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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Cosmic-ray electrons and galactic radio emission - A conflict

An analysis which takes into account the observed energy spectrum of cosmic-ray electrons above 5 GeV and calculated mean magnetic field data shows that the observed spectral index of the radio continuum in the Galaxy is in conflict with some of the cosmic-ray electron measurements. It is found that the absolute intensities of cosmic-ray electrons measured by some of the experimenters are so low that they cannot be reconciled either with the interstellar magnetic field limits or with the extent of the galactic disk toward the anticenter.

Badhwar, G. D.↗
NASA NTRS1981

Energetic electrons, Type III radio bursts, and impulsive solar flare X-rays

Observations of impulsive hard X-ray and type III radio bursts made during the maximum of the last solar activity cycle are analyzed. Spectral measurements of 10-68 keV X-rays were made with the University of California (Berkeley) experiment aboard the OGO 5 satellite. About 20% of impulsive hard X-ray bursts are correlated with type III radio bursts, whereas only about 3% of the reported type III radio bursts are correlated with impulsive X-ray bursts. The location of the associated H gamma flare on the solar disk has little effect on the X-ray-type III burst correlation. The magnitude of the X-ray-type III burst correlation increases systematically with an increase in the intensity and starting frequency of the radio burst, the peak energy and hardness of the X-ray burst, and the peak nonthermal emission measure and spectral hardness of the electron spectrum not less than 20 keV inside the X-ray source. Observations are consistent with the electron populations responsible for both the X-ray and type III emissions accelerated in a single acceleration process; they also suggest a flare model where the primary instability causing electron acceleration during the impulsive phase occurs in the corona.

Kane, S. R.↗
NASA NTRS1987

The speeds of electrons that excite solar radio bursts of type III

Evidence is presented that solar type III radio bursts at kilometric wavelengths are excited by electrons with average speeds of 0.14 c; i.e., in good agreement with in situ measurements by Lin et al. (1981; 1986), but considerably lower than the generally accepted values of 0.3 to 0.5 c. A set of 28 bursts for which electrons and/or plasma waves were observed at ISEE-3 is examined, and it is found that the initial parts of all bursts were due to plasma radiation at the fundamental, and that the fastest electrons that produce radio emission range from 0.25 c down to 0.07 c (average 0.14 c). The slower electrons, those that produce fundamental radiation at approximately the time of burst peak, have an average speed of 0.06 c and a range from about 0.10 c down to 0.03 c.There is no evidence in the data for a systematic increase or decrease of exciting electron speed with distance from the sun.

Dulk, G. A.↗
NASA NTRS1980

Radio emission, cosmic ray electrons, and the production of gamma-rays in the Galaxy

The paper examines the traditional derivation of the interstellar electron spectrum using the galactic nonthermal radio spectrum and new radio data. The radio spectrum derived in the polar directions is now used as a base for this derivation instead of the anticenter spectrum. The exponent is determined for the interstellar electron spectrum between 70 and 1200 MeV, and radio maps are used to predict the gamma-ray fluxes produced by the bremsstrahlung process expected from these electrons. The differences in the predicted and observed gamma-ray intensities in the galactic plane are small, but in the polar direction the predicted gamma-ray flux using radio data is six times larger than that actually observed.

Webber, W. R.↗
NASA NTRS1978

Plasma density mapping in the solar wind through use of VHF radio to measure electron content

How the electron content between the Solar probe and the earth can be observed with a minimum of equipment and give a quantitative rationale for the use of a signal near 400 MHz to supplement the telecommunications signal is described. The emphasis is on the method of making content observations and on their value. While far from the Sun, the electron content is so low that the S-X dual-frequency system is insufficiently sensitive and a UHF system is optimum. As the probe approaches the Sun, the UHF may be disrupted by scintillation and the variations of the telecommunications signal must be used for the content measurement. By operating the suggested system in different modes as the solar distance changes, operation during the entire mission is possible.

Croft, T. A.↗
NASA NTRS2009

Non-ambipolar radio-frequency plasma electron source and systems and methods for generating electron beams

An electron generating device extracts electrons, through an electron sheath, from plasma produced using RF fields. The electron sheath is located near a grounded ring at one end of a negatively biased conducting surface, which is normally a cylinder. Extracted electrons pass through the grounded ring in the presence of a steady state axial magnetic field. Sufficiently large magnetic fields and/or RF power into the plasma allow for helicon plasma generation. The ion loss area is sufficiently large compared to the electron loss area to allow for total non-ambipolar extraction of all electrons leaving the plasma. Voids in the negatively-biased conducting surface allow the time-varying magnetic fields provided by the antenna to inductively couple to the plasma within the conducting surface. The conducting surface acts as a Faraday shield, which reduces any time-varying electric fields from entering the conductive surface, i.e. blocks capacitive coupling between the antenna and the plasma.

Hershkowitz, Noah↗
NASA NTRS2011

Non-ambipolar radio-frequency plasma electron source and systems and methods for generating electron beams

An electron generating device extracts electrons, through an electron sheath, from plasma produced using RF fields. The electron sheath is located near a grounded ring at one end of a negatively biased conducting surface, which is normally a cylinder. Extracted electrons pass through the grounded ring in the presence of a steady state axial magnetic field. Sufficiently large magnetic fields and/or RF power into the plasma allow for helicon plasma generation. The ion loss area is sufficiently large compared to the electron loss area to allow for total non-ambipolar extraction of all electrons leaving the plasma. Voids in the negatively-biased conducting surface allow the time-varying magnetic fields provided by the antenna to inductively couple to the plasma within the conducting surface. The conducting surface acts as a Faraday shield, which reduces any time-varying electric fields from entering the conductive surface, i.e. blocks capacitive coupling between the antenna and the plasma.

Hershkowitz, Noah↗
NASA NTRS2003

Near-Relativistic Solar Electrons and Type III Radio Bursts

Recently it has been found that the inferred injection times of greater than 25 keV electrons are up to 30 minutes later than the start times of the associated type III radio bursts at the Sun. Thus it has been suggested that the electrons that produce type III bursts do not belong to the same population as those observed above 25 keV. This paper examines the characteristics and circumstances of 79 solar electron beam events measured on the ACE spacecraft. Particular attention is paid to the very low frequency emissions of the associated radio bursts and the ambient conditions at the arrival times of the electrons at the spacecraft. It is found that the inferred greater than 25 keV electron injection delays are correlated with the times required for the associated radio bursts to drift to the lowest frequencies. This suggests that the electrons responsible for the radio emission and those observed above 25 keV are part of a single population, and that the electrons both above and below 25 keV are delayed in the interplanetary medium. Further evidence for a single population is the general correspondence between electron and local radio intensities and temporal profiles. It is found that the delays increase with the ambient solar wind density consistent with the propagation times of the electrons being determined by the characteristics of the interplanetary medium. However it is known that particle arrival times at 1 AU are a linear function of inverse particle speed. Conventionally such a relationship is taken to indicate scatter-free propagation when inferred path lengths lie close to 1.2 AU, as they do for the electron events studied here. These conflicting interpretations require further investigation.

Cane, H. V.↗
DOE OSTI2026

Suprathermal electron transport studies in radio-frequency-heated tokamak plasmas

This contribution reports on the study of suprathermal electron radial transport enhancement in the presence of electron-heating radio-frequency waves, such as electron-cyclotron waves or lower-hybrid waves. Since suprathermal electrons emit hard X-rays from Bremsstrahlung, experimental data from hard X-ray measurements are used to follow their dynamics. In particular, electron-cyclotron power modulation experiments performed in TCV show that this transport depends on the total electron-cyclotron power. These results are corroborated by experimentally constrained Fokker-Planck simulations [J. Cazabonne et al, Plasma Phys. Control. Fusion 65, 104001 (2023)]. Similar experiments have been performed in WEST with lower-hybrid waves, and are reported for the first time. Preliminary analyses show potential evidence of suprathermal electron transport, but no clear dependence on wave power nor photon energy at this stage.

Cazabonne, Jean [CEA, IRFM, Saint Paul Lez Durance↗
NASA NTRS1975

Quantitative comparisons of type 3 radio burst intensity and fast electron flux at 1 AU

The flux of fast solar electrons and the intensity of the type 111 radio emission generated by these particles were compared at one AU. Two regimes were found in the generation of type 111 radiation: one where the radio intensity is linearly proportional to the electron flux, and another, which occurs above a threshold electron flux, where the radio intensity is approximately proportional to the 2.4 power of the electron flux. This threshold appears to reflect a transition to a different emission mechanism.

Fitzenreiter, R. J.↗
NASA NTRS1976

Quantitative comparisons of type III radio burst intensity and fast electron flux at 1 AU

We compare the flux of fast solar electrons and the intensity of the type III radio emission generated by these particles at 1 AU. We find that there are two regimes in the generation of type III radiation: one where the radio intensity is linearly proportional to the electron flux, and the second regime, which occurs above a threshold electron flux, where the radio intensity is proportional to the approximately 2.4 power of the electron flux. This threshold appears to reflect a transition to a different emission mechanism.

Fitzenreiter, R. J.↗