Abstract.Measurements

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Abstract-Analytical expressions for current to a cylindrical Langmuir probe at rest in unmagnetized plasma are compared with results from both steady-state Vlasov and particle-in-cell simulations. Probe bias potentials that are much greater than plasma temperature (assumed equal for ions and electrons), as of interest for bare conductive tethers, are considered. At a very high bias, both the electric potential and the attracted-species density exhibit complex radial profiles; in particular, the density exhibits a minimum well within the plasma sheath and a maximum closer to the probe. Excellent agreement is found between analytical and numerical results for values of the probe radius R close to the maximum radius -R max for orbital-motion-limited (OML) collection at a particular bias in the following number of profile features: the values and positions of density minimum and maximum, position of sheath boundary, and value of a radius characterizing the no-space-charge behavior of a potential near the high-bias probe. Good agreement between the theory and simulations is also found for parametric laws jointly covering the following three characteristic R ranges: sheath radius versus probe radius and bias for R <^i -Rmax! density minimum versus probe bias for R = _R max ; and (weakly bias-dependent) current drop below the OML value versus the probe radius for R > _R max .

Linear accelerators (linacs), capable of producing 5 MeV energy electron beams at 80 mA currents, are now down to a size that allow them to be flown on sounding rockets or balloons. This opens up new opportunities for atmospheric/ionospheric modification experiments where the mesosphere and thermosphere regions of the atmosphere can be perturbed down to 40 km altitude. In this paper beam propagation and atmospheric perturbation effects are studied by Monte Carlo simulations and by analytical means. It is shown that the earth' magnetic field severely limits the radial expansion of the beam otherwise induced by electron‐neutral collisions. It is also shown that the so‐called “envelope‐equations” from high‐energy laboratory physics adequately describe beam propagation in the upper atmosphere. The plasma density and electric conductivity modifications to the atmosphere are calculated from the Monte Carlo simulations. Inside the beam the conductivity in the 40–50 km altitude region is enhanced more than one order of magnitude by a 10 µs‐duration pulse. Some ideas for future scientific investigations are discussed, including the generation of electrical discharges by beams injected over thunderstorm regions.

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). We interpret these results 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. Our results are also compared with recent laboratory observations of hollow cathode plasma contactors operating in the “ignited” mode.