Library

Notes: [Auszug] Each dust particle that hits the solid target of the SP-1 detector gives rise to a charged plasma cloud5; the amplitude of each charge pulse is measured and recorded by decade counters. A preliminary estimate for the mass range Amn of the nth channel is obtained by using an empirical conversion ...

Notes: [Auszug] The heart of the PUMA instrument is a time-of-flight mass spectrometer as described, for example, in ref. 2. When a dust particle strikes the target in front of the spectrometer, ions are formed, and those with positive charge are mass-analysed. Onboard electronics and microprocessor-control allow ...

Notes: Abstract The Giotto spacecraft is scheduled to intercept comet P/Grigg-Skjellerup on July 10, 1992. The observed outgassing rate of this comet is over an order of magnitude smaller than comet Giacobini-Zinner and over two orders of magnitude smaller than that of comet Halley. Consequently, the new data obtained during the upcoming encounter will strengthen our understanding of how the solar wind interaction with comets depends upon the neutral gas production rate. In this brief note, we make predictions of the location of the flow transition regions — i.e., the bow shock and the ionopause, and discuss the expected level of wave turbulence.

Notes: Abstract The disturbance of longitudinal waves by the interaction of a modulated flow of electrons with plasma is investigated. Conditions are found for the generation of instabilities, and the frequency spectrum and increment of growth of the oscillations are calculated.

Notes: Summary VLF quarter-gyrofrequency emissions, whose experimental characteristics differ from those of discrete plasmaspheric emissions usual during active times, have been observed by low-altitude Intercosmos 24 and Magion 2 satellites within the plasmasphere during periods of quieting geomagnetic activity. A new kind of instability is proposed which could lead to the production of these emissions. It is shown that quasi-electrostatic whistler waves can be generated in the eqquatorial region due to the fan instability, with maximum growth rate and spectral energy density in a frequency band below one half of the equatorial electron gyrofrequency. The observations of low-energy electrons and plasma waves in the equatorial region within or in the vicinity of the plasmapause, which could support our hypothesis experimentally, are discussed.

Notes: Abstract A solution is obtained for the problem of the propagation of electromagnetic waves of arbitrary form through a plasma boundary on condition that the length of the wave train is much greater than the wave length. A solution is found both for the case of a wide spectrum of width Δω much greater than the plasma frequency ω0, as well as for a narrow spectrum. The results obtained enable us to draw conclusions about the time and space variation of the shape of electromagnetic pulses in a plasma. The passage of high frequency electromagnetic waves through a plasma is similar to that of a beam of charged particles [1, 2]. This is associated with the fact that decay processes are similar to Cerenkov radiation effects. The dynamics of the development of transverse wave instabilities in a uniform Isotropic plasma were studied in [2] assuming that the wave phase behaves stochastically. It was calculated here that instabilities develop quite differently in the case of a wide frequency spectrum than in the case of a narrow “monochromatic” spectrum. If we can speak of transverse quanta diffusion effects in the “field” of the generated longitudinal quanta in the first case, and if the resulting effects are closely similar to the nonlinear effects arising when beam instability develops [3, 4], then the development of instabilities in the case of a narrow spectrum leads to the appearance of red satellites in the transverse wave spectrum differing from the basic frequencyω by a quantity νω0 (ν=1, 2, 3,...). In this case the development of the instability corresponds to a tendency for a plateau over the satellites to appear. Attention should however be drawn to the fact that the dynamics of instability development in a semibounded plasma may be quite different. This is associated first with the different values of group velocities of transverse and longitudinal waves, and what is also important, with the effect of longitudinal wave accumulation in the boundary region if the length of the wave train is sufficiently large. The treatment of a similar problem for beam instabilities in paper [5] showed that a narrow transition layer may arise with a transverse wave energy density greatly in excess of the energy density of the injected beam. In what follows we examine the part played by boundary effects in the passage of pulses of electromagnetic waves through the boundary of the plasma. The cases of both narrow and wide spectra are considered. We note that in the case of narrow spectra the wave train must necessarily be greatly in excess of Δω−1, and the effects of the accumulation of oscillations will be appreciable. The phases of both transverse waves, and also generated longitudinal waves are assumed to be stochastic quantities. The boundary effects which have been treated may be applied both in the generation of longitudinal waves necessary for the effective acceleration of particles in a plasma as well as in the modulation and alteration of the initial transverse wave spectrum. It should also be stressed that these effects which have been considered could be applied for turbulent plasma diagnostics, as has already been pointed out in [2].