Magnetosphere Seminars

Interpreting dust impact signals detected by antenna instruments

Speaker:Libor Nouzak (Charles University, Prague)
Date:Tuesday, Nov 28, 2017
Time:3:30 PM
Location:LASP Space Science Building, room N100 (1st floor)

Seminar Abstract:

Dust impact events have been registered by antenna instrument in space for decades, yet there is still no comprehensive understanding of the processes that couple transient dust impact plasmas to antennas to generate measurable signals. Here I will present the most recent results from an ongoing laboratory investigation of dust impacts on the scaled-down model of the Cassini spacecraft. The goal of the investigation is to clarify the microphysics how the RPWS (Radio Plasma Wave Science) instrument is registering dust impacts as a function of impact location, bias voltages and antenna configuration. RPWS consists of three and antennas with two of them usually configured as a dipole and the third operates in a monopole mode. The laboratory setup allows independent biasing of the spacecraft and each antenna. Small tungsten plates are used as impact location to provide high impact charge yields. The setup is bombarded with submicron-sized iron grains from a velocity range of 5–25 km/s using the 3 MV dust accelerator operated at the LASP facility of University of Colorado. The experimental results support the recent suggestion that antennas in a dipole mode are only sensitive to direct antenna impacts and remain insensitive to impacts on the spacecraft body. The latter can be registered only by the monopole. Charge recollection from the impact plasma by the spacecraft and/or the antennas and induced (or image) are identified as the processes responsible for generating antenna signals generation. The polarity and the amplitude of the detected signals depend on both on the impact location and the bias voltages applied.