earth, its magnetic field has been speculated to be partially responsible for its habitability, and knowledge of an extrasolar planet's magnetic field may be necessary to assess its habitability. The radio emission from Jupiter and other solar system planets is produced by an electron cyclotron maser, and detections of extrasolar planetary electorn cyclotron masers will enable measurements of extrasolar planetary magnetic fields. Key advances would include the ground-based detection of the radio emission from Jovian-mass planets and laying the technological foundations for space-based detections of the radio emissions from lower-mass planets.
Lazio, Joseph↗
A test of incoherent Cerenkov radiation for VLF hiss and other magnetospheric emissions
Consideration of incoherent Cerenkov radiation from intense fluxes of electrons in the magnetosphere as a source of VLF hiss and several other emission phenomena. A procedure for calculating the Cerenkov and cyclotron radiation power from a spectrum of electrons in a test volume is outlined, as well as a ray-tracing routine for determining the path that the emitted power follows through the magnetosphere. Comparisons are made between a VLF hiss event and an energetic particle spectrum observed simultaneously with the Injun 5 spacecraft. Calculated power and fields for incoherent Cerenkov radiation are two orders of magnitude below the observed VLf hiss values, although the spectral shapes are similar. It is concluded that a partially coherent or amplified Cerenkov source or an instability is located in the altitude range from 3000 to 10,000 km. Calculations regarding Cerenkov radiation as a possible source for other wave phenomena indicate that upper hybrid resonance noise and fast hisslers may be understood in terms of incoherent Cerenkov radiation, but that V-shaped VLF hiss, saucers, ELF hiss, and Io-related Jovian decametric radiation may not.
Taylor, W. W. L.↗
Theory of decametric radio emissions from Jupiter.
It is suggested that the Jovian decametric emissions (DAM) originate in a cyclotron instability of weakly relativistic electrons trapped in the Jovian magnetic field. The resulting radiation has a group velocity in the magnetospheric plasma which may be of order 100 km/sec, and thus takes much more time to escape the magnetosphere than if the group velocity were at or near the speed of light. Therefore, the asymmetry of the Io phase with respect to sources east and west of the Earth-Jupiter line does not imply an asymmetric beaming of DAM; it is caused by the delay the waves experience in traversing the magnetosphere. The frequency drifts of milli- and decasecond bursts are also explained.
Wu, C. S.↗
Ordinary mode radio emission from Uranus
On Jan. 24, 1986, during the inbound trajectory to Uranus, the planetary radio astronomy instrument on Voyager 2 detected left-hand-polarized emission for several hours at frequencies near 200 kHz. Unlike the dominant source observed on the nightside of the planet, only a single episode of this inbound emission was seen, and the emission was extremely weak. Generating less than 500 kW, it is probably the weakest freely propagating planetary radio emission thus far observed by Voyager. This weak emission is associated with a source region in the vicinity of the north (dayside) magnetic pole of Uranus, where magnetic-field lines point approximately in the direction of the spacecraft when the emission is observed. Therefore the wave normal angle relative to B is probably less than 90 deg in the generation region. It is concluded that direct wave generation in the magnetoionic ordinary mode is most likely. The source location for this emission is consistent with a region magnetically conjugate to the dominant nightside source, which is located in the vicinity of the south magnetic pole. The ordinary mode emission is discussed in the context of the electron-cyclotron maser mechanism.
Desch, M. D.↗
Stimulated emission of AKR in regions of a weakly unstable electron velocity distribution
While, according to the cyclotron maser theory, auroral kilometric radiation generates auroral zone instability whose consequent radiation is in many respects consistent with observations, in situ velocity distribution measurements by satellites show only moderate positive gradients which would be only marginally unstable, implying a low radiation level. Numerical simulations are conducted alternatively using an observed electron-velocity distribution and an idealized loss-cone distribution. The expected amplification of X-mode radiation, as well as effects which go beyond the behavior of a simple amplifying medium, emerge in the results.
Kainer, S.↗
A broad-band VLF-burst associated with ring-current electrons
Frequency band broadening takes place just outside of the nighttime plasmasphere, where the density of cold plasma is known to be very low during the later phase of a geomagnetic storm. Instead of the gradual broadening of several hours duration, a burst type broadening of VLF emission lasting less than ten minutes was observed by Explorer 45 in a similar location. The magnetic field component of this emission is very weak and the frequency spreads below the local half electron cyclotron frequency. Corresponding enhancement of the anisotropic ring current electrons is also very sudden and limited below the order of 10 keV without significant velocity dispersion, in contrast to the gradual broadening events. The cause of this type of emission band spreading can be attributed to the generation of the quasielectrostatic whistler mode emission of short wavelength by hot bimaxwellian electrons surging into the domain of relatively low density magnetized cold plasma. The lack of energy dispersion in the enhanced electrons indicates that the inner edge of the plasma sheet, the source of these hot electrons, is not far from the location of this event.
Maeda, K.↗