Engineering topics

Neubert, Torsten

Publications and source records attributed to Neubert, Torsten.

9 records

NASA NTRS2019

Climatology of Transient Luminous Events and Lightning Observed Above Europe and the Mediterranean Sea

In 1999, the first sprites were observed above European thunderstorms using sensitive cameras. Since then, Eurosprite campaigns have been conducted to observe sprites and other transient luminous events (TLEs), expanding into a network covering large parts of Europe and coastal areas. In 2009 through 2013, the number of optical observations of TLEs reached a peak of 2000 per year. Because of this unprecedented number of European observations, it was possible to construct a climatology of 8394 TLEs observed above 1018 thunderstorm systems and study for the first time their distribution and seasonal cycle above Europe and parts of the Mediterranean Sea. The number of TLEs per thunderstorm was found to follow a power law, with less than 10 TLEs for 801 thunderstorms and up to 195 TLEs above the most prolific one. The majority of TLEs were classified as sprites, 641 elves, 280 halos, 70 upward lightning, 2 blue jets and 1 gigantic jet. The climatology shows intense TLE activity during summer over continental areas and in late autumn over coastal areas and sea. The two seasons peak, respectively, in August and November, separated by March and April with almost no TLEs, and a relative minimum around September. The observed TLE activity, i.e. mostly sprites, is shown to be largely consistent with lightning activity, with a 1/1000 of observed TLE-to-lightning ratio in regions with most observations. The overall behaviour is consistent among individual years, making the observed seasonal cycle a robust general feature of TLE activity above Europe.

Arnone, Enrico↗

NASA NTRS1994

New aspects of whistler waves driven by an electron beam studied by a 3-D electromagnetic code

We have restudied electron beam driven whistler waves with a 3-D electromagnetic particle code. The simulation results show electromagnetic whistler wave emissions and electrostatic beam modes like those observed in the Spacelab 2 electron beam experiment. It has been suggested in the past that the spatial bunching of beam electrons associated with the beam mode may directly generate whistler waves. However, the simulation results indicate several inconsistencies with this picture: (1) whistler waves continue to be generated even after the beam mode space charge modulation looses its coherence, (2) the parallel (to the background magnetic field) wavelength of the whistler wave is longer than that of the beam instability, and (3) the parallel phase velocity of the whistler wave is smaller than that of the beam mode. The complex structure of the whistler waves in the vicinity of the beam suggest that the transverse motion (gyration) of the beam and background electrons is also involved in the generation of whistler waves.

Nishikawa, Ken-Ichi↗

NASA NTRS1993

A kinetic description of electron beam ejection from spacecraft

A model based on the Boltzmann kinetic equation describing electron beam ejection from spacecraft is presented. Results are shown for steady-state, beam-atmosphere interaction (BAI) and for beam-plasma interaction (BPI). The BPI considered is that of elastic scattering of beam electrons with strong, short-scale Langmuir turbulence. This mechanism has been suggested for prompt echoes of beam electrons observed in sounding rocket experiments. It is shown that the interaction is sufficiently strong to account for observations of back-scattered electrons at the beam accelerator energy. However, it is clear from observations that particles undergo diffusion in energy at a rate exceeding levels expected for BAI. Inelastic scattering in BPI must therefore also be important.

Khazanov, George V.↗

NASA NTRS1992

Solar wind-magnetosphere interaction as simulated by a 3-D EM particle code

We present here our first results of simulating the solar wind-magnetosphere interaction with a new three-dimensional electromagnetic particle code. Hitherto such global simulations were done with MHD codes while lower-dimensional particle or hybrid codes served to account for microscopic processes and such transport parameters as have to be introduced ad hoc in MHD. Our kinetic model attempts to combine the macroscopic and microscopic tasks. It relies only on the Maxwell curl equation and the Lorentz equation for particles, which are ideally suited for computers. The preliminary results shown here are for an unmagnetized solar wind plasma streaming past a dipolar magnetic field. The results show the formation of a bow shock and a magnetotail, the penetration of energetic particles into cusp and radiation belt regions, and dawn-dusk asymmetries.

Buneman, Oscar↗

NASA NTRS1992

Recent results from studies of electron beam phenomena in space plasmas

The paper examines selected results from experiments, performed in 1980s, involving the ejection of beams of electrons from spacecraft. Special attention is given to the basic processes associated with the spacecraft charging, passive current collection, beam-atmosphere interactions, beam-plasma interactions, and neutral gas emission. Consideration is also given to future experiments on active electron beam ejections in space.

Neubert, Torsten↗

NASA NTRS1992

Studies of dynamic processes related to active experiments in space plasmas

This is the final report for grant NAGw-2055, 'Studies of Dynamic Processes Related to Active Experiments in Space Plasmas', covering research performed at the University of Michigan. The grant was awarded to study: (1) theoretical and data analysis of data from the CHARGE-2 rocket experiment (1keV; 1-46 mA electron beam ejections) and the Spacelab-2 shuttle experiment (1keV; 100 mA); (2) studies of the interaction of an electron beam, emitted from an ionospheric platform, with the ambient neutral atmosphere and plasma by means of a newly developed computer simulation model, relating model predictions with CHARGE-2 observations of return currents observed during electron beam emissions; and (3) development of a self-consistent model for the charge distribution on a moving conducting tether in a magnetized plasma and for the potential structure in the plasma surrounding the tether. Our main results include: (1) the computer code developed for the interaction of electrons beams with the neutral atmosphere and plasma is able to model observed return fluxes to the CHARGE-2 sounding rocket payload; and (2) a 3-D electromagnetic and relativistic particle simulation code was developed.

Banks, Peter M.↗

NASA NTRS1990

Plasma density enhancements created by the ionization of the Earth's upper atmosphere by artificial electron beams

Analytical calculations and experimental observations relating to the interaction with the Earth's upper atmosphere of electron beams emitted from low altitude spacecraft are presented. The problem is described by two coupled nonlinear differential equations in the up-going (along a magnetic field line) and down-going differential energy flux. The equations are solved numerically, using the MSIS atmospheric model and the IRI ionospheric model. The results form the model compare well with recent observations from the CHARGE 2 sounding rocket experiment. Two aspects of the beam-neutral atmosphere interaction are discussed. First, the limits on the electron beam current that can be emitted from a spacecraft without substantial spacecraft charging are investigated. This is important because the charging of the spacecraft to positive potentials limits the current and the escape energy of the beam electrons and thereby limits the ionization of the neutral atmosphere. As an example, we find from CHARGE 2 observations and from the model calculations that below about 180 km, secondary electrons generated through the ionization of the neutral atmosphere by 1 to 10 keV electron beams from sounding rockets, completely balance the beam current, thereby allowing the emission of very high beam currents. Second, the amount of plasma production in the beam-streak is discussed. Results are shown for selected values of the beam energy, spacecraft velocity, and spacecraft altitude.

Neubert, Torsten↗

NASA NTRS1990

Electron collection enhancement arising from neutral gas jets on a charged vehicle in the ionosphere

Observations of current collection enhancements due to cold nitrogen gas control jet emissions from a highly charged, isolated rocket payload in the ionosphere have been made during the cooperative high altitude rocket gun experiment (CHARGE) 2 using an electrically tethered mother/daughter payload system. The current collection enhancement was observed on a platform (daughter payload) located 100 to 400 m away from the main payload firing an energetic electron beam (mother payload). These results are interpreted in terms of an electrical discharge forming in close proximity to the daughter vehicle during the short periods of gas emission. The results indicate that it is possible to enhance the electron current collection capability of positively charged vehicles by means of deliberate neutral gas releases into an otherwise undisturbed space plasma. The results are also compared with recent laboratory observations of hollow cathode plasma contactors operating in the 'ignited' mode.

Gilchrist, Brian E.↗

NASA NTRS1989

A comparison of current-voltage relationships of collectors in the earth's ionosphere with and without electron beam emission

Currents measurements obtained by the two sections of the Cooperative High Altitude Rocket Gun Experiment-2 sounding rocket, a mother vehicle carrying a 1-keV electron gun and a daughter vehicle tethered to the mother, are compared with the results of previous models of current collection by a charged conductor in a plasma. The current collection of the daughter vehicle, a conducting body in the ionosphere, is found to agree with the Parker-Murphy (1967) limit. The additional current collection found for the mother vehicle is attributed to beam-plasma interactions.

Myers, Neil B.↗