Transport Of Energetic Electrons Research Articles

Model of energetic electron transport in magnetron discharges

A particle model of energetic electron transport in sputtering magnetron discharges is presented. The model assumes time-independent magnetic and electric fields and supposes that scattering by neutral atoms is the dominant transport mechanism. Without scattering, we find that some orbits are confined indefinitely. Using the differential cross sections for elastic, excitation, and ionization collisions in argon, we perform a Monte Carlo simulation of the electrons emitted by ion bombardment of a planar magnetron cathode to predict the spatial distribution of ionization. We find good agreement with experimental measurements of the radial profile of ion flux to the cathode and of the axial profile of optical emission.

Auroral excitation of the N2 2P(0,0) and VK(0,9) bands

The low‐energy secondary electron flux caused by auroral electron precipitation is examined using data from the Atmosphere Explorer C satellite. An energetic electron transport algorithm is used to compute the differential electron flux produced by measured primaries. Emissions of N2 in the 2P(0,0) band at 337 nm and the VK(0,9) band at 335 nm predicted by the model are compared with photometric observation of their combined volume emission rate altitude profile made by the visible airglow experiment. Reasonable correspondence between model and measurement is obtained. Ratios of emissions at 337 nm and 630 nm to the N2+ 1N(0,0) band at 428 nm are also studied. It is concluded that the 337/428 nm ratio responds to changes in the characteristic energy of primary auroral electrons only insofar as part of the 337 nm brightness is due to N2 VK(0,9) emission. The 630/428 nm ratio, which is strongly dependent on characteristic energy, also varies significantly with changes in atomic oxygen density.

Relativistic electrons near geostationary orbit: Evidence for internal magnetospheric acceleration

At times, relativistic electron fluxes in Earth's outer magnetosphere are not obviously related to an external (Jovian or solar) source. This finding suggests that an internal magnetospheric acceleration mechanism may operate under some circumstances. A possible mechanism identified for Jupiter's magnetosphere could also be considered in the terrestrial case. Such a model requires the substorm‐ generation of a spectrally‐soft electron component with subsequent inward radial diffusion (violating the third adiabatic invariant). A large electron energy gain transverse to the magnetic field occurs in this process. Eventually, deep within the magnetosphere, substantial pitch angle scattering occurs violating all adiabatic invariants. Then, at low L‐values, there occurs an energy‐preserving outward transport of energetic electrons near the mirror points. This leads to a return of the accelerated population to the outer magnetosphere. Such low‐altitude processes should result in “conic”quot; or “butterfly” pitch angle distributions at very high energies as the electrons execute trans‐L diffusion at the mirror altitudes and then are magnetically focussed near the equator. Data collected concurrently at geostationary orbit at three widely‐spaced local times during a relativistic electron event show a butterfly pitch angle distribution, while lower energy electrons simultaneously show pancake‐like distributions. The butterfly pitch angle distributions appear in ∼ 25% of the examined relativistic electron events, thereby providing support for acceleration by a recirculation process.

Coronal and interplanetary transport of solar energetic protons and electrons

We present a new method to separate interplanetary and coronal propagation, starting from intensity variations observed by spaceprobes at different heliolongitudes. In general, a decrease in absolute intensities is observed simultaneously with an increase in temporal delays. The coupling of these two effects can be described by Reid's model of coronal diffusion and can in principle be used to determine the two coronal time constants, diffusion time t c and escape time A. In addition, a least-squares fit method is used to determine the parameters of interplanetary transport, assuming a radial dependence as λ(r) = λ0(r/1 AU)b. The method is applied to the two solar events of 27 December, 1977 and 1 January, 1978 which were observed by the spaceprobes Helios 1, Helios 2, and Prognoz 6. Energetic particle data are analysed for 13–27 MeV protons and ∼-0.5 MeV electrons. For the regions in space encountered during these events the mean free path of electrons is smaller than that of protons. Straight interpolation between the two rigidities leads to a rather flat rigidity dependence λ(P) ∼ P n with n = 0.17–0.25. This contradicts the prediction of a constant mean free path or of the transition to scatter-free propagation below about 100 MV rigidity. In three of the four cases the mean free path of 13–27 MeV protons is of the order 0.17 AU, the mean free path of electrons of the order 0.06 AU. For protons we find b ∼- 0.7 for the exponent of the radial variation.

Importance of electron scattering with coupled plasmon-optical phonon modes in GaAs planar-doped barrier transistors

The GaAs planar-doped barrier (PDB) transistor is an MBE-grown structure which employs two unipolar homo junction barriers. One barrier, the emitter, injects energetic electrons into a thin n-type base region where these electrons are intended to experience negligible energy relaxation and thereby surmount the second (collector) barrier. Maximum common-base current gain or α values of 0.75 have been obtained at 77 K in experimental devices with base widths of 870 Å. Microwave measurements from 2 to 18 GHz on these devices imply a unity common-emitter current gain frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> of ∼ 40 GHz. The observed α values in other devices are unfortunately lower than those predicted by recent Monte Carlo simulations, and an unexpectedly strong dependence of α on ambient electron density in the base is noted. These are attributed to the previously overlooked electron scattering with coupled plasmon-optical phonon modes, and to electron-electron scattering. These scattering mechanisms must be included in any accurate model of energetic electron transport in GaAs in regions where the concentration of cooler ambient electrons is above 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> .

U.S. contributions to auroral aeronomy, 1979‐1982

Auroral aeronomy is the scientific discipline devoted to the study of the interaction of energetic particles and electric fields with the atmosphere of planets that have an appreciable intrinsic magnetic field. Specific topics that describe this interaction include: transport and energy degradation of energetic electrons and ions in a collision dominated medium, the excitation of atoms and molecules by collisions and by chemical reactions, the auroral spectrum, its production and interpretation, perturbations upon the ionospheric plasma in terms of enhanced ionization, composition, dynamics and heating, and perturbations upon the neutral atmosphere in terms of composition, dynamics and heating.It is not possible, however, to identify aeronomic processes as being uniquely relevant to the aurora because solar EUV photons and photoelectrons are subject to similar physical and chemical reactions leading to spectral emissions that also result from auroral electron bombardment of the atmosphere. Thus, a large segment of aeronomic research carried out during the quadrennium is reviewed in companion articles of this report to the I.U.G.G. An overview of Polar and Auroral Phenomena is presented by Reiff [1983, this issue]. She reviews auroral morphology, including pulsating aurora, emphasizing the relationship to magnetospheric phenomenology. Local and global characteristics of energetic particle precipitation are presented, and a summary of recent observations of energetic ions of ionospheric origin is given. Observations and theories on auroral electrodynamics are also reviewed by Reiff [1983], The effects of heating and ionization on Thermospheric Dynamics are reviewed by Roble [1983, this issue]. Progress in our understanding of the Neutral and Ion Composition of the Thermosphere is reported by Torr [1983, this issue]. This review focuses on reaction rate coefficients that are inferred from rockets and satellite observations of ion and neutral densities and optical emission rates, a technique that is particularly useful for studying metastable states of atmospheric gases. The chemical–ionic reactions pertinent to the dayglow are also relevant to the aurora so that progress in auroral aeronomy leans heavily on our understanding of the aeronomy at middle and low latitudes . Dynamical effects of auroral electric fields upon the high latitude ionosphere are discussed in the review by Richmond [1983, this issue]. The aurora and, in particular, the energetic solar proton events (SPE) significantly perturb the middle atmosphere, i.e. the mesosphere and upper stratosphere. Effects upon the chemistry and ionization are reviewed by Solomon [1983, this issue] while the dynamic and electrodynamic consequences are discussed, respectively, by Hartmann [1983, this issue] and by Kelly [1983, this issue].

Transport of energetic electrons in a fully ionized hydrogen plasma

A Monte Carlo method for calculating energetic electron transport in a plasma is presented. The energy loss and angular deflection due to Coulomb collisions as a function of travel distance and energy are derived for energetic electrons in a fully ionized plasma with a uniform magnetic field. Formulas which include the effect of nonuniform B fields on the angular deflection are derived. The Monte Carlo method is applied to the thick-target beam model in which the energetic electrons are injected vertically downward.

Energetic electrons in the magnetosheath and upstream of the bow shock

The characteristics and transport of &gt;200 keV electrons upstream of Earth's bow shock and in the outer magnetosheath are studied using nearly 4 years of data from the California Institute of Technology Electron/Isotope Spectrometer aboard IMP 8. In the upstream region, elevated electron intensities ranging from near the background level ∼0.1 (cm² s sr)−1 up to ∼100 (cm² s sr)−1 are observed about 2% of the time and typically persist for less than 5 min. These burst electrons stream intensely (ξ ∼ 0.5 to 1.5) sunward along the interplanetary magnetic field line. With the aid of a new coordinate system, it is demonstrated that the upstream bursts are most frequently seen on interplanetary field lines that trace to the inner magnetosheath, and that the total energy transported sunward by &gt;200 keV upstream electrons averages ∼1.6 × 1014 ergs/s, a figure comparable to the tailward energy flow observed in the permanent layer of energetic electrons adjacent to the magnetopause. Bursts of energetic electrons in the outer magnetosheath have time scales similar to those observed upstream, but they are typically ∼10 times more intense and much less anisotropic (ξ ≲ 0.4). The net flow of these electrons is toward the shock and very nearly equals the net flow away from the shock in the adjacent upstream region. The magnetosheath data suggest that energetic electron transport in this region may be described by a leaky box model with a scattering mean free path ∼0.6 RE. It is concluded that the energetic (&gt;200 keV) component of upstream electrons originates downstream of the bow shock. Energetic electrons in the upstream region, in the outer magnetosheath, and in the magnetopause electron layer appear to be closely related and probably have a common origin in the inner magnetosheath or possibly the magnetosphere.

A model for energetic electron transport in extragalactic radio sources

An investigation has been made of the Fokker-Planck equation for cosmic ray transport, with applications for extragalactic radio sources. The equation contains terms describing particle streaming, pitch angle scattering by magnetic irregularities, particle ''focusing'' by a nonuniform magnetic field, and energy loss due to synchrotron radiation. A method of solution of solution similar to that used by Earl has been employed, consisting of expansion of the electron distribution function in terms of the eigenfunctions of the scattering and focusing operators. An analytical solution for the expansion coefficients has been found. The coefficients are determined by the characteristic values of a matrix.

The role of energetic particle precipitation in Jovian magnetospherics: 1. Secondary electrons from the ionosphere of Jupiter

Escape of photoelectrons from the Jovian ionosphere produces only a meager source of thermal plasma for the inflated centrifugally unstable magnetosphere and is unable to account for the 100 eV thermal plasma temperatures of the magnetosphere. Since the Jovian magnetosphere is well populated with highly energetic electrons, the creation of secondaries and the energy degradation of the primaries precipitating into the lower ionosphere provide additional sources of magnetospheric thermal plasma as well as of the energy for further elevating the plasma temperatures in the top side ionosphere. The efficiencies with which escaping electrons are created by precipitating electrons with energies up to several MeV are computed using energetic electron transport and thermalization codes. The more energetic incident fluxes are far less efficient in creating escaping electrons than the lower energy fluxes with only 0.001% of the secondaries escaping for a 1 MeV source versus 3% for a 1 keV source. Incident fluxes of the order of 10 to 100 per sq cm per sec per eV between 100 eV and 100 keV are required to produce 50 eV escape fluxes comparable to those generated by solar EUV.

Model for the production and transport of energetic particles in a laser produced plasma

A model is presented for the production and transport of energetic electrons in a laser produced plasma. The basic assumption is that the laser deposits its energy in the form of a large amplitude plasma wave. The energy is given to particles as the electrostatic wave propagates outward and damps. Theory and simulations show that the maximum energetic particle velocity is between about five and seven thermal velocities, and that the heat flux is limited to about (1/4) nmV3e.