Presentation #207.03 in the session Surface Processes on Mercury: ’Tis but a Scratch.
Introduction: The observed Na in Mercury’s exosphere [1,2] is a potential constraint for the surface composition of Mercury. A number of models have been developed to explain the Na exosphere [3,4] but the contribution from solar wind ion irradiation is poorly understood due to the lack of experimental data for regolith-like loose powders. To address this issue, we have built a novel apparatus to measure the doubly differential angular sputtering yields for various impactors and target materials. Here, we present our proof-of-principle measurements.
Experiment: 20-keV Kr+ ions impacted a polycrystalline copper slab at a polar angle of θ=45° and an azimuthal angle of φ=0°. The beam intensity and profile were monitored during irradiation. The total dose was 6.28E17 ions. Ejected particles were collected by catcher foils mounted on a half dome partially covering the sample. The catcher foils were gold-coated quartz crystals. The doubly differential sputtering yield at each foil position was determined from the mass gain of the foil divided by the total ion dose.
Simulations: We performed SDTrimSP  and molecular dynamics (MD) simulations  for comparison to the experiment. SDTrimSP uses the binary collision approximation and thus assumes sputtering to be a result of collisions involving atomic nuclei within the target. MD uses an interatomic potential to consider all atomic interactions in the system. For both cases we tracked the doubly differential angular distribution of ejected particles mapped to the positions of the foils.
Results and Discussions: Here we will present our initial experimental results, and discuss their implications for the SDTrimSP simulation tool that is commonly used by planetary scientists for modeling ion sputtering. We will also discuss planned future measurements.
Acknowledgments: We acknowledge support, in part, from NASA SSW and NIH.
References:  A. E. Potter et al. (1999) Space Sci. 47, 1441–1448.  R. J. Vervack et al. (2010) Science 329, 672–675.  R. M. Killen et al. (2018), in The View after MESSENGER, 407–429.  R. M. Killen et al. (2022) Planet. Sci. J. 3:139.  A. Mutzke et al. (2019), SDTrimSP Version 6.00.  L. S. Morrissey et al. (2021) J. Appl. Phys.130, 013302.