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Pitch angle distributions of electrons at dipolarization sites during geomagnetic activity: THEMIS observations
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Generation of Perpendicular Ion Acoustic Waves in the Ramp Region of Earth's Bow Shock in the Presence of a Flat‐Top Electron Velocity Distribution
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Ultrarelativistic electron butterfly distributions created by parallel acceleration due to magnetosonic waves
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Spatial distribution of energetic electrons in the geomagnetic tail.
Spatial distribution of energetic electrons in geomagnetic tail by analyzing counting rates from solid state detector on IMP I satellite
The angular distribution of ion flux around an ionospheric satellite.
Ion measurements from the Explorer 31 satellite were used to determine the angular distribution of ions around the satellite. The ion distributions were compared with the electron distributions measured on the same satellite. It is shown that the electron currents (fluxes) in the wake are always larger than the ion currents for a wide domain of plasma parameters. A quantitative comparison of the ion fluxes with a neutral approximation model for the angular distribution is considered. It is found that the ion fluxes become progressively larger than the corresponding computed neutral fluxes as the angle of attack increases from 0 to 180 deg.
Spatial Distribution of Energetic Electrons in the Geomagnetic Tail
Spatial distribution of energetic electrons in geomagnetic tail
Finite Gyroradius Effects in the Electron Outflow of Asymmetric Magnetic Reconnection
We present observations of asymmetric magnetic reconnection showing evidence of electron demagnetization in the electron outflow. The observations were made at the magnetopause by the four Magnetospheric Multiscale (MMS) spacecraft, separated by approximately 15 km. The reconnecting current sheet has negligible guide field, and all four spacecraft likely pass close to the electron diffusion region just south of the X line. In the electron outflow near the X line, all four spacecraft observe highly structured electron distributions in a region comparable to a few electron gyroradii. The distributions consist of a core with T(sub parallel) greater than T(sub perpendicular) and a nongyrotropic crescent perpendicular to the magnetic field. The crescents are associated with finite gyroradius effects of partly demagnetized electrons. These observations clearly demonstrate the manifestation of finite gyroradius effects in an electron-scale reconnection current sheet.
Microwave signature of thick-target electron beams in solar flares
The steady-state behavior of a flux of nonthermal electrons injected into a fully ionized thick target is examined. Owing to the (inverse square) energy dependence of the Coulomb collisional cross section, it is found that injected electron distributions that are monotonically decreasing functions of electron energy develop at finite depths into distributions that have 'humps' in velocity space; the electron energy corresponding to the hump correlates with the overlying particle column density to the target. This results in a two-stream unstable situation. The distribution is constantly being relaxed by quasi-linear relaxation and re-created by collisions; in this way a steady nonthermal level of Langmuir plasma waves is created, and these waves in turn produce microwave plasma radiation with a typical flux of 3 x 10 to the -16th erg/sq cm-sec. This flux can be enhanced by a factor of up to 100 by a high level of low-frequency (such as ion-acoustic) turbulence, which prevents quasi-linear relaxation for a sufficient fraction of the path length.
Coincident observations of ionospheric troughs and the equatorial plasmapause
Electron-density observations made in the topside ionosphere by the Ariel 4 and Isis 2 satellites are examined in conjunction with results obtained by Explorer 45 when it traversed the near-equatorial plasmapause with one hour (both UT and MLT) of the Ariel and Isis traversals of the same L coordinate. Both dusk and night observations are analyzed, and an attempt is made to show that depressions in ionospheric electron density occur in the vicinity of the plasmapause field line. It is concluded that the electron distributions observed in the electron-density troughs at 550 km near dusk by Ariel and at 1400 km near midnight by Isis do not always parallel variations in the light-ion distribution inferred from the Explorer plasmapause traversals and that there appears to be no specific feature of the main ionospheric trough which can be used to identify the plasmapause field line except in a statistical sense.
Electrostatic waves due to field-aligned electron beams in the low-latitude boundary layer
Mass-resolved ion, electron, and plasma wave data obtained from several low-latitude boundary layer (LLBL) crossings by the AMPTE CCE satellite are analyzed. The data clearly separate the LLBL from the adjacent magnetosheath and magnetosphere. Attention was focused on wave-particle interactions involving electrons. Electron beams were found to be present in the LLBL during the southward interplanetary magnetic field, along with a simultaneous enhancement of electrostatic waves with parallel polarization. Linear theory analysis shows that for plasma conditions in the LLBL, electron beams are unstable to electrostatic waves that propagate parallel to the local magnetic field, in agreement with observations. A numerical simulation study of the beam-plasma interaction in the LLBL shows that the instability saturates by thermalization of the beam but that a beamlike structure can still remain in the electron distribution for certain initial parameters. It is suggested that peaks in the electron velocity distribution function may be found in the LLBL away from the beam source region.
Electron pitch angle distributions throughout the magnetosphere as observed on Ogo 5.
A survey of the equatorial pitch angle distributions of energetic electrons is provided for all local times out to radial distances of 20 earth radii on the night side of the earth and to the magnetopause on the day side of the earth. In much of the inner magnetosphere and in the outer magnetosphere on the day side of the earth, the normal loss cone distribution prevails. The effects of drift shell splitting - i.e., the appearance of pitch angle distributions with minimums at 90 deg, called butterfly distributions - become apparent in the early afternoon magnetosphere at extended distances, and the distribution is observed in to 5.5 earth radii in the nighttime magnetosphere. Inside about 9 earth radii the pitch angle effects are quite energy-dependent. Beyond about 9 earth radii in the premidnight magnetosphere during quiet times the butterfly distribution is often observed. It is shown that these electrons cannot survive a drift to dawn without being considerably modified. The role of substorm activity in modifying these distributions is identified.
Simulations of electron beam excited modes in the high-altitude magnetosphere
Excitation of waves by electron distributions consisting of hot, beam, and cold populations is investigated theoretically and with the help of particle simulations. The main modes excited include the upper hybrid oscillation for nearly perpendicular propagation; the whistler mode at oblique angles, which becomes the plasma two-stream oscillation for parallel propagation; and the electron acoustic mode for nearly parallel propagation. The whistler mode, excited by thermal fluctuation enhancement, has a broad range of wave numbers and quasi-linearly decreases the beam slope, while the electron acoustic mode, which is linearly unstable, has a narrow spread in phase velocities and traps the beam and the warm electrons forming a double humped distribution. Both modes contribute to forming a tail in the cold electron distribution. The resulting wave spectrum is discussed in the context of DE 1 observations.
Single electron pulse height distribution of photomultipliers
Photomultipliers single electron response by measuring electron pulse height distribution
Direct electric field heating and acceleration of electrons in solar flares
We show that the observed properties of solar flare X-ray and microwave emission can be explained through the Joule heating and electric field acceleration of runaway electrons in current channels. The global properties of the flaring region required for this are presented. We have fit a hybrid thermal/nonthermal electron distribution, consisting of hot, isothermal electrons with a nonthermal tail of runaway electrons, to high-resolution hard X-ray and microwave spectra and have obtained excellent fits to both. The hybrid model relaxes the electron number and energy flux requirements for the hard X-ray emission over those of a purely nonthermal model. The model also provides explanations for several previously unexplained aspects of the high-resolution microwave spectra. The fit parameters can be related to physical properties (such as the electric field strength in the current channels) of the acceleration region.
Dual Electron Spectrometer for Magnetospheric Multiscale Mission: Results of the Comprehensive Tests of the Engineering Test Unit
The Magnetospheric Multiscale mission (MMS) is designed to study fundamental phenomena in space plasma physics such as a magnetic reconnection. The mission consists of four spacecraft, equipped with identical scientific payloads, allowing for the first measurements of fast dynamics in the critical electron diffusion region where magnetic reconnection occurs and charged particles are demagnetized. The MMS orbit is optimized to ensure the spacecraft spend extended periods of time in locations where reconnection is known to occur: at the dayside magnetopause and in the magnetotail. In order to resolve fine structures of the three dimensional electron distributions in the diffusion region (reconnection site), the Fast Plasma Investigation's (FPI) Dual Electron Spectrometer (DES) is designed to measure three dimensional electron velocity distributions with an extremely high time resolution of 30 ms. In order to achieve this unprecedented sampling rate, four dual spectrometers, each sampling 180 x 45 degree sections of the sky, are installed on each spacecraft. We present results of the comprehensive tests performed on the DES Engineering & Test Unit (ETU). This includes main parameters of the spectrometer such as energy resolution, angular acceptance, and geometric factor along with their variations over the 16 pixels spanning the 180-degree tophat Electro Static Analyzer (ESA) field of view and over the energy of the test beam. A newly developed method for precisely defining the operational space of the instrument is presented as well. This allows optimization of the trade-off between pixel to pixel crosstalk and uniformity of the main spectrometer parameters.
Random phase approximation for a plasma in an external electric field.
Random phase approximation for plasma, establishing perturbed electron distribution in oscillating electric field
Simultaneous wave and particle observations in the auroral kilometric radiation source region
Simultaneous observations from the topside sounder and the soft particle spectrometer onboard the ISIS 1 satellite reveal that very specific conditions on the local electron density and the energetic electron distributions must both occur in the auroral kilometric radiation (AKR) source region. Such regions are associated with inverted V electron precipitation and with depletions in the local electron density. The electron velocity distribution functions obtained near the inverted V peak were found to increase near several keV energy with increasing velocity as required for plasma instability. The electron density observed near the inverted V peak was too high to support AKR for three events investigated, however, and the AKR source was identified with the edge of the inverted V where the density was low (less than or equal to 30/cu cm) in each case. Whereas this density depletion can extend deep into the ionosphere (approximately 1500 km altitude), the severe depletion associated with the AKR density cavity is restricted to higher altitudes (greater than 2750 km for an event studied in detail).