A Comparison of Contact Charging and Impact Ionization in Low Velocity Impacts: Implications for Dust Detection in Space

Abstract

Abstract. We investigate the generation of charge during collision of projectiles with sizes below ~ 1 μm and metal surfaces at speeds ~ 0.1 km/s. This corresponds to speeds above the elastic limit and well below speeds where volume ionization can occur. The conditions that we consider apply to dust particles naturally occurring in space and in Earth's upper atmosphere and their direct impacts on rockets, spacecraft, and impacts of secondary ejecta. We introduce a model of capacitive contact charging in which we allow for projectile fragmentation upon impact, and show that this model describes measurements of metal-metal impacts in the laboratory and in-situ measurements of dust in the Earth's atmosphere well. We have considered the utilization of our model for different scenarios in interplanetary space and in Earth's atmosphere. From this discussion we find it likely that our work can be employed in a number of situations where impact velocities are relatively small. Furthermore, we have discussed the thermodynamics of the low velocity solution of shock wave ionization, and conclude that the impurity charging effect utilized in the much used model of Drapatz and Michel (1974) does not sufficiently describe charge generation at impact speeds below a few kilometers per second. Consequently, impact charging at low speeds cannot be described with a Saha-solution.

Investigating the Dust Flux in the Meteoric Smoke Sampler (MESS) Instrument for Sampling Dust in the Mesosphere

“…Based on this we assume that for the ice particle collisions, one large fragment, with half the mass of the primary particle survives. The rest of the particle will be fragmented, following a fragmentation distribution based on the work by Antonsen et al (2020), which states that the fragments will follow an r −3 distribution, where r is the radius. We assume that the ice component of the fragments evaporates, and only the pure MSP are left.…”