Abstract DGP2026-57

As it has been very well explored in the literature, we know that dust grains will get charged by solar radiation and plasma particles interacting with them (emission electrons, ions, photoemission from solar flux and secondary electron), creating a corresponding current. Previous studies on the physics of dust grains in plasma found that there is a small grain (nanometer-sized) enhancement effect when it comes to the secondary electron emission. Secondary electron emission is the phenomenon where electrons are emitted/ejected from the dust grain after gaining enough kinetic energy from bombardment or radiation from incoming particles (mostly electrons). A factor of 2 to enhance the secondary electron emission was used in the literature, which may be a too simplistic way to characterize that process. The “real” augmentation effect probably cannot be fixed by a constant and depends on a complex interaction between different parameters such as the path of the incoming electrons, the material properties, penetration depth and grain size among them. The objective of this research project was to familiarize myself with the charging process on a dust grain in a plasma environment, understand the small grain effect on the secondary electron emission yield and with that knowledge, then modify the existing charging code in a way that incorporates a more rigorous approach to quantifying the SEE (secondary electron emission). That new charging approach, I  have then applied to  a concrete example, here Saturn’s magnetosphere and rings, to see the potential effects it could have on the surface potential of a dust grain, depending on it's size. 
The results from the project showed that the modifications to an original charging code on a dust grain bring a significant enhancement of secondary electron emission for nanometric dust grain only. For each primary electron hitting the grain, a larger number of electrons is emitted, charging the grain more positively and settling the surface potential at a higher value. This was demonstrated within the context of nanometer sized dust grain from a distance of 3 to 20 L-shells in the Saturn's ring system. The results do suggest that the 2x factor used in the literature to take into account the small size grain effect is not accurate across all ranges of radii. Furthermore, the enhancement is also determined by a delicate balance of physical properties of the materials. Naturally, the effects that this underestimate can have in contexts such as nanometer sized particles in ring rain  or stream particles being ejected from the ring system should be investigated.