Abstract
Abstract. We investigate the generation of charge due to collision between projectiles with sizes below ∼1 µm and metal surfaces at speeds ∼0.1 to 10 km s−1. This corresponds to speeds above the elastic limit and well below speeds where volume ionization can occur. Impact charge production at these low to intermediate speeds has traditionally been described by invoking the theory of shock wave ionization. By looking at the thermodynamics of the low-velocity solution of shock wave ionization, we find that such a mechanism alone is not sufficient to account for the recorded charge production in a number of scenarios in the laboratory and in space. We propose a model of capacitive contact charging that involves no direct ionization, in which we allow for projectile fragmentation upon impact. Furthermore, we show that this model describes measurements of metal–metal impacts in the laboratory well. We also address contact charging in the context of ice-on-metal collisions and apply our results to rocket observations of mesospheric dust. In general, we find that contact charging dominates at speeds of up to a few kilometres per second and complements shock wave ionization up to speeds where direct ionization can take place. The conditions that we consider can be applied 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.
Highlights
The variables in any experiment studying the impact of dust grains – be it of terrestrial, meteoric, interplanetary, or interstellar origin – span many orders of magnitude
For calculations of ice-on-metal charge yields, we assume that the ice particles are contaminated with meteoric smoke particles
In this work we have investigated the production of charge in impacts of projectiles of iron and agglomerates of ice and meteoric smoke on a metal surface at speeds 10 km s−1
Summary
The variables in any experiment studying the impact of dust grains – be it of terrestrial, meteoric, interplanetary, or interstellar origin – span many orders of magnitude. By variables we mean the aggregation of ambient parameters and intrinsic parameters of the projectile dust grains and impact surfaces The ambient parameters such as neutral and charged species densities and temperature can span several orders of magnitude. The mode of operation of such detectors is to measure the material-specific charge generation, which in general yields a semi-empirical relation of the form Q ∝ mαvβ. This allowed for detection of grains down to sizes ∼ 100 nm at speeds between the order of 1 km s−1 and some tens of km s−1.
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