Trajectory observations for some spiraling electron beam systems
Trajectory observations for some spiraling electron beam systems using moveable probes and targets as well as photographic techniques
Wilmarth, R. W.↗
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Convection electric field effects on outer radiation belt electron precipitation
A model is presented for the possible diurnal modulation of outer radiation belt electron precipitation by considering the effect of the convection electric field on geomagnetically trapped electrons. The modulation flux is the flux due to electrons in the drift loss cone, i.e., those which drift into the bounce loss cone. The electron flux in the drift loss cone is related to the time allowable for diffusion from the stably trapped population to the drift loss cone for precipitation at a specific geographic location. This time, which is termed the maximum L-shell lifetime, is obtained by computing electron trajectories, using a realistic magnetic field model and a simple model for the electric field. The maximum L-shell lifetimes are taken to be the times between successive entries into the bounce loss cone. Conservation of the first two adiabatic invariants, as electrons are slowly energized by the convection electric field, leads to variations in pitch angle, maximum L-shell lifetimes, and, consequently, to changes in the electron flux in the drift loss cone. These results are compared with observations of precipitating electrons made with sounding rocket payloads.
Gelpi, C.↗
Theory of 2 omega(sub pe) radiation induced by the bow shock
A new radiation emission mechanism is proposed to explain electomagnetic radiation observed at twice the electron plasma frequency, 2 omega(sub pe), in the upstream region of the Earth's bow shock. This radiation had its origin at the electron foreshock boundary where energetic electron beams and intense narrow-band Langmiur waves are observed. The proposed emission mechanism results from the interaction of the electron beam and Langmuir waves that are backscattered off thermal ions. This interaction is described by a nonlinear dispersion equation which incorporates an effect owing to electron trajectory modulation by the backscattered Langmuir waves. Subsequent analysis of the dispersion equation reveals two important consequences. First, a long-wavelength electrostatic quasi-mode with frequency at 2 omega(sub pe) is excited, and second, the quasi-mode and the electomagnetic mode are nonlinearly coupled. The implication is that, when the excited 2 omega(sub pe) quasi-mode propagates in an inhomgeneous medium with slightly decreasing density, the quasi-mode can be converted directly into an electromagnetic mode. Hense the electomagnetic radiation at twice the plasma frequency is generated. Numerical solutions of the dispersion equation with the choice of parameters that describe physical characteristics of the electron foreshock are presented, which illustrates the viability of the new mechanism.
Yoon, Peter H.↗
Evaluation of magnetic refocusing in linear-beam microwave tubes
Magnetic field configurations in which the axial component of the field decays linearly to a constant plateau field are evaluated for use in refocusing the output beam of linear beam microwave tubes. The slope of the decay and the value of the plateau field are parameters in this study. A uniform beam with a space charge force only in the radial direction is assumed, and the electron trajectories are computed for various classes. For a given magnetic configuration (slope and plateau value) the plateau length is calculated for a specified class and the rms deviation of the output angles for all classes is computed at the end of this plateau length. A minimum condition for a refocused beam is defined to be one in which the rms value of the output angles is less than the rms input. Many of the configurations satisfied this criteria and successfully reduced the rms value by half.
Stankiewicz, N.↗
Three-dimensional evaluation of energy extraction in output cavities of klystron amplifiers
Description of an accurate three-dimensional mathematical model and computer program for calculating electronic interaction, electron trajectories, beam interception, and efficiency in the output cavity of a klystron amplifier. The highest computed efficiency for an optimally bunched beam was 80.3% with 6% ideal interception. Efficiency is shown to increase initially with interception.
Kosmahl, H. G.↗
Design and performance evaluation of small, two- and four-stage depressed collectors for a 4.8 to 9.6 GHz high-performance traveling wave tube
A program to improve the efficiency of traveling wave tubes (TWT's) for use in electronic countermeasure (ECM) systems by applying multistage depressed collector (MDC) and spent beam refocusing techniques is studied. Three dimensional electron trajectories are computed through-out the slow wave structure of the TWT, the spent beam refocuser, and the depressed collector. Both TWT and MDC performances are analytically evaluated.
Ramins, P.↗
Small-size 81- to 83.5-percent efficient 2- and 4-stage depressed collectors for octave-bandwidth high-performance TWT's
In a joint USAF-NASA Program, Lewis Research Center is carrying out an efficiency improvement program on traveling wave tubes for use in electronic counter measures by applying multistage depressed collector (MDC) and spent beam refocusing techniques. In the analytic part of the effort, three-dimensional electron trajectories are computed throughout the TWT. On the experimental side, tube performance is evaluated first without the MDC; then, the spent beam is analyzed for symmetry, circularity, and velocity spread. The three-dimensional theory predicts a MDC-efficiency, at mid-band, of 81 per cent for a 2-stage MDC with symmetric, circular, and optimally refocused beams and 85.5 per cent for a 4-stage MDC. Experimental results to date have yielded MDC efficiencies of a minimum of 81 and 83 per cent for a 2- and 4-stage MDC, respectively, across a one-octave bandwidth of a 4.8 to 9.6 GHz 330-to-550-W TWT.
Kosmahl, H. G.↗
Up-date of traveling wave tube improvements
NASA research in the area of traveling wave tube technology is reviewed, with emphasis on the basic physics of guns and collectors and a computer model for the interaction between the electron beam and the RF circuit. The design of a multistage depressed collector, capable of multiplying tube efficiency by a factor of two or more, is presented; one such design has been adopted for commercial traveling wave tube production. A three-dimensional model of electron trajectories toward the collector also receives attention, as does the problem of RF circuit losses.
Buck, E.↗
Design of high-perveance confined-flow guns for periodic-permanent-magnet-focused tubes
An approach to the design of high perveance, low compression guns is described in which confinement is used to stabilize the beam for subsequent periodic-permanent-magnet focusing. The computed results for two cases are presented. A magnetic boundary value problem was solved for the scalar potential from which the axial magnetic field was computed. A solution was found by iterating between Poisson's equation and the electron trajectory calculations. Magnetic field values were varied in magnitude until a laminar beam with minimum scalloping was produced.
Stankiewicz, N.↗
Dipole and quadrupole synthesis of electric potential fields
A general technique for expanding an unknown potential field in terms of a linear summation of weighted dipole or quadrupole fields is described. Computational methods were developed for the iterative addition of dipole fields. Various solution potentials were compared inside the boundary with a more precise calculation of the potential to derive optimal schemes for locating the singularities of the dipole fields. Then, the problem of determining solutions to Laplace's equation on an unbounded domain as constrained by pertinent electron trajectory data was considered.
Tilley, D. G.↗
The resolved layer of a collisionless, high beta, supercritical, quasi-perpendicular shock wave. III - Vlasov electrodynamics
The analysis of the fluid continuum level within the shock layer observed on November 7, 1977 by the ISEE satellites (Scudder et al., 1986) is extended to examine, within the framework of Vlasov electrodynamics, direct observational evidence for 'collisionless' resistivity. The analysis is based on the measured wave turbulence and the deviation of the observed electron velocity distribution function from the form predicted using the reversible individual electron trajectories in the presence of dc forces.
Scudder, J. D.↗
Comparison of Echo 7 field line length measurements to magnetospheric model predictions
The Echo 7 sounding rocket experiment injected electron beams on central tail field lines near L = 6.5. Numerous injections returned to the payload as 'conjugate echoes' after mirroring in the southern hemisphere. Field line lengths calculated from measured conjugate echo bounce times and energies are compared to predictions made by integrating electron trajectories through various magnetospheric models. Although Kp at launch was 3-, quiet time magnetic models best fit the echo measurements. Geosynchronous satellite magnetometer measurements near the Echo 7 field lines during the flight were best modeled by the Olson-Pfitzer Dynamic Model and the Tsyganenko-Usmanov model for Kp = 3. The discrepancy between the models that best fit the Echo 7 data and those that fit the satellite data was most likely due to uncertainties in the small-scale configuration of the magnetospheric models. The field line length measured by the conjugate echoes showed some temporal variation in the magnetic field, also indicated by the satellite magnetometers. This demonstrates the utility an Echo-style experiment could have in substorm studies.
Nemzek, R. J.↗
Reduction of PMT Signal-Induced Noise in Lidar Receivers
Signal-induced noise is generated when a photomultiplier tube (PMT) is subjected to an intense light pulse. The PMT signal does not return to the dark current level after the signal is removed, but decays slowly (i.e., signal-induced noise). This is of practical significance for DIAL (Differential Absorption lidar) measurements where signal-induced noise decays are superimposed on the on-line (absorption) and off-line signals. Errors in the ozone density calculation result for stratosphere measurements. Other researchers have implemented mechanical choppers that block the intense pulse which may be from near field return scattering or scattering from a cloud. This configuration cannot be implemented for the DIAL system employed for aircraft measurements since the on-line and off-line pulses are 300 microseconds apart. A scheme has been developed in this study to electronically attenuate the signal induced noise. A ring electrode, external to the PMT photocathode, is utilized to perturb the electron trajectories between the photocathode and the first dynode. This effect has been used for position sensitive PMTs and suggested for gating PMTS.
Williamson, Cynthia K.↗
A New Method for Reduction of Photomultiplier Signal-Induced Noise
For lidar measurements of ozone, photomultiplier tube (PMT) detector signal-induced noise represents a fundamental problem that complicates the extraction of information from lidar data. A new method is developed to significantly reduce signal-induced noise in lidar receiver PMT detectors. The electron optics of the lidar photomultiplier detector is modified to filter the source of signal-induced noise. A mesh electrode external to the PMT is utilized to control photoemission and disorient electron trajectories from the photocathode to the first dynode. Experiments were taken both with simulated and actual lidar return signals at Langley Research Center. Results show at least 40 percent more accurate ozone number density values with a mesh voltage of 60 V applied than with no voltage applied.
Koble, Andrea↗
Negative-ion formation in the explosives RDX, PETN, and TNT by using the reversal electron attachment detection technique
First results of a beam-beam, single-collision study of negative-ion mass spectra produced by attachment of zero-energy electrons to the molecules of the explosives RDX, PETN, and TNT are presented. The technique used is reversal electron attachment detection (READ) wherein the zero-energy electrons are produced by focusing an intense electron beam into a shaped electrostatic field which reverses the trajectory of electrons. The target beam is introduced at the reversal point, and attachment occurs because the electrons have essentially zero longitudinal and radial velocity. The READ technique is used to obtain the 'signature' of molecular ion formation and/or fragmentation for each explosive. Present data are compared with results from atmospheric-pressure ionization and negative-ion chemical ionization methods.
Boumsellek, S.↗
Reversal ion source - A new source of negative ion beams
A new type of ion source utilizing beams of electrons and target molecules, rather than a diffuse, volume plasma, is described. The source utilizes an electrostatic electron 'mirror' which reverses trajectories in an electron beam, producing electrons at their turning point having a distribution of velocities centered at zero velocity. A gas which attaches zero-velocity electrons is introduced at this turning point. Negative ions are produced by an attachment or dissociative attachment process. For many of the thermal electron-attaching molecules the cross sections can be quite large, varying as the inverse square root of the electron energy or just the s-wave threshold law. The efficiency and current density of the ion source for production of Cl(-) through the large, thermal energy attachment process is estimated. It is argued that the source can be used for the production of negative ions through attachment resonances located at higher energies as well.
Orient, O. J.↗
Large sounding rockets as a base for probing the distant magnetosphere
The Echo program's use of large sounding rockets to inject electron beams into the outer trapping region where the earth's plasma sheet interacts with the inner magnetosphere is discussed. The beams pass through the plasma sheet and the trapping region, reflect at the southern hemisphere conjugate point and return to the vicinity of the rocket where they are detected and analyzed for acceleration and diffusion processes which may also be responsible for the radiation belts. The motion of electron beams in the magnetosphere is discussed from the standpoint of single particle motion, and the trajectories of electrons injected with known energy, known angle between the electron velocity vector and the local magnetic field vector, and known position are examined. The interaction between the rocket motion and the electron drift motion is described, and the advantages and drawbacks of beam detection by optical methods and by throwaway detectors are compared. Planned Echo experiments using the Space Shuttle are discussed
Winckler, J. R.↗
Diurnal modulation of the quiet time penetrating electron flux
Three sounding rocket measurements of energetic electron precipitation in the 65 to 80 km altitude range above Siple Station, Antarctica suggest a possible diurnal modulation of the precipitation. Flights made on January 10 and 11, 1981, to investigate this possibility showed that no electrons were present after local noon, while a significant flux of penetrating electrons was observed the following day near local dawn, even though the level of magnetic activity was higher during the postnoon flight. A prevous flight from Siple Station also observed a large flux of penetrating electrons near local dawn. Calculations of electron drift trajectories in a model magnetic field indicate that moderate values of the convection electric field could cause significant local time variations in the penetrating electron flux at the western edge of the South Atlantic anomaly. These calculations indicate that Siple Station is shadowed by eastern Siberia when it is at local noon, but not when it is at local dawn.
Sheldon, W. R.↗