Magnetic Field Effect on Antenna Signals Induced by Dust Particle Impacts

The Radio and Plasma Wave Science instrument on Cassini has observed fewer than expected dust particle impacts during the mission's Grand Finale orbits. The relatively strong magnetic field in the close vicinity of the planet has been suggested to affect the intensity of the dust impact generated signals. A laboratory investigation is performed using dust particles accelerated to ≥20 km/s speed impacting onto a previously developed model of the spacecraft and the Radio and Plasma Wave Science antennas. The external magnetic field is generated by two sets of magnetic coils. The recorded antenna waveforms are decomposed into contributions from the electrons and ions of the dust impact generated plasma cloud. A good qualitative understanding of the waveforms is achieved by dividing the electron and ion population into two portions: one that is escaping from the spacecraft and another that is collected by the spacecraft. The experimental results show that the part of the signal corresponding to escaping electrons is affected by the magnetic field and that dust impact signals can be significantly reduced for spacecraft floating potentials close to zero.