CORRELATIONS BETWEEN THE VEGA-2 PLASMA-WAVE (APV-N) AND DUST (SP-1) OBSERVATIONS AT COMET HALLEY

The low-frequency (0.03-25 Hz), low-sensitivity electric field waveforms recorded in the outer coma and simultaneous observations of the dust particle mass spectra have been used to investigate what were the effective areas for generation of impulses in various amplitude ranges by impacts of particles from particular mass channels. We applied the least squares method to solve the sets of linear equations relating the numbers of dust particles from different mass magnitudes and the numbers of APV-N impulses counted in the same time intervals. It has turned out that the areas for production of, e.g., positive impulses by particles from the mass magnitudes: 10-17-10-16, 10-16-10-15, 10-15-10-14 g, were equal to about 2.5, 6.3, and 4.0, respectively, in units of the SP-1 sensor are (81 cm2). We propose a mechanism which explains that the sensitivity of APV-N to dust impacts was roughly proportional to the particle mass if m<10-15 g and that the effective area for particles 10-15-10-14 g should be strongly reduced. Impulse generation by particles bigger than 10-14 g is also discussed. A relatively good correspondence between the experimental results and interpretation can be achieved if the impact ionization yield is assumed rather high and the expansion velocity of dust-induced plasma a few times less than quoted in the literature. © 1990.