Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “electron beam stability”

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.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Strongly turbulent stabilization of electron beam-plasma interactions

The stabilization of electron beam interactions due to strongly turbulent nonlinearities is studied analytically and numerically for a wide range of plasma parameters. A fluid mode coupling code is described in which the effects of electron and ion Landau damping and linear growth due to the energetic electron beam are included in a phenomenological manner. Stabilization of the instability is found to occur when the amplitudes of the unstable modes exceed the threshold of the oscillating two-stream instability. The coordinate space structure of the turbulent spectrum which results clearly shows that soliton-like structures are formed by this process. Phenomenological models of both the initial stabilization and the asymptotic states are developed. Scaling laws between the beam-plasma growth rate and the fluctuations in the fields and plasma density are found in both cases, and shown to be in good agreement with the results of the simulation.

Freund, H. P.↗
NASA NTRS1983

Measurements of the stability of energetic electron beams in the ionosphere

An electron gun carried in the main payload of a rocket launched on December 3, 1979 into a bright, east-west oriented auroral arc produced a pulsed electron beam in a programed format. Charged particle observations from the flight are used to define the spatial distribution of perturbed volume surrounding the accelerator during gun firing, determining that perturbation radial dimensions scale with the primary electron beam gyroradius and current and are dependent on beam injection angle. The intense flux of low energy electrons observed on field lines near the rocket are shown to be accelerated ambients, while particles at or near the beam energy and at large radial distances are presumably beam primaries. Results from this flight are compared with those from large vacuum tank simulations, and it is concluded that certain features of the data are consistent with the beam-plasma instability observed in the laboratory.

Duprat, G. R. J.↗
NASA NTRS1993

Microstructural stability of wrought, laser and electron beam glazed NARloy-Z alloy at elevated temperatures

Microstructure of wrought, laser, and electron-beam glazed NARloy-Z(Cu-3 wt.% Ag-0.5 wt.% Zr) was investigated for thermal stability at elevated temperatures (539 to 760 C (1,100 to 1,400 F)) up to 94 h. Optical and scanning electron microscopy and electron probe microanalysis were employed for studying microstructural evolution and kinetics of precipitation. Grain boundary precipitation and precipitate free zones (PFZ's) were observed in the wrought alloy after exposing to temperatures above 605 C (1,120 F). The fine-grained microstructure observed in the laser and electron-beam glazed NARloy-Z was much more stable at elevated temperatures. Microstructural changes correlated well with hardness measurements.

Singh, J.↗
NASA NTRS1983

Image motion compensation by area correlation and centroid tracking of solar surface features

An experimental solar correlation tracker was tested and evaluated on a ground-based solar magnetograph. Using sunspots as fixed targets, tracking error signals were derived by which the telescope image was stabilized against wind induced perturbations. Two methods of stabilization were investigated; mechanical stabilization of the image by controlled two-axes motion of an active optical element in the telescope beam, and electronic stabilization by biasing of the electron scan in the recording camera. Both approaches have demonstrated telescope stability of about 0.6 arc sec under random perturbations which can cause the unstabilized image to move up to 120 arc sec at frequencies up to 30 Hz.

Nein, M. E.↗
NASA NTRS1998

Evidence for Langmuir Envelope Solitons in Solar Type III Burst Source Regions

We present observational evidence for the generation of Langmuir envelope solitons in the source regions of solar type III radio bursts. The solitons appear to be formed by electron beams which excite either the modulational instability or oscillating two-stream instability (OTSI). Millisecond data from the Ulysses Unified Radio and Plasma Wave Experiment (URAP) show that Langmuir waves associated with type III bursts occur as broad intense peaks with time scales ranging from 15 to 90 milliseconds (6 - 27 km). These broad field structures have the properties expected of Langmuir envelope solitons, viz.: the normalized peak energy densities, W(sub L)/n(sub e)T(sub e) approximately 10(exp -5), are well above the modulational instability threshold; the spatial scales, L, which range from 1 - 5 Langmuir wavelengths, show a high degree of inverse correlation with (W(sub L)/n(sub e)T(sub e))(sup 1/2); and the observed widths of these broad peaks agree well with the predicted widths of envelope solitons. We show that the orientation of the Langmuir field structures is random with respect to the ambient magnetic field, indicating that they are probably isotropic structures that have evolved from initially pancake-like solitons. These observations suggest that strong turbulence processes, such as the modulational instability or the OTSI, stabilize the electron beams that produce type III bursts.

Thejappa, G.↗
NASA NTRS2012

Phase Coupling in Langmuir Wave Packets: Evidence for Four Wave Interactions in Solar Type III Radio Bursts

The four wave interaction process, known as the oscillating two stream instability (OTSI) is considered as one of the mechanisms responsible for stabilizing the electron beams associated with solar type III radio bursts. It has been reported that (1) an intense localized Langmuir wave packet associated with a type III burst contains the spectral characteristics of the OTSI: (a) a resonant peak at the local electron plasma frequency, f(sub pe), (b) a Stokes peak at a frequency slightly lower than f(sub pe), (c) anti-Stokes peak at a frequency slightly higher than f(sub pe), and (d) a low frequency enhancement below a few hundred Hz, (2) the frequencies and wave numbers of these spectral components satisfy the resonance conditions of the OTSI, and (3) the peak intensity of the wave packet is well above the thresholds for the OTSI as well as spatial collapse of envelope solitons. Here, for the first time, applying the trispectral analysis on this wave packet, we show that the tricoherence, which measures the degree of coherent four-wave coupling amongst the observed spectral components exhibits a peak. This provides an additional evidence for the OTSI and related spatial collapse of Langmuir envelope solitons in type III burst sources.

Thejappa, G.↗
NASA NTRS1980

The application of artificial electron beams to magnetospheric research

Scientific and technical progress made in the utilization of electron beams injected from large sounding rockets for the investigation of magnetospheric structure and dynamics and plasma physics is reviewed. Consideration is given to the problem of vehicle neutralization during the generation of electron beams in the ionosphere and the stability and electromagnetic wave emissions of electron beams propagating in space. Optical effects observed during the two Hess artificial aurora experiments, the Minnesota Echo IV and V experiments, the Zarnitsa-1 artificial aurora experiment and the Precede-Excede experiments are discussed, together with atmospheric scattering effects observed during Echo I, II and III, and results of the three experimental programs which have detected and analyzed beams after passage through the distant magnetosphere (the second Hess experiment, ARAKS and the Electron Echo experiments) are presented. Finally, plans for future research are outlined, and a chronology and complete bibliography of the programs conducted to date are included.

Winckler, J. R.↗
NASA NTRS1995

Energy measurement of electron beams by Compton scattering

A method has been proposed to utilize the well-known Compton scattering process as a tool to measure the centroid energy of a high energy electron beam at the 0.01% level. It is suggested to use the Compton scattering of an infrared laser off the electron beam, and then to measure the energy of the scattered gamma-rays very precisely using solid-state detectors. The technique proposed is applicable for electron beams with energies from 200 MeV to 16 GeV using presently available lasers. This technique was judged to be the most viable of all those proposed for beam energy measurements at the nearby Continuous Electron Beam Accelerator Facility (CEBAF). Plans for a prototype test of the technique are underway, where the main issues are the possible photon backgrounds associated with an electron accelerator and the electron and laser beam stabilities and diagnostics. The bulk of my ASEE summer research has been spent utilizing the expertise of the staff at the Aerospace Electronics Systems Division at LaRC to assist in the design of the test. Investigations were made regarding window and mirror transmission and radiation damage issues, remote movement of elements in ultra-high vacuum conditions, etc. The prototype test of the proposed laser backscattering method is planned for this December.

Keppel, Cynthia↗
NASA NTRS2002

The Propagation and Formation of Electron Holes

One of the striking findings of the International Solar Terrestrial Physics (ISTP) program is the detection of electron holes by several satellites in different regions of the magnetosphere, near the bow shock, and in the solar wind. These measurements have come from FAST (Fast Auroral Snapshot Explorer), Polar, Geotail, and Wind satellites. Using a 2-D (two dimensional) PIC (particle in cell) code we investigate the parameters of one and two electron beams on the evolution, structure, and stability of electron phase-space holes.

Coffey, Victoria↗
NASA NTRS1981

Electron beam induced damage in ITO coated Kapton

Data for the stability of thin conductive indium tin oxide films on 0.003 inch thick Kapton substrates during exposure of the surface to electron beams are reported. The electron beam energy was 3 keV and the diameter was about 0.8 mm. Thermal effects and surface modifications are considered. For primary current greater than 0.6 microamperes, an obvious dark discoloration with diameter approximately that of the beam was produced. The structure of the discolored region was studied with the scanning electron microscope, and the findings are stated. Surface modifications were explored by AES, obtaining spectra and secondary emission coefficient as a function of time for different beam intensities. In all cases beam exposure results in a decrease of the secondary yield but because of thermal effects this change, as well as composition changes, cannot be directly interpreted in terms of electron beam dosage.

Krainsky, I.↗
NASA NTRS1971

Electron dynamics and energy conversion in O-type linear-beam devices.

A general nonlinear interaction theory is used to investigate the effects of transverse fields (i.e., radial circuit fields and radial space-charge fields) in traveling-wave amplifiers for a variety of beam-focusing conditions. Magnetic focusing fields which are periodic or tapered (increased) with distance along the device are considered in addition to uniform magnetic fields. Results are presented for Brillouin flow and near-Brillouin flow, and the minimum magnetic field strength required to effectively constrain the electron beam is determined as a function of the operating parameters for the various focusing systems. Confined flow is also examined for the uniform-field case in order to have a basis of comparison from which the effects of radial motion of the beam electrons can be determined. The results indicate the importance of transverse effects and further yield information on the stability of strongly modulated cylindrical electron beams.-

Detweiler, H. K.↗