Electron beam diagnostics.
Spectroscopic electron beam diagnostic technique, examining negligible effect elevated vibrational temperatures have on measured rotational temperatures of molecular nitrogen
ELECTRON BEAM↗
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Electron-Beam Diagnostic Methods for Hypersonic Flow Diagnostics
The purpose of this work was the evaluation of the use of electron-bean fluorescence for flow measurements during hypersonic flight. Both analytical and numerical models were developed in this investigation to evaluate quantitatively flow field imaging concepts based upon the electron beam fluorescence technique for use in flight research and wind tunnel applications. Specific models were developed for: (1) fluorescence excitation/emission for nitrogen, (2) rotational fluorescence spectrum for nitrogen, (3) single and multiple scattering of electrons in a variable density medium, (4) spatial and spectral distribution of fluorescence, (5) measurement of rotational temperature and density, (6) optical filter design for fluorescence imaging, and (7) temperature accuracy and signal acquisition time requirements. Application of these models to a typical hypersonic wind tunnel flow is presented. In particular, the capability of simulating the fluorescence resulting from electron impact ionization in a variable density nitrogen or air flow provides the capability to evaluate the design of imaging instruments for flow field mapping. The result of this analysis is a recommendation that quantitative measurements of hypersonic flow fields using electron-bean fluorescence is a tractable method with electron beam energies of 100 keV. With lower electron energies, electron scattering increases with significant beam divergence which makes quantitative imaging difficult. The potential application of the analytical and numerical models developed in this work is in the design of a flow field imaging instrument for use in hypersonic wind tunnels or onboard a flight research vehicle.
Source record↗
Impulsive H-alpha diagnostics of electron-beam-heated solar flare model chromospheres
Time-dependent H-alpha profiles were computed for the dynamic model atmospheres of Fisher, Canfield, and McClymont (1985) simulating the effects of an intense impulsively initiated power-law beam of electrons incident on the chromosphere. The temporal response of H-alpha arises from three separate physical mechanisms, whose relative importance varies over the line profile. The fastest variations (typically less than 0.1 s for the explosive heating discussed here) arise from energy imbalance; these are apparent on chromospheric heating and cooling time scales and have their greatest amplitude at line center. Slower variations arise from ionization imbalance and are most apparent in the blue wing. The slowest variations arise from hydrodynamic effects and are related to the formation of a chromospheric condensation; these are most apparent in the red wing. These results provide a basis for the design and analysis of observations of H-alpha, in coordination with hard X-rays or microwaves, to test mechanisms of energy transport in solar flares.
Canfield, Richard C.↗
Rarefied flow diagnostics using pulsed high-current electron beams
The use of high-current short-pulse electron beams in low-density gas flow diagnostics is introduced. Efficient beam propagation is demonstrated for pressure up to 300 microns. The beams, generated by low-pressure pseudospark discharges in helium, provide extremely high fluorescence levels, allowing time-resolved visualization in high-background environments. The fluorescence signal frequency is species-dependent, allowing instantaneous visualization of mixing flowfields.
Wojcik, Radoslaw M.↗
Suprathermal plasma observed on STS-3 Mission by plasma diagnostics package
Artificially produced electron beams were used extensively during the past decade as a means of probing the magnetosphere, and more recently as a means of actively controlling spacecraft potential. Experimentation in these areas has proven valuable, yet at times confusing, due to the interaction of the electron beam with the ambient plasma. The OSS-1/STS-3 Mission in March 1982 provided a unique opportunity to study beam-plasma interactions at an altitude of 240 km. On board for this mission was a Fast Pulse Electron Generator (FPEG). Measurements made by the Plasma Diagnostics Package (PDP) while extended on the Orbiter RMS show modifications of the ion and electron energy distributions during electron beam injection. Observations made by charged particle detectors are discussed and related to measurements of Orbiter potential. Several of the PDP instruments, the joint PDP/FPEG experiment, and observations made during electron beam injection are described.
Paterson, W.↗
Plasma heating, electric fields and plasma flow by electron beam ionospheric injection
The electric fields and the floating potentials of a Plasma Diagnostics Payload (PDP) located near a powerful electron beam injected from a large sounding rocket into the auroral zone ionosphere have been studied. As the PDP drifted away from the beam laterally, it surveyed a region of hot plasma extending nearly to 60 m radius. Large polarization electric fields transverse to B were imbedded in this hot plasma, which displayed large ELF wave variations and also an average pattern which has led to a model of the plasma flow about the negative line potential of the beam resembling a hydrodynamic vortex in a uniform flow field. Most of the present results are derived from the ECHO 6 sounding rocket mission.
Winckler, J. R.↗
Some Observations on Exhaust Recirculation from Clustered Rocket Nozzles
A short-duration rocket testing technique which exactly duplicates the combustion flows of multi-engine rocket boosters at high altitudes is described. The application of this technique to the investigation of the reverse flow characteristics of a 4-engine rocket cluster model is discussed. The use of a comparatively new diagnostic tool, the electron beam density probe, in mapping the recirculating flow field of a rocket cluster is described and experimental density results presented. Finally, the use of a reflection plane for the examination of reverse flow phenomena, whereby a plane of symmetry is replaced by a solid surface on which measurements may be made,is evaluated and experimental data presented.
Hendershot, K. C.↗
Whistler-mode radiation from the Spacelab 2 electron beam
During the Spacelab 2 mission the Plasma Diagnostics Package (PDP) performed a fly-around of the Shuttle at distances of up to 300 meters while an electron beam was being ejected from the Shuttle. A magnetic conjunction of the Shuttle and the PDP while the electron gun was operating in a steady (DC) mode is discussed. During this conjunction, the PDP detected a clear funnel-shaped emission that is believed to be caused by whistler-mode emission from the beam. Ray-path calculations show that the shape of the funnel can be accounted for by whistler-mode waves propagating near the resonance cone. Because the beam and waves are propagating in the same direction, the radiation must be produced by a Landau interaction with the beam. Other types of waves generated by the beam are also described.
Gurnett, D. A.↗
Artificial electron beams in the magnetosphere and ionosphere
The Plasma Diagnostics Payload of the Echo 7 satellite carried TV cameras and photometers by means of which the luminosity around an electron beam in the polar ionosphere could be studied. It was found that, while the beam Larmor spiral could be clearly seen near 100 km, above this only a column due to suprathermal electrons was observable. At high altitudes, the emission of neutral gas both generated powerful luminosity and substantially reduced accelerator potentials. An analysis of conjugate echoes indicates that inferred magnetospheric electric fields do not map well into the ionosphere, as well as the presence of strong pitch-angle scattering.
Winckler, John R.↗
An analysis of whistler mode radiation from the Spacelab 2 electron beam
During the Spacelab 2 mission the plasma diagnostics package (PDP) was released from the Shuttle to free fly. At times during this free flight, when the PDP was magnetically connected to the Shuttle, Stanford's fast-pulsed electron generator, located in the Shuttle cargo bay, ejected a 1-keV 50-mA electron beam. The PDP plasma-wave instrument detected intense whistler-mode radiation during these beam ejections. This paper presents a study of a whistler mode emission detected during one particular continuous electron beam firing. Calculations indicate that the beam radiated approximately 1.6 mW in the whistler mode as the beam traversed the 200 m from the Shuttle to the PDP. The emissivity also decreased by about a factor of 10 over this same distance. The measured wave powers are 10 to the 7th greater than wave powers expected from incoherent Cerenkov radiation, verifying that the radiation is generated by a coherent process. Estimates of the emissivity based on measured electric field intensities in the beam indicate that the whistler-mode noise is produced by radiation from electron bunches created by an electrostatic beam-plasma instability.
Farrell, W. M.↗
High resolution X-ray optics for astronomical and laboratory sources
In recent years X-ray telescopes have been used successfully for high resolution observations of astronomical objects, in particular the solar corona. At the present time X-ray microscopes are being developed for diagnostics of laser and electron beam induced fusion plasmas. This paper describes both types of imaging systems using as examples the AS&E X-ray telescope on Skylab and a 10X microscope being built for Los Alamos Scientific Laboratories. The designs, manufacturing tolerances, fabrication, testing, and performance are discussed. Steps for further development in both imaging areas are identified.
Silk, J. K.↗
Non-Intrusive Optical Diagnostic Methods for Flowfield Characterization
Non-intrusive optical diagnostic techniques such as Electron Beam Fluorescence (EBF), Laser-Induced Fluorescence (LIF), and Focusing Schlieren (FS) have been setup for high-speed flow characterization and large flowfield visualization, respectively. Fluorescence emission from the First Negative band of N2(+) with the (0,0) vibration transition (at lambda =391.44 nm) was obtained using the EBF technique and a quenching rate of N2(+)* molecules by argon gas was reported. A very high sensitivity FS system was built and applied in the High-Speed Flow Generator (HFG) at NASA LaRC. A LIF system is available at the Advanced Propulsion Laboratory (APL) on campus and a plume exhaust velocity measurement, measuring the Doppler shift from lambda = 728.7 nm of argon gas, is under way.
Tabibi, Bagher M.↗
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↗
Numerical simulations of impulsively heated solar flares
The response of a model solar atmosphere to heating by an electron beam has been studied for electron beam flux spectra which are power laws with low-energy 'knees' (rising linearly with time to a peak at 30 s and then falling linearly to 0 at 60 s) ranging from 10 to 20 keV. The results indicate that high peak electron beam fluxes, low-energy knees, and larger spectral indices all move the atmospheric response toward greater enhancements of the parameters in the coronal regions of the atmosphere. Coronal responses can thus be used as a diagnostic of the parameters of the electron beam.
Mariska, John T.↗
Double-probe potential measurements near the Spacelab 2 electron beam
As part of the Spacelab 2 mission the plasma diagnostics package (PDP) was released from the shuttle as a free-flying satellite. The PDP carried a quasi-static electric field instrument which made differential voltage measurements between two floating probes. At various times during the free flight, an electron beam was ejected from the shuttle. Large differential voltages between the double probes were recorded in association with the electron beam. However, analysis indicates that these large signals are probably not caused by ambient electric fields. Instead, they can be explained by considering three effects: shadowing of the probes from streaming electrons by the PDP chassis, crossing of the PDP wake by the probes, and spatial gradients in the fluxes of energetic electrons reaching the probes. Plasma measurements on the PDP show that energetic electrons exist in a region 20 m wide and up to at least 170 m downstream from the electron beam. At 80 or more meters downstream from the beam, the double probe measurements show that the energetic electron flux is opposite to the injection direction, as would be expected for a secondary returning electron beam produced by scattering of the primary electron beam.
Steinberg, J. T.↗
Electromagnetic-wave excitation in a large laboratory beam-plasma system
The mechanism by which unstable electrostatic waves of a beam-plasma system are converted into observed electromagnetic waves is of current interest in space physics and in tokamak fusion research. The process involved in the conversion of electrostatic to electromagnetic waves at the critical layer is well understood. However, the radiation from uniform plasmas cannot be explained on the basis of this process. In connection with certain difficulties, it has not yet been possible to establish the involved emission processes by means of experimental observations. In the considered investigation these difficulties are overcome by employing a large laboratory plasma in a parameter range suitable for detailed diagnostics. A finite-diameter electron beam is injected into a uniform quiescent afterglow plasma of dimensions large compared with electromagnetic wavelengths. The considered generation mechanism concerning the electromagnetic waves is conclusively confirmed by observing the temporal evolution of an instability
Whelan, D. A.↗
Coherent Cerenkov radiation from the Spacelab 2 electron beam
The plasma environment of the Spacelab 2 mission was investigated through the deployment of the Plasma Diagnostics Package (PDP) by the Space Shuttle Orbiter and the Orbiter's ejection of a continuous 1-keV/50-mA electron beam along a field line. As the PDP flew by the beam, its plasma-wave instrument detected intense whistler-mode radiation originating from the beam. A detailed model has been developed of the coherent Cerenkov emission process, using a one-dimensional computer simulation of the beam to model the expected phase space structure of the electrons. The power calculated for the modeled 200-m beam segment can easily account for the measured whistler mode wave power.
Farrell, W. M.↗
Three-dimensional simulation of whistler mode excited by the Spacelab 2 electron beam
During the Spacelab 2 mission, while an electron beam was being ejected from the Shuttle, the Plasma Diagnostics Package (PDP) detected a clear funnel-shaped emission that is believed to be caused by whistler-mode emission from the electron beam. In order to understand the mechanism of this emission, simulations with a three-dimensional partially magnetostatic code have been performed. The simulation results show that whistler-mode and lower hybrid waves are excited by the electron beam, which is initially localized in the column in the three-dimensional simulation system, and that they propagate away from the beam. The wave spectra of the electric and magnetic fields diagnosed at some points show several peaks due to the waves excited by the electron beam. The frequency range of these spectra is in qualitative agreement with the PDP data. The intense narrowband electrostatic emission near the electron plasma frequency is observed by the simulations. The simulation results show that the beam instability is responsible for the generation mechanism of these emissions.
Nishikawa, K.-I.↗